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>> DAVID Malan: Kull dritt, merħba lura.

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Dan huwa CS50.

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Dan huwa l-bidu ta 'seba' ġimgħa.

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Allura huwa kien filwaqt li, hekk ħsibt aħna'd
tieħu tour whirlwind ta 'fejn aħna

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jitħalla 'off u fejn aħna qed tmur issa.

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>> Allura dan il-ħaġa hawn jista 'jkollhom
ikkawża xi Angst fl-ewwel.

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Iżda nisperaw, int jibdew
aklimatizza għal dak li din tindika hawn -

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star jirrappreżentaw pointer, li hija
biss dak, f'termini iktar laymans?

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Hekk huwa l-indirizz.

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>> Allura huwa l-indirizz ta '
xi ħaġa fil-memorja.

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U bdejna biex Qaxxar is-saffi
ftit ġimgħat ilu, l-affarijiet simili

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GetString u oħrajn funzjonijiet
dan il-ħin ikunu ġew jirritornaw

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indirizzi ta 'affarijiet fil-memorja, bħall-
indirizz ta 'l-ewwel karattru

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xi sekwenza.

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>> Allura aħna introdotti wkoll valgrind, li
inti ser tibda tuża għal din il-problema

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stabbiliti, b'mod partikolari għall-jmiss
problema stabbiliti kif ukoll.

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U valgrind ma dak għalina?

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Huwa jagħmel verifiki għat-tnixxija memorja, u
wkoll kontrolli għall-abbuż ta 'memorja.

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>> Hija tista ', b'xi probabbilità, l-iskoperta jekk
kodiċi tiegħek se tmiss memorja

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li hija sempliċement mhux suppost.

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Allura mhux neċessarjament tnixxija, imma jekk inti
jmorru lil hinn mill-konfini ta 'xi

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array, u inti tmexxi effettivament valgrind
u jinduċi li l-imġieba waqt

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valgrind tkun qed taħdem fil-programm tiegħek huwa
tmexxija ġewwa ta 'dan, int ser tingħata

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messaġġi bħal dan - "invalidi ikteb tal
daqs 4, "li, tfakkar koppja ta '

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ġimgħat ilu kien ifisser li kelli aċċidentalment
bħal fuq int wieħed wisq

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lil hinn mill-konfini ta 'firxa.

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U hekk daqs 4 ifisser hawn id-daqs
ta 'dak int partikolari.

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>> Sabiex jieħdu riassigurazzjoni fil-fatt li
output valgrind, il-format ta 'dan,

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huwa biss atroċi.

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Huwa verament diffiċli li tara permezz tal-mess
għall-informazzjoni interessanti.

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Allura dak li aħna ghamilt hawn huwa biss silta
xi wħud mill-koppja ta 'aktar

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linji interessanti.

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Imma tirrealizza li 80% tal-tal valgrind
output se tkun daqsxejn ta '

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distrazzjoni.

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>> Just tfittex għal xejriet bħal dawn -
invalidu dritt, invalidu jinqraw, 40 bytes

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u xi numru ta 'blokki huma definittivament
mitlufa, keywords bħal dik.

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U dak li inti ser nisperaw tara xi
tip ta 'traċċa ta' liema funzjoni tal-

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żball huwa attwalment pulzieri

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F'dan il-każ hawnhekk, b'liema linja ta '
kodiċi tiegħi kien l-iżball apparentement?

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>> 26 fil-fajl imsejjaħ memory.c, li kienet
l-eżempju aħna kienu jilagħbu ma

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fil-ħin.

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Allura huwa probabbilment mhux fil malloc.

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Kien probabbilment fil-kodiċi tiegħi minflok.

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Allura aħna ser tara dan mill-ġdid
u għal darb'oħra qabel twil.

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>> Allura scanf, dan ħareġ fil-
Koppja ta 'forom s'issa.

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Rajna sscanf qosor.

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Din kienet xi ħaġa numru ta '
inti dived fis fis tiegħek

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tħejjijiet għall-kwizz.

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U scanf huwa attwalment dak li l-CS50
librerija kien jużaw taħtha l-

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hood għal żmien pjuttost twil sabiex
biex tikseb input mill-utent.

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>> Per eżempju, jekk I jimxu lejn CS50
appliance hawn, let me tiftaħ

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eżempju illum li sejjaħ scanf-0.c
U huwa sempliċi super.

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Huwa biss ftit linji ta 'kodiċi.

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Iżda huwa verament juri kif getInt
ilha taħdem kollha ta 'dan iż-żmien.

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>> F'dan il-programm hawn, f'konformità 16
, Avviż li jien tiddikjara int.

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Sabiex l-ebda pointers, xejn maġika
hemm, biss int.

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Imbagħad fil-linja 17, I-pront il-
utent għal numru, jekk jogħġbok.

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Imbagħad fl-aħħar 18, I-użu scanf hawn.

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And I speċifikat, tip simili printf,
li jien jistennew quote

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unquote mija i.

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>> Allura fil-mija i, naturalment,
tindika l-int.

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Imma avviż dak it-tieni
argument li scanf huwa.

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Kif tiddeskrivi t-tieni
argument wara l-virgola?

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X'inhu dan?

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>> Hu l-indirizz ta 'x.

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Allura dan huwa utli għaliex billi tipprovdi
scanf bl-indirizz ta 'x, dak ma

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li jagħtu s-setgħa dik il-funzjoni li tagħmel?

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Mhux biss jmorru hemm, iżda wkoll jagħmel xiex?

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>> Agħmel bdil għalih.

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Għaliex inti tista 'tmur hemm, huwa tip ta'
bħal mappa għal post fil-memorja.

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U sakemm inti tipprovdi scanf, jew
xi funzjoni mappa bħal din, dik

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funzjoni tista 'tmur hemm, u mhux biss
tħares lejn il-valur, iżda tista 'wkoll

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bidla li valur, li huwa utli jekk
l-iskop fil-ħajja ta 'scanf huwa li

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skennjati input mill-utent, speċifikament
mill-keyboard.

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U l-f tindika ifformattjat, bħad
printf, il-f jiddenota ifformattjat

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string li inti tixtieq li jistampaw.

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>> Għalhekk fil-qosor, din il-linja 18 sempliċiment jgħid,
jippruvaw jaqra int mill-utent tal-

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keyboard u jaħżnu ġewwa ta 'x, fi
tkun xi tkun l-indirizz x jiġri li jgħixu.

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U mbagħad fl-aħħar, linja 19 biss jgħid,
grazzi għall-int, f'dan il-każ.

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>> So let me imorru quddiem u jagħmlu dan.

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Sabiex tagħmel scanf 0.

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Let me imorru quddiem u zoom pulzieri

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I ser tmur u run dan ma
tikek slash scanf 0.

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Numru, jekk jogħġbok?

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50.

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Grazzi għall-50.

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Allura huwa pjuttost sempliċi.

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>> Issa dak li ma tagħmel?

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Huwa ma tagħmel mazz sħiħ
ta 'verifika żball.

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Per eżempju, jekk jien ma tikkoperax,
u jien ma tip fil-numru, iżda

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minflok I jiktbu xi ħaġa bħal "hello,"
li jinsab biss it-tip ta 'stramba.

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U għalhekk waħda mill-affarijiet l-CS50
librerija kienet tagħmel għalina għal xi

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ħin huwa li reprompting
u reprompting.

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>> Il retry frażi irtirar kien cs50.c,
u dak l-raġuni li getInt fl

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il-librerija CS50 huwa attwalment sħiħa
mazz ta 'konzijiet, għaliex aħna qed

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verifika għall-għalf stupid bħal dan.

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Did-utent ma jagħtux
us, fil-fatt, int?

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Did hu jew hi tagħtina xi ħaġa
Qisha ittra alfabetika?

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Jekk iva, irridu jikxfu
li u Yell fil minnhom.

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>> Imma l-affarijiet nikseb aktar interessanti
f'dan l-eżempju li jmiss.

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Jekk immur għall scanf-1.c, liema huwa l-waħda
ħaġa li hija fundamentalment mibdula

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dan l-eżempju li jmiss?

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Qed nuża char *, naturalment,
minflok int.

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>> Allura dan huwa interessanti, għaliex char *,
recall, huwa verament ftit l-

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istess ħaġa bħat string.

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Allura jħoss simili forsi dan huwa super
implimentazzjoni sempliċi ta 'GetString.

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Imma stajt imqaxxar lura s-saff
tal-librerija CS50, hekk jien

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ssejjaħ dan char * issa.

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Mela ejja ara fejn, jekk kullimkien,
immorru ħażin.

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>> Line 17 -

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I darb'oħra ngħid, jekk jogħġbok agħti me xi ħaġa,
f'dan il-każ, string.

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U mbagħad fil-linja li jmiss, I-sejħa scanf,
għal darb'oħra, jtuha kodiċi format,

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iżda din id-darba fil-mija s.

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U allura din id-darba, jien
tagħtiha buffer.

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>> Issa avviż, jien ma jużaw
l-ampersand.

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Iżda għaliex huwa li probabbilment OK hawn?

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Għaliex dak li hu buffer diġà?

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Huwa diġà pointer.

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Huwa diġà l-indirizz.

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>> U ejja din il-kelma "jikkonfondi," let me
biss sejħa hija s, per eżempju, għall-

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sempliċità.

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Imma stajt imsejħa buffer għaliex
ġenerali, fl-ipprogrammar, jekk għandek

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blokki ta 'memorja, li string verament
biss huwa, inti tista 'sejħa hija ta' buffer.

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Huwa post biex jaħżnu informazzjoni.

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>> Simili għal affarijiet bħal YouTube, meta
dawn qed lqugħ, biex ngħidu hekk, li

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ifisser biss huwa tniżżil bits minn
l-internet u jinħażnu f'dessikatur

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array lokali, blokki lokali ta 'memorja hekk
inti tista 'tara dan aktar tard mingħajr

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huwa taqbeż jew li jiddendlu fuq
inti waqt li jilagħbu lura.

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>> Allura hemm problema hawn għalkemm,
għaliex jien javżak scanf, jistennew

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string mill-utent.

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Hawn-indirizz ta '
blokki ta 'memorja.

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Poġġi li string hemmhekk.

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Għaliex huwa li marbuta tagħti
us inkwiet, għalkemm?

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>> X'hemm li?

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Am I permess għall-aċċess
dik il-parti tal-memorja?

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You know, I do not know.

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Minħabba jkun buffer ġew initialized
għal xejn?

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Mhux tassew.

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U dan huwa dak li konna qed jappellaw
valur żibel, li

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mhijiex kelma formali.

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00:06:44,040 --> 00:06:49,200
Dan ifisser biss aħna għandna ebda idea dak bits
huma ġewwa mill-erba 'bytes li

146
00:06:49,200 --> 00:06:51,240
Għandi allokati kif buffer.

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00:06:51,240 --> 00:06:52,450
>> I ma imsejħa malloc.

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00:06:52,450 --> 00:06:53,940
Stajt definittivament mhux imsejħa GetString.

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Allura li jaf dak li huwa effettivament
ġewwa ta 'buffer?

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And yet javżak scanf addoċċ, jmorru hemm
u tpoġġi ikun x'ikun l-utent ittajpjat.

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>> Allura dak li huwa probabbli li jikkawża
fil-kodiċi tagħna jekk aħna run?

152
00:07:04,460 --> 00:07:05,700
Probabbilment segfault.

153
00:07:05,700 --> 00:07:07,970
Forsi le, imma probabbilment segfault.

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00:07:07,970 --> 00:07:10,620
U jien ngħid forsi mhux għaliex kultant
inti tagħmel, xi kultant

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00:07:10,620 --> 00:07:11,380
inti ma tieħux segfault.

156
00:07:11,380 --> 00:07:14,280
Kultant inti biss tikseb xxurtjati, iżda
huwa madankollu se tkun

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bug fil-programm tagħna.

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>> So let me go quddiem u jiġbor dan.

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00:07:17,060 --> 00:07:18,280
Jien ser tagħmel dan il-mod qodma iskola.

160
00:07:18,280 --> 00:07:23,825
Allura sing clang 0, scanf-1,
scanf-1.C, Ikteb.

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Oops, skola wisq antik.

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Ejja ara.

163
00:07:26,550 --> 00:07:28,440
Fejn ma mmur?

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Oh, char * buffer.

165
00:07:29,700 --> 00:07:33,595

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Oh, grazie -

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Ħlief, OK -

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iskola antika ħafna.

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Kull dritt, huwa kien filwaqt li.

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>> So I stajt biss salvati l-fajl wara
jagħmlu dik temporanja

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bidla mument ilu.

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U issa I jikkompilaw dan
manwalment bl clang.

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U issa jien se jimxi 'l quddiem
u run scanf-1, Ikteb.

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String jekk jogħġbok.

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00:07:50,290 --> 00:07:51,600
I ser tip "bonjour."

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>> U issa, hawn fejn, franchement, printf
tista hija ftit annoying.

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Mhuwiex fil-fatt se
segfault f'dan il-każ.

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00:07:56,020 --> 00:07:59,860
Printf hija ftit speċjali minħabba
huwa tant super komunement użati li

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00:07:59,860 --> 00:08:03,570
essenzjalment printf qed tagħmel
us a favor u t-twettiq,

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li mhux pointer valida.

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Let me teħodha fuq ruħi biss print
out fil-parentesi null, anke

182
00:08:09,080 --> 00:08:13,340
għalkemm mhuwiex neċessarjament dak
aħna lilna nfusna mistennija.

183
00:08:13,340 --> 00:08:16,940
>> Allura ma nistgħux verament faċilment jinduċi
segfault ma 'dan, iżda b'mod ċar dan

184
00:08:16,940 --> 00:08:18,600
mhuwiex l-imġieba ridt.

185
00:08:18,600 --> 00:08:19,800
Allura x'inhu l-soluzzjoni sempliċi?

186
00:08:19,800 --> 00:08:25,650
Ukoll, fil-scanf-2, let me jipproponi li
minflok attwalment biss allokazzjoni ta '

187
00:08:25,650 --> 00:08:30,100
char *, let me jkun ftit aktar intelliġenti dwar
dan, u let me jallokaw buffer

188
00:08:30,100 --> 00:08:32,940
bħala sekwenza ta '16 Chars.

189
00:08:32,940 --> 00:08:34,200
>> So I tista 'tagħmel dan fi ftit ta' modi.

190
00:08:34,200 --> 00:08:35,610
I jistgħu assolutament użu malloc.

191
00:08:35,610 --> 00:08:38,980
Imma I tista 'tmur lura għal żewġ ġimgħa meta
I biss meħtieġ mazz sħiħ ta '

192
00:08:38,980 --> 00:08:39,620
karattri.

193
00:08:39,620 --> 00:08:40,860
Li jinsab biss firxa.

194
00:08:40,860 --> 00:08:44,870
So let me minflok tirridefinixxi buffer
li tkun firxa ta '16 karattri.

195
00:08:44,870 --> 00:08:47,340
>> U issa, meta I jgħaddu buffer fil -

196
00:08:47,340 --> 00:08:49,940
u din hija xi ħaġa aħna ma
jitkellmu dwar f'żewġ ġimgħa -

197
00:08:49,940 --> 00:08:53,730
imma int tista 'tittratta firxa kif
għalkemm huwa ta 'indirizz.

198
00:08:53,730 --> 00:08:56,390
Teknikament, kif aħna stajt tidher, dawn qed
ftit differenti.

199
00:08:56,390 --> 00:09:01,290
Iżda scanf mhux se mind jekk inti tgħaddiha
l-isem ta 'firxa, għaliex dak

200
00:09:01,290 --> 00:09:05,030
Clang se tagħmel għalina huwa essenzjalment
jikkura l-isem ta 'dak array bħala l-

201
00:09:05,030 --> 00:09:08,280
indirizz tal-blokki ta '16 bytes.

202
00:09:08,280 --> 00:09:09,550
>> Allura dan huwa aħjar.

203
00:09:09,550 --> 00:09:12,110
Dan ifisser li issa nista nisperaw
tagħmel dan li ġej.

204
00:09:12,110 --> 00:09:16,800
Let me zoom out għal mument u
ma jagħmlu scanf-2, miġbura OK.

205
00:09:16,800 --> 00:09:19,390
Issa let me do ltqajna slash scanf-2.

206
00:09:19,390 --> 00:09:22,430
String jekk jogħġbok. "Hello." U
deher li jaħdmu f'dan il-ħin.

207
00:09:22,430 --> 00:09:26,020
>> Iżda jista 'xi ħadd tipproponi xenarju
li fiha ma jkunx jista 'għadhom jaħdmu?

208
00:09:26,020 --> 00:09:28,550
Yeah?

209
00:09:28,550 --> 00:09:30,640
Xi ħaġa itwal minn 16 karattru.

210
00:09:30,640 --> 00:09:32,020
U fil-fatt, nistgħu nkunu
ftit aktar preċiża.

211
00:09:32,020 --> 00:09:36,540
Xi ħaġa itwal imbagħad 15 karattri,
għaliex verament għandna bżonn li wieħed iżomm f'moħħu

212
00:09:36,540 --> 00:09:39,920
li għandna bżonn li backslash żero
impliċitament fl-aħħar tas-sekwenza,

213
00:09:39,920 --> 00:09:42,950
li hija twarrib scanf se tipikament
jieħdu ħsieb ta għalina.

214
00:09:42,950 --> 00:09:46,210
>> So let me tagħmel xi ħaġa simili -

215
00:09:46,210 --> 00:09:48,040
kultant nistgħu biss
leave bħal dik.

216
00:09:48,040 --> 00:09:50,630
OK, hekk aħna issa stajt indotta
tort segmentazzjoni tagħna.

217
00:09:50,630 --> 00:09:51,000
Għaliex?

218
00:09:51,000 --> 00:09:54,940
Minħabba I ittajpjat għal aktar minn 15
karattri, u hekk aħna ħadthom attwalment

219
00:09:54,940 --> 00:09:58,280
memorja mimsus li I attwalment
m'għandux ikollhom.

220
00:09:58,280 --> 00:10:00,180
>> Allura x'hemm verament-soluzzjoni hawn?

221
00:10:00,180 --> 00:10:02,210
Ukoll, dak li jekk għandna bżonn string itwal?

222
00:10:02,210 --> 00:10:03,960
Well, aħna forsi jagħmilha 32 bytes.

223
00:10:03,960 --> 00:10:05,160
Ukoll, dak li jekk dan mhux twil biżżejjed?

224
00:10:05,160 --> 00:10:06,040
Kif madwar 64 bytes?

225
00:10:06,040 --> 00:10:07,080
X'jiġri jekk dan mhux twil biżżejjed?

226
00:10:07,080 --> 00:10:09,640
Kif madwar 128 jew 200 bytes?

227
00:10:09,640 --> 00:10:12,660
Dak li hu verament-soluzzjoni hawn fil-
każ ġenerali, jekk ma nafux fl

228
00:10:12,660 --> 00:10:14,460
tavvanza dak l-utent għaddej biex tip?

229
00:10:14,460 --> 00:10:20,000

230
00:10:20,000 --> 00:10:23,050
>> Huwa biss tip ta 'uġigħ kbir fl-ħmar,
li tkun onest, u huwa għalhekk li l-

231
00:10:23,050 --> 00:10:29,050
CS50 librerija għandha linji ftit għexieren ta '
kodiċi li jimplimentaw kollettivament

232
00:10:29,050 --> 00:10:32,390
GetString string b'mod li aħna ma
għandek tkun taf minn qabel liema l-

233
00:10:32,390 --> 00:10:33,430
utent se tip.

234
00:10:33,430 --> 00:10:37,370
B'mod partikolari, jekk inti tħares lura lejn
cs50.c minn ġimgħatejn ilu, tkun taf tara

235
00:10:37,370 --> 00:10:40,480
li GetString attwalment ma
jużawx scanf b'dan il-mod.

236
00:10:40,480 --> 00:10:43,720
Pjuttost, jgħid karattru wieħed
fi żmien.

237
00:10:43,720 --> 00:10:46,010
>> Minħabba li l-unika ħaġa sbieħ dwar
qari karattru wieħed huwa nistgħu

238
00:10:46,010 --> 00:10:48,490
jiggarantixxu nfusna li dejjem
jkollhom char inqas wieħed.

239
00:10:48,490 --> 00:10:51,740
I tista 'biss tiddikjara char, u mbagħad ħu
dawn il-passi verament tarbija biss

240
00:10:51,740 --> 00:10:54,380
taqra karattru wieħed fi fi
ħin mill-keyboard.

241
00:10:54,380 --> 00:10:58,240
U allura, dak li inti ser tara GetString
ma huwa kull darba li runs out ta ',

242
00:10:58,240 --> 00:11:02,280
jiġifieri, 16 bytes tal-memorja, hija tuża
malloc, jew ku tiegħu, li

243
00:11:02,280 --> 00:11:06,810
jallokaw aktar memorja, ikkupjar l-qodma
memorja fil-ġdida, u mbagħad crawling

244
00:11:06,810 --> 00:11:09,900
flimkien, jkollna karattru wieħed fi żmien,
u meta runs out ta 'dak

245
00:11:09,900 --> 00:11:13,370
blokki ta 'memorja, throws bogħod, grabs
blokki akbar ta 'memorja, kopji qodma

246
00:11:13,370 --> 00:11:14,750
fis ġodda, u jirrepeti.

247
00:11:14,750 --> 00:11:18,480
U huwa verament uġigħ li attwalment
timplimenta xi ħaġa sempliċi kemm

248
00:11:18,480 --> 00:11:19,710
jkollna input minn utent.

249
00:11:19,710 --> 00:11:21,090
>> Allura inti tista 'tuża scanf.

250
00:11:21,090 --> 00:11:22,430
Tista 'tuża funzjonijiet oħra simili.

251
00:11:22,430 --> 00:11:25,420
U ħafna ta 'kotba u online
eżempji jagħmlu, iżda dawn qed kollha

252
00:11:25,420 --> 00:11:27,210
vulnerabbli għal problemi bħal dan.

253
00:11:27,210 --> 00:11:29,550
U finalment, jkollna a segfault
huwa tip ta 'annoying.

254
00:11:29,550 --> 00:11:30,680
Mhuwiex tajjeb għall-utent.

255
00:11:30,680 --> 00:11:33,560
>> Iżda fl-agħar każ, dak ma
huwa fundamentalment tpoġġi tiegħek

256
00:11:33,560 --> 00:11:37,160
kodiċi f'riskju ta '?

257
00:11:37,160 --> 00:11:39,250
Xi tip ta 'attakk, potenzjalment.

258
00:11:39,250 --> 00:11:41,680
Tkellimna dwar wieħed attakk -
overflowing-munzell.

259
00:11:41,680 --> 00:11:44,660
Iżda b'mod ġenerali, jekk int permess biex
overflow buffer, bħal għamilna a

260
00:11:44,660 --> 00:11:48,070
Koppja ta 'ġimgħat ilu, biss bil-miktub
aktar minn "bonjour" fuq il-munzell, inti

261
00:11:48,070 --> 00:11:52,330
tista 'tabilħaqq tieħu f'idejha, ​​potenzjalment, a
kompjuter, jew għall-inqas tikseb lejn id-data li

262
00:11:52,330 --> 00:11:53,510
ma jappartjenix lilek.

263
00:11:53,510 --> 00:11:55,970
>> Għalhekk fil-qosor, dan huwa għaliex għandna
dawk ir-roti ta 'taħriġ.

264
00:11:55,970 --> 00:11:59,090
Imma issa, aħna jibdew teħodhom off,
bħala programmi tagħna m'għadx għandhom bżonn,

265
00:11:59,090 --> 00:12:00,610
neċessarjament, input mill-utent.

266
00:12:00,610 --> 00:12:03,960
Iżda fil-każ ta 'problema stabbiliti sitt,
input tiegħek se jiġu minn enormi

267
00:12:03,960 --> 00:12:07,520
fajl dizzjunarju b'150 xi
fard elf kelma.

268
00:12:07,520 --> 00:12:10,330
>> Allura inti mhux ser ikollhom għalfejn tinkwieta dwar
input arbitrarja l-utent.

269
00:12:10,330 --> 00:12:13,720
Aħna ser jagħtuk xi suppożizzjonijiet
dwar dan il-fajl.

270
00:12:13,720 --> 00:12:20,340
Kwalunkwe mistoqsijiet dwar pointers jew scanf
jew input utent b'mod ġenerali?

271
00:12:20,340 --> 00:12:24,450
>> Kull dritt, hekk ħarsa imbagħad lejn wieħed
batuta suġġett minn ġimgħatejn ilu.

272
00:12:24,450 --> 00:12:28,590
U li kien dan il-kunċett ta 'Struct.

273
00:12:28,590 --> 00:12:34,180
Mhux li - din l-idea ta '
Struct, li kien dak?

274
00:12:34,180 --> 00:12:35,430
What did Struct do għalina?

275
00:12:35,430 --> 00:12:39,280

276
00:12:39,280 --> 00:12:39,860
>> Iddefinixxi -

277
00:12:39,860 --> 00:12:41,710
sorry?

278
00:12:41,710 --> 00:12:42,820
Tiddefinixxi tip varjabbli.

279
00:12:42,820 --> 00:12:44,410
Allura sort ta '.

280
00:12:44,410 --> 00:12:46,180
Aħna fil-fatt tgħaqqad żewġ suġġetti.

281
00:12:46,180 --> 00:12:49,510
Allura ma typedef, ifakkar li nistgħu
tiddikjara tip ta 'tagħna stess, bħal

282
00:12:49,510 --> 00:12:51,500
sinonimu, bħal string għal char *.

283
00:12:51,500 --> 00:12:56,200
Iżda bl-użu typedef u Struct, nistgħu
joħolqu verament strutturi ta 'dejta tagħna stess.

284
00:12:56,200 --> 00:12:59,600
>> Per eżempju, jekk immur lura fis gedit
hawn għal ftit mument, u I jimxi 'l quddiem

285
00:12:59,600 --> 00:13:08,230
u tagħmel xi ħaġa simili, let me jiffrankaw
dan bħala, ejja ngħidu, structs.c

286
00:13:08,230 --> 00:13:10,840
temporanjament, jien biss ser
jimxi 'l quddiem u jinkludu

287
00:13:10,840 --> 00:13:14,360
standardio.h, null prinċipali int.

288
00:13:14,360 --> 00:13:18,960
U mbagħad fil hawn, ejja ngħidu li nixtieq
li jikteb programm li taħżen

289
00:13:18,960 --> 00:13:21,840
studenti multipli mill multipli
djar, per eżempju.

290
00:13:21,840 --> 00:13:24,430
Allura huwa simili registrarial
database ta 'xi tip.

291
00:13:24,430 --> 00:13:29,550
>> Hekk jekk I bżonn l-isem istudent waħda, I
tista 'tagħmel xi ħaġa bħall-isem * char,

292
00:13:29,550 --> 00:13:31,570
u jien ser tagħmel xi ħaġa simili -

293
00:13:31,570 --> 00:13:34,410
attwalment, ejja jużaw il-librerija CS50
għal ftit mument biex jagħmlu dan

294
00:13:34,410 --> 00:13:38,380
ftit aktar sempliċi, sabiex inkunu nistgħu tissellef
dawk għexieren ta 'linji ta' kodiċi.

295
00:13:38,380 --> 00:13:39,340
U ejja biss jżommha sempliċi.

296
00:13:39,340 --> 00:13:42,610
Aħna ser jżommha string,
u issa GetString.

297
00:13:42,610 --> 00:13:47,420
>> So I pretensjoni issa li stajt maħżuna l-isem
ta 'xi student, u l-dar ta'

298
00:13:47,420 --> 00:13:50,240
xi student, sempliċement jużaw fatturi varjabbli
bħal għamilna u fil-ġimgħa.

299
00:13:50,240 --> 00:13:52,370
Imma suppose I issa jridu jappoġġjaw
istudenti multipli.

300
00:13:52,370 --> 00:13:58,460
Kull dritt, hekk instincts tiegħi huma jagħmlu
string Isem2, gets GetString, spag

301
00:13:58,460 --> 00:14:01,370
house2 gets GetString.

302
00:14:01,370 --> 00:14:05,850
U allura tielet student tagħna,
ejja do name3 GetString.

303
00:14:05,850 --> 00:14:09,170
>> Kull dritt, għalhekk dan huwa wieħed jittama impressjonanti
inti bħala tip ta 'stupid,

304
00:14:09,170 --> 00:14:11,580
minħabba dan il-proċess huwa verament qatt
ser jispiċċaw, u huwa biss se

305
00:14:11,580 --> 00:14:13,130
jagħmlu kodiċi tiegħi ħarsa agħar
u agħar u agħar.

306
00:14:13,130 --> 00:14:14,810
Iżda aħna solvuta din wisq ġimgħatejn.

307
00:14:14,810 --> 00:14:19,450
Liema kienet soluzzjoni relattivament nadif tagħna
meta kellna varjabbli multipli tal-

308
00:14:19,450 --> 00:14:23,580
istess tip ta 'data li huma kollha relatati, iżda
aħna ma tridx dan mess atroċi

309
00:14:23,580 --> 00:14:26,870
ta 'varjabbli bl-istess mod jismu?

310
00:14:26,870 --> 00:14:30,060
Dak li ma nagħmlu minflok?

311
00:14:30,060 --> 00:14:31,260
>> So I think I smajt ftit postijiet.

312
00:14:31,260 --> 00:14:32,590
Kellna firxa.

313
00:14:32,590 --> 00:14:37,110
Jekk inti tixtieq każi multipli ta '
xi ħaġa, għaliex ma aħna nadif dan kollu

314
00:14:37,110 --> 00:14:39,540
up u biss jgħidu, agħti lili
array ismijiet imsejħa?

315
00:14:39,540 --> 00:14:41,640
>> U għal issa, ejja kodiċi 3 tal iebsa.

316
00:14:41,640 --> 00:14:44,450
U mbagħad tagħti me firxa ieħor
imsejħa djar, u let me għal

317
00:14:44,450 --> 00:14:45,800
Kodiċi issa hard 3.

318
00:14:45,800 --> 00:14:49,220
U stajt massiv mnaddfa l-
mess li I biss maħluqa.

319
00:14:49,220 --> 00:14:52,400
Issa, stajt għadu diffiċli kodifikati 3, iżda anke
3 tista dinamikament jiġu mill-

320
00:14:52,400 --> 00:14:54,350
utent, jew ARGV, jew simili.

321
00:14:54,350 --> 00:14:55,720
Allura dan huwa diġà aktar nodfa.

322
00:14:55,720 --> 00:15:00,100
>> Imma x'hemm annoying dwar dan hija li
issa, anki jekk l-isem huwa b'xi mod

323
00:15:00,100 --> 00:15:02,280
fundamentalment marbuta mal-
house ta 'student -

324
00:15:02,280 --> 00:15:04,720
huwa student li I really
rridu li jirrappreżentaw -

325
00:15:04,720 --> 00:15:08,080
I issa għandhom żewġ arrays li huma paralleli
fis-sens li dawn qed l-

326
00:15:08,080 --> 00:15:13,930
istess daqs, u l-ismijiet bracket 0
preżumibbilment mapep għall bracket djar 0,

327
00:15:13,930 --> 00:15:16,600
u ismijiet parentesi 1 mapep
għal djar bracket 1.

328
00:15:16,600 --> 00:15:19,280
Fi kliem ieħor, li student jgħix fil
dik id-dar, u li student ieħor

329
00:15:19,280 --> 00:15:20,530
jgħix fil dik id-dar oħra.

330
00:15:20,530 --> 00:15:23,720
Iżda żgur dan jista 'jkun
isir aktar nadif.

331
00:15:23,720 --> 00:15:24,990
>> Ukoll, tista ', fil-fatt.

332
00:15:24,990 --> 00:15:28,730
U let me imorru quddiem u tiftaħ
up structs.h, u tkun taf

333
00:15:28,730 --> 00:15:31,130
tara din l-idea hawnhekk.

334
00:15:31,130 --> 00:15:34,905
Avviż li stajt użati typedef, kif inti
allużjoni għall mument ilu li jiddikjara tagħna

335
00:15:34,905 --> 00:15:35,570
tip ta 'data stess.

336
00:15:35,570 --> 00:15:39,660
Imma jien wkoll jużaw dan il-keyword ieħor
imsejħa Struct li tagħti me a ġdid

337
00:15:39,660 --> 00:15:40,790
struttura tad-data.

338
00:15:40,790 --> 00:15:43,980
>> U din l-istruttura tad-data nitlob va
li jkollha żewġ affarijiet ġewwa ta '

339
00:15:43,980 --> 00:15:47,060
dan - string imsejjaħ isem, u
string imsejħa dar.

340
00:15:47,060 --> 00:15:49,820
U l-isem jien ser jagħti lill
din l-istruttura tad-data li qed jiġri

341
00:15:49,820 --> 00:15:51,005
li għandu jissejjaħ student.

342
00:15:51,005 --> 00:15:54,030
I jistgħu sejħa hija xejn nixtieq,
iżda dan jagħmlu semantikament

343
00:15:54,030 --> 00:15:55,810
sens li lili fil-fehma tiegħi.

344
00:15:55,810 --> 00:15:59,160
>> Allura issa, jekk I jiftħu verżjoni aħjar
tal-programm bdejt miktub

345
00:15:59,160 --> 00:16:00,390
hemm, let me iscroll għall-quċċata.

346
00:16:00,390 --> 00:16:03,190
U hemm ftit aktar linji ta 'kodiċi
hawn, iżda let me tiffoka għal

347
00:16:03,190 --> 00:16:04,160
il-mument fuq waħda.

348
00:16:04,160 --> 00:16:07,790
Stajt ddikjarat l-istudenti imsejħa kostanti
u diffiċli kodifikati 3 għal issa.

349
00:16:07,790 --> 00:16:11,110
Imma issa, avviż kif nadif
kodiċi tiegħi jibda biex tikseb.

350
00:16:11,110 --> 00:16:15,030
>> F'konformità 22, niddikjara
firxa ta 'studenti.

351
00:16:15,030 --> 00:16:18,760
U tinnota li student hija apparentement
issa 'tip data.

352
00:16:18,760 --> 00:16:23,360
Minħabba fil-quċċata ta 'dan il-fajl, avviż
Stajt inklużi dan il-fajl header

353
00:16:23,360 --> 00:16:24,820
li I jinġibed up ftit mument ilu.

354
00:16:24,820 --> 00:16:28,820
U dan il-fajl header sempliċement kellha
din id-definizzjoni ta 'student.

355
00:16:28,820 --> 00:16:32,470
>> Allura issa, stajt ħolqot data tad-dwana tiegħi stess
tip li l-awturi ta 'snin C

356
00:16:32,470 --> 00:16:33,890
ilu ma think ta 'qabel.

357
00:16:33,890 --> 00:16:34,570
Imma l-ebda problema.

358
00:16:34,570 --> 00:16:35,870
I jistgħu jagħmlu myself.

359
00:16:35,870 --> 00:16:39,050
Allura dan huwa firxa imsejħa istudenti,
kull membri li

360
00:16:39,050 --> 00:16:41,100
hija struttura student.

361
00:16:41,100 --> 00:16:44,270
U nixtieq tlieta minn dawk
fil-firxa.

362
00:16:44,270 --> 00:16:46,030
>> U issa, dak ma l-bqija
ta 'dan il-programm do?

363
00:16:46,030 --> 00:16:47,550
I meħtieġa xi ħaġa ftit arbitrarju.

364
00:16:47,550 --> 00:16:51,450
Allura minn online 24 onward,
I jtenni 0-3.

365
00:16:51,450 --> 00:16:54,000
I imbagħad titlob lill-utent għall-
isem l-istudent.

366
00:16:54,000 --> 00:16:56,110
U mbagħad I użu GetString bħal qabel.

367
00:16:56,110 --> 00:16:59,410
Imbagħad I jistaqsu għall-dar l-istudent,
u I-użu GetString bħal qabel.

368
00:16:59,410 --> 00:17:01,780
>> Iżda avviż - ftit ġdida
biċċa sintassi -

369
00:17:01,780 --> 00:17:07,010
I xorta tista indiċi għall-istudent i-th,
imma kif nista 'nikseb fuq l-informazzjoni speċifika

370
00:17:07,010 --> 00:17:08,354
ġewwa qasam tal-Struct?

371
00:17:08,354 --> 00:17:11,770
Well, x'hemm apparentement l-
biċċa ġdida ta 'sintassi?

372
00:17:11,770 --> 00:17:13,339
Huwa biss l-operatur dot.

373
00:17:13,339 --> 00:17:14,510
>> Imxejna ma verament rajt dan qabel.

374
00:17:14,510 --> 00:17:17,819
Inti stajt tidher fil pset ħames jekk inti stajt
dived diġà ma 'fajls Bitmap.

375
00:17:17,819 --> 00:17:22,372
Iżda l-dot ifisser biss ġewwa ta 'dan
Struct jew oqsma multipli, jagħtu dot

376
00:17:22,372 --> 00:17:24,510
isem, jew jagħtu me dot house.

377
00:17:24,510 --> 00:17:28,690
Dan ifisser mur ġewwa tal-Struct
u tikseb dawk l-oqsma partikolari.

378
00:17:28,690 --> 00:17:30,200
>> X'tagħmel l-bqija ta 'dan il-programm do?

379
00:17:30,200 --> 00:17:31,190
Huwa mhux kollha li sexy.

380
00:17:31,190 --> 00:17:34,640
Avviż li I jtenni 0-3 darb'oħra,
u I sempliċiment toħloq Ingliż

381
00:17:34,640 --> 00:17:40,500
frażi bħal hekk u hekk tkun tali u
tali dar, li jgħaddi fl-isem dot minn

382
00:17:40,500 --> 00:17:43,320
l-istudent i-th u tagħhom
dar kif ukoll.

383
00:17:43,320 --> 00:17:47,560
>> U mbagħad fl-aħħar, issa aħna ser tibda tikseb
anali dwar dan, issa li aħna qed

384
00:17:47,560 --> 00:17:49,580
familjari ma 'dak malloc u
funzjonijiet oħra ġew

385
00:17:49,580 --> 00:17:50,570
tagħmel dan il-ħin.

386
00:17:50,570 --> 00:17:54,220
Għaliex għandi ħielsa kemm isem
u d-dar, anki jekk I

387
00:17:54,220 --> 00:17:56,960
ma sejħa malloc?

388
00:17:56,960 --> 00:17:58,020
>> GetString għamlet.

389
00:17:58,020 --> 00:18:00,930
U li kien l-sigrieti ftit maħmuġa għal
diversi ġimgħat, iżda għandha GetString

390
00:18:00,930 --> 00:18:03,530
ġie jnixxu memorja kollha fuq il-
jpoġġi kull semestru s'issa.

391
00:18:03,530 --> 00:18:05,990
U valgrand se finalment
jiżvelaw dan lilna.

392
00:18:05,990 --> 00:18:10,730
>> Imma din mhix big deal, għaliex naf
li nista 'sempliċement ħielsa l-isem

393
00:18:10,730 --> 00:18:15,750
u l-dar, għalkemm teknikament, li
tkun super, sikur super, I għandu jkun

394
00:18:15,750 --> 00:18:17,890
tagħmel xi żball iċċekkjar hawn.

395
00:18:17,890 --> 00:18:19,040
Liema huma instincts tiegħek tghidlek?

396
00:18:19,040 --> 00:18:22,480
X'għandi nkun kontroll għall-
qabel I ħielsa x'inhi

397
00:18:22,480 --> 00:18:25,470
spag, aka li char *?

398
00:18:25,470 --> 00:18:33,460
>> I għandhom verament jiġi verifikat jekk l-istudenti
i bracket dot isem ma

399
00:18:33,460 --> 00:18:34,840
null ugwali.

400
00:18:34,840 --> 00:18:40,400
Imbagħad ser tkun OK biex jimxi 'l quddiem u ħielsa
li pointer, u bl-istess jew l-oħra

401
00:18:40,400 --> 00:18:41,160
waħda ukoll.

402
00:18:41,160 --> 00:18:46,860
Jekk istudenti bracket i dot house mhix
daqs null, dan issa se tipproteġi

403
00:18:46,860 --> 00:18:52,520
kontra l-każ kantuniera li fih
GetString prospetti xi ħaġa bħal null.

404
00:18:52,520 --> 00:18:57,310
U rajna mument ilu, printf se
tħarisna up here bi ftit qal

405
00:18:57,310 --> 00:18:58,990
null, li se tfittex stramb.

406
00:18:58,990 --> 00:19:02,340
Iżda mill-inqas mhux se segfault,
kif rajna.

407
00:19:02,340 --> 00:19:05,990
>> Well, let me jagħmlu ħaġa waħda oħra hawn.
structs-0 huwa tip ta 'programm stupid

408
00:19:05,990 --> 00:19:09,700
minħabba I jidħol dan kollu data, u mbagħad
huwa tilef ladarba l-programm jintemm.

409
00:19:09,700 --> 00:19:10,940
Iżda let me imorru quddiem u tagħmel dan.

410
00:19:10,940 --> 00:19:12,830
Let me jagħmlu l-terminal
tieqa daqsxejn akbar.

411
00:19:12,830 --> 00:19:17,000
Let me jagħmlu structs-1, li
huwa verżjoni ġdida ta 'dan.

412
00:19:17,000 --> 00:19:18,520
>> I ser zoom ftit.

413
00:19:18,520 --> 00:19:21,620
U issa let me run dot
slash structs-1.

414
00:19:21,620 --> 00:19:22,590
Isem istudent -

415
00:19:22,590 --> 00:19:31,500
David Mather, ejja tagħmel Rob Kirkland,
ejja do Lauren Leverett.

416
00:19:31,500 --> 00:19:33,650
X'hemm interessanti issa huwa avviż -

417
00:19:33,650 --> 00:19:35,540
u I biss jafu dan għaliex
I kiteb il-programm -

418
00:19:35,540 --> 00:19:38,930
hemm fajl issa 'kurrenti tiegħi
direttorju imsejjaħ students.csv.

419
00:19:38,930 --> 00:19:40,420
Xi wħud minnkom tista raw
dawn fid-dinja reali.

420
00:19:40,420 --> 00:19:42,980
>> X'hemm fajl CSV?

421
00:19:42,980 --> 00:19:44,170
Valuri separata bil-virgoli.

422
00:19:44,170 --> 00:19:46,670
Huwa tip ta 'prodotti simili raġel foqra
verżjoni ta 'fajl Excel.

423
00:19:46,670 --> 00:19:50,580
Huwa tabella ta 'ringieli u kolonni li
inti tista 'tiftaħ fi programm bħal Excel,

424
00:19:50,580 --> 00:19:51,800
jew numri fuq Mac.

425
00:19:51,800 --> 00:19:55,180
>> U jekk I miftuħa dan il-fajl hawn fuq gedit,
avviż - u n-numri ma jkunux hemm.

426
00:19:55,180 --> 00:19:57,360
Li jinsab biss gedit javżak
me linja numri.

427
00:19:57,360 --> 00:19:59,740
Avviż fuq l-ewwel linja ta 'dan
fajl huwa David u Mather.

428
00:19:59,740 --> 00:20:01,450
Il-linja li jmiss huwa Rob virgola Kirkland.

429
00:20:01,450 --> 00:20:04,170
U t-tielet linja hija Lauren
comma Leverett.

430
00:20:04,170 --> 00:20:05,480
>> Allura dak li I maħluqa?

431
00:20:05,480 --> 00:20:09,580
Stajt issa miktuba programm C li
effettivament jistgħu jiġġeneraw spreadsheets

432
00:20:09,580 --> 00:20:11,840
li jistgħu jinfetħu
programm bħal Excel.

433
00:20:11,840 --> 00:20:15,520
Mhux kollha li konvinċenti sett ta 'data, iżda
jekk għandek biċċiet ħafna akbar ta '

434
00:20:15,520 --> 00:20:18,440
data li inti fil-fatt tixtieq li
jimmanipulaw u jagħmlu graffs ta 'u l-

435
00:20:18,440 --> 00:20:21,260
simili, dan huwa forsi wieħed
mod biex jinħolqu dik id-data.

436
00:20:21,260 --> 00:20:25,370
Barra minn hekk, CSVs huma attwalment super komuni
biss għall-ħażna tad-data sempliċi -

437
00:20:25,370 --> 00:20:28,940
Yahoo Finanzi, per eżempju, jekk ikollok
stock kwotazzjonijiet permezz tal-hekk imsejħa tagħhom

438
00:20:28,940 --> 00:20:33,180
API, is-servizz b'xejn li ihallik
nikseb stock up-to-the-data attwali

439
00:20:33,180 --> 00:20:35,650
kwotazzjonijiet għall-kumpaniji, huma
jagħtu data lura fil-

440
00:20:35,650 --> 00:20:37,800
super format CSV sempliċi.

441
00:20:37,800 --> 00:20:39,380
>> Allura kif ma nagħmlu dan?

442
00:20:39,380 --> 00:20:42,530
Ukoll avviż, aktar ta 'dan tal-programm
kważi l-istess.

443
00:20:42,530 --> 00:20:46,870
Iżda avviż stabbiliti hawn, minflok print
l-istudenti li, mil-linja 35

444
00:20:46,870 --> 00:20:51,040
onward, I jsostnu li jien iffrankar l-
istudenti li disk, hekk iffrankar fajl.

445
00:20:51,040 --> 00:20:53,630
>> So avviż jien tiddikjara FILE * -

446
00:20:53,630 --> 00:20:57,260
issa, dan huwa tip ta 'anomalija fis C.
Għal kwalunkwe raġuni, FILE huwa caps kollha,

447
00:20:57,260 --> 00:21:00,690
li mhux simili ħafna tipi ta 'data oħra
fil C. Iżda din hija mibnija fil-

448
00:21:00,690 --> 00:21:02,320
tip ta 'data, FILE *.

449
00:21:02,320 --> 00:21:05,900
U jien tiddikjara pointer għall-fajl,
huwa kif inti tista 'taħseb li.

450
00:21:05,900 --> 00:21:08,070
>> fopen ifisser fajl miftuħ.

451
00:21:08,070 --> 00:21:09,470
What file tridu miftuħ?

452
00:21:09,470 --> 00:21:12,620
Irrid li tiftaħ fajl li jiena ser
arbitrarju sejħa students.csv.

453
00:21:12,620 --> 00:21:14,480
I tista 'sejħa li xejn irrid.

454
00:21:14,480 --> 00:21:15,200
>> U mbagħad tieħu raden.

455
00:21:15,200 --> 00:21:18,960
X'tagħmel l-tieni argument
li fopen probabilment tfisser?

456
00:21:18,960 --> 00:21:21,480
Dritt, w għall jiktbu, tista
jkun r għall read.

457
00:21:21,480 --> 00:21:24,120
Hemm għall tehmeż jekk inti
trid iżżid ringieli u mhux

458
00:21:24,120 --> 00:21:25,200
jissostitwixxu l-ħaġa sħiħa.

459
00:21:25,200 --> 00:21:28,005
>> Imma I biss jixtiequ joħolqu dan il-fajl
darba, so I ser tuża unquote w kwotazzjoni.

460
00:21:28,005 --> 00:21:31,880
U naf li biss meta tkun tinqara
id-dokumentazzjoni, jew il-paġna bniedem.

461
00:21:31,880 --> 00:21:35,100
Jekk fajl ma jkunx null - fi kliem ieħor,
jekk xejn marret ħażin hemmhekk -

462
00:21:35,100 --> 00:21:37,820
let me jtenni fuq il-
istudenti 0-3.

463
00:21:37,820 --> 00:21:40,410
>> U issa avviż li hemm xi ħaġa
dejjem hekk ftit differenti

464
00:21:40,410 --> 00:21:42,110
dwar il-linja 41 hawn.

465
00:21:42,110 --> 00:21:42,960
Mhuwiex printf.

466
00:21:42,960 --> 00:21:46,530
Huwa fprintf għal fajl printf.

467
00:21:46,530 --> 00:21:47,790
Allura li għaddej biex jikteb għall-fajl.

468
00:21:47,790 --> 00:21:48,860
Liema fajl?

469
00:21:48,860 --> 00:21:53,630
Il-wieħed li inti tispeċifika pointer
bħala l-ewwel argument.

470
00:21:53,630 --> 00:21:55,940
>> Imbagħad aħna tispeċifika string format.

471
00:21:55,940 --> 00:21:59,660
Imbagħad aħna tispeċifika liema string rridu
plug fl għall-ewwel i fil-mija, u

472
00:21:59,660 --> 00:22:04,320
imbagħad varjabbli ieħor jew
it-tieni fil-mija s.

473
00:22:04,320 --> 00:22:06,760
Imbagħad aħna qrib il-fajl ma fclose.

474
00:22:06,760 --> 00:22:09,380
Minn I tilliberalizza l-memorja bħal qabel, għalkemm
I għandhom imorru lura u żid

475
00:22:09,380 --> 00:22:10,540
xi kontrolli għal null.

476
00:22:10,540 --> 00:22:12,090
>> U li hu.

477
00:22:12,090 --> 00:22:16,960
fopen, fprintf, fclose me tagħti l-
kapaċità li joħolqu fajls test.

478
00:22:16,960 --> 00:22:19,640
Issa, tkun taf tara fil-problema sett ħames,
li tkun tinvolvi xbihat, inti ser tkun qed tuża

479
00:22:19,640 --> 00:22:20,990
fajls binarji minflok.

480
00:22:20,990 --> 00:22:24,200
Iżda fundamentalment, l-idea hija l-istess,
anki jekk il-funzjonijiet inti ser

481
00:22:24,200 --> 00:22:28,710
tara huma ftit differenti.

482
00:22:28,710 --> 00:22:32,580
>> Allura tour whirlwind, iżda inti se tikseb
wisq familjari mal-fajl I/O--

483
00:22:32,580 --> 00:22:34,960
input u output - ma pset ħamsa.

484
00:22:34,960 --> 00:22:38,607
U xi mistoqsijiet dwar l-
baŜi inizjali hawn?

485
00:22:38,607 --> 00:22:39,857
Yeah?

486
00:22:39,857 --> 00:22:41,880

487
00:22:41,880 --> 00:22:43,710
>> X'jiġri jekk inti tipprova teħles valur null?

488
00:22:43,710 --> 00:22:48,880
Nemmen, sakemm ħielsa gotten
ftit aktar faċli għall-utent, inti tista '

489
00:22:48,880 --> 00:22:49,890
potenzjalment segfault.

490
00:22:49,890 --> 00:22:54,160
Jgħaddiha null huwa ħażin minħabba I ma
jemmnu ħielsa bothers li jiċċekkja għalik,

491
00:22:54,160 --> 00:22:57,330
għaliex dan jista 'potenzjalement jkun skart
ta 'żmien biex tagħmel lilha nnifisha għal

492
00:22:57,330 --> 00:22:59,022
kulħadd fid-dinja.

493
00:22:59,022 --> 00:23:00,590
Mistoqsija tajba, għalkemm.

494
00:23:00,590 --> 00:23:04,300
>> Kull dritt, sabiex dan it-tip ta gets
ahna suġġett interessanti.

495
00:23:04,300 --> 00:23:07,010
It-tema tal-problema sett
ħamsa forensika.

496
00:23:07,010 --> 00:23:08,420
Mill-inqas dan huwa porzjon
tal-problema sett.

497
00:23:08,420 --> 00:23:12,030
Forensika ġeneralment jirreferi għall-
irkupru ta 'informazzjoni li jistgħu jew

498
00:23:12,030 --> 00:23:14,110
jista 'ma ġew imħassra
deliberatament.

499
00:23:14,110 --> 00:23:18,680
U hekk ħsibt I d jagħtik a quick
togħma ta 'dak li hu verament għaddejjin kollha

500
00:23:18,680 --> 00:23:21,230
din id-darba taħt il-
hood tal-kompjuter tiegħek.

501
00:23:21,230 --> 00:23:23,960
>> Per eżempju, jekk għandek ġewwa tal tiegħek
laptop jew kompjuter desktop tiegħek

502
00:23:23,960 --> 00:23:28,040
hard drive, huwa jew mekkaniku
apparat li attwalment spins -

503
00:23:28,040 --> 00:23:31,650
hemm affarijiet ċirkolari imsejħa platters
li tfittex pjuttost simili dak I

504
00:23:31,650 --> 00:23:34,540
biss kellhom up fuq l-iskrin hawn, għalkemm
dan huwa dejjem iskola antika.

505
00:23:34,540 --> 00:23:37,370
Dan huwa ta 'tliet u nofs pulzier
hard drive.

506
00:23:37,370 --> 00:23:40,070
U pulzieri tlieta u nofs jirreferi ta '
ma 'l-ħaġa meta inti jinstallaw dan

507
00:23:40,070 --> 00:23:40,890
fil-kompjuter.

508
00:23:40,890 --> 00:23:44,890
>> Ħafna minnkom guys fil laptops tiegħek issa
jkollhom drives stat solidu, jew SSDs,

509
00:23:44,890 --> 00:23:46,260
li ebda partijiet li jiċċaqalqu.

510
00:23:46,260 --> 00:23:49,170
Huma qed aktar bħal RAM u anqas simili
dawn il-mezzi mekkaniċi.

511
00:23:49,170 --> 00:23:51,450
Iżda l-ideat għadhom l-istess,
ċertament kif jirrelataw

512
00:23:51,450 --> 00:23:52,790
għall-problema stabbiliti ħamsa.

513
00:23:52,790 --> 00:23:57,400
>> U jekk taħseb dwar issa hard drive
jirrappreżenta tkun ċirku, li

514
00:23:57,400 --> 00:23:58,930
I ser tiġbed bħal dan hawn.

515
00:23:58,930 --> 00:24:02,290
Meta inti toħloq fajl fuq il-kompjuter tiegħek,
jekk huwa ta 'SSD, jew

516
00:24:02,290 --> 00:24:06,610
F'dan il-każ, l-anzjani iskola hard drive,
dan il-fajl jinkludi bits multipli.

517
00:24:06,610 --> 00:24:10,510
Ejja ngħidu li dan huwa 0 u 1,
mazz sħiħ ta 0s u 1s.

518
00:24:10,510 --> 00:24:11,660
Allura dan huwa hard drive kollu tiegħi.

519
00:24:11,660 --> 00:24:13,225
Din hija apparentement fajl pretty big.

520
00:24:13,225 --> 00:24:18,080
U qed tuża l-0s u 1s f'dak
porzjon tal-platter fiżika.

521
00:24:18,080 --> 00:24:19,750
>> Ukoll, dak li huwa dak il-porzjon fiżika?

522
00:24:19,750 --> 00:24:25,310
Ukoll, jirriżulta li fuq hard drive,
inqas ta 'dan it-tip, hemm

523
00:24:25,310 --> 00:24:27,340
dawn il-partiċelli manjetiċi ċkejkna ftit.

524
00:24:27,340 --> 00:24:32,630
U huma essenzjalment ikollhom tramuntana u
poli nofsinhar għalihom, b'tali mod li jekk inti

525
00:24:32,630 --> 00:24:35,710
dawran wieħed minn dawk partiċelli manjetiċi
B'dan il-mod, inti jista 'jgħid li huwa

526
00:24:35,710 --> 00:24:36,720
jirrappreżentaw 1.

527
00:24:36,720 --> 00:24:39,340
U jekk huwa rasu 'l isfel fin-nofsinhar sa
tramuntana, inti jista 'jgħid li huwa

528
00:24:39,340 --> 00:24:40,390
jirrappreżentaw 0.

529
00:24:40,390 --> 00:24:43,660
>> Allura fid-dinja fiżika reali, li l-
kif inti tista 'tirrappreżenta xi ħaġa

530
00:24:43,660 --> 00:24:45,670
istat binarja tal-0 u 1.

531
00:24:45,670 --> 00:24:46,720
Allura li kollox fajl huwa.

532
00:24:46,720 --> 00:24:49,300
Hemm mazz sħiħ ta 'manjetiċi
partiċelli li huma b'dan il-mod jew tagħhom

533
00:24:49,300 --> 00:24:51,920
b'dan il-mod, il-ħolqien mudelli
ta 0s u 1s.

534
00:24:51,920 --> 00:24:56,760
>> Iżda jirriżulta meta inti tiffranka fajl,
xi informazzjoni jiġi ffrankat separatament.

535
00:24:56,760 --> 00:25:00,000
Allura dan huwa tabella ftit,
direttorju, biex ngħidu hekk.

536
00:25:00,000 --> 00:25:05,810
U jien ser sejħa dan l-isem kolonna, u
I ser sejħa dan il-post kolonna.

537
00:25:05,810 --> 00:25:08,850
>> U jien se ngħid, ejja ngħidu
dan huwa jerġa tiegħi.

538
00:25:08,850 --> 00:25:14,050
Resume.doc tiegħi huwa maħżun
post, ejja ngħidu 123.

539
00:25:14,050 --> 00:25:15,390
I dejjem tmur għall dak in-numru.

540
00:25:15,390 --> 00:25:18,810
Iżda huwa biżżejjed li jingħad li eżatt bħal
fl RAM, inti tista 'tieħu hard drive

541
00:25:18,810 --> 00:25:22,350
Li l-gigabyte jew 200 gigabytes
jew terabyte, u inti tista '

542
00:25:22,350 --> 00:25:23,750
Numru kollha tal-bytes.

543
00:25:23,750 --> 00:25:26,480
Tista jinnumera biċċiet kollha ta '8 bits.

544
00:25:26,480 --> 00:25:29,030
>> Allura aħna ser jgħidu li dan
hija 123 post.

545
00:25:29,030 --> 00:25:32,070
Allura dan ġewwa direttorju ta operattiva tiegħi
sistema jiftakar li tiegħi

546
00:25:32,070 --> 00:25:34,250
jerġa hija fil-post 123.

547
00:25:34,250 --> 00:25:36,850
Iżda jiġrilha interessanti meta
inti tħassar fajl.

548
00:25:36,850 --> 00:25:37,820
>> Allura per eżempju -

549
00:25:37,820 --> 00:25:40,790
u Thankfully, ħafna mill-dinja għandha
maqbuda fuq dan - dak li jiġri meta

550
00:25:40,790 --> 00:25:45,040
inti drag fajl lill Mac OS Trash tiegħek
jew tiegħek Windows Recycle Bin?

551
00:25:45,040 --> 00:25:48,290

552
00:25:48,290 --> 00:25:50,510
X'hemm l-iskop li jagħmlu dan?

553
00:25:50,510 --> 00:25:53,860
Huwa ovvjament biex jeħles mill-fajl,
imma dak ma l-att ta 'jittrattienu u

554
00:25:53,860 --> 00:25:57,550
twaqqa fis Trash tiegħek jew tiegħek
Recycle Bin do fuq kompjuter?

555
00:25:57,550 --> 00:25:59,230
>> Assolutament xejn, verament.

556
00:25:59,230 --> 00:26:00,320
Huwa biss bħal folder.

557
00:26:00,320 --> 00:26:01,800
Huwa folder speċjali, li jkun żgur.

558
00:26:01,800 --> 00:26:04,460
Iżda din hija attwalment iħassar il-fajl?

559
00:26:04,460 --> 00:26:06,780
>> Well, no, għaliex xi wħud minnkom probabbilment
kienu simili, oh kkritikat, inti ma

560
00:26:06,780 --> 00:26:07,420
jfissirx li tagħmel dan.

561
00:26:07,420 --> 00:26:09,130
Allura inti ikklikkja darbtejn l-
Trash jew Recycle Bin.

562
00:26:09,130 --> 00:26:11,630
You ħadthom poked madwar u inti stajt rkuprati
l-fajl biss billi jittrattienu

563
00:26:11,630 --> 00:26:12,110
minn hemmhekk.

564
00:26:12,110 --> 00:26:14,420
Allura ċar, mhuwiex neċessarjament
it-tħassir.

565
00:26:14,420 --> 00:26:15,990
>> OK, int intelliġenti minn dik.

566
00:26:15,990 --> 00:26:18,860
Inti taf li sempliċiment jittrattienu hija fil-
Trash jew Recycle Bin ma jfissirx

567
00:26:18,860 --> 00:26:19,930
int jitbattal il-Trash.

568
00:26:19,930 --> 00:26:24,110
Allura inti tmur sa l-menu, u inti tgħidli
Trash vojta jew vojta Recycle Bin.

569
00:26:24,110 --> 00:26:25,360
Imbagħad x'jiġri?

570
00:26:25,360 --> 00:26:29,070

571
00:26:29,070 --> 00:26:32,530
>> Yeah, għalhekk jitħassar aktar hekk.

572
00:26:32,530 --> 00:26:37,660
Imma dak kollu li jiġri huwa dan.

573
00:26:37,660 --> 00:26:45,350
Il-kompjuter jinsa fejn
resume.doc kien.

574
00:26:45,350 --> 00:26:47,400
>> Imma dak ma nbidlitx apparentement
fl-istampa?

575
00:26:47,400 --> 00:26:51,390

576
00:26:51,390 --> 00:26:55,570
Il-bits, il-0s u 1s li I jsostnu li huma
fuq is-sit ta 'xi aspett fiżiku tal

577
00:26:55,570 --> 00:26:56,280
l-hardware.

578
00:26:56,280 --> 00:26:57,110
Huma qed għadhom hemm.

579
00:26:57,110 --> 00:26:58,930
Huwa biss il-kompjuter għandu
minsija dak li huma.

580
00:26:58,930 --> 00:27:03,160
>> Allura huwa essenzjalment meħlusa tal-fajl
bits sabiex ikunu jistgħu jerġgħu jintużaw.

581
00:27:03,160 --> 00:27:06,940
Iżda mhux sa inti toħloq fajls aktar,
u fajls aktar, u aktar fajls se

582
00:27:06,940 --> 00:27:12,150
probabilistically, dawk 0s u 1s,
dawk partiċelli manjetiċi, nikseb jerġgħu jintużaw,

583
00:27:12,150 --> 00:27:16,220
naħa rasu jew dritt up, għal
fajls oħra, 0s u 1s.

584
00:27:16,220 --> 00:27:17,980
>> Allura inti għandek il-tieqa ta 'żmien.

585
00:27:17,980 --> 00:27:19,860
U m'humiex ta prevedibbli
tul, verament.

586
00:27:19,860 --> 00:27:22,240
Hija tiddependi fuq id-daqs tal-hard tiegħek
drive u fajls kemm għandek u

587
00:27:22,240 --> 00:27:23,490
kif malajr inti tagħmel oħrajn ġodda.

588
00:27:23,490 --> 00:27:27,050
Iżda hemm dan iż-żmien matul
li dan il-fajl għadu perfettament

589
00:27:27,050 --> 00:27:27,770
jistgħux jitħallsu lura.

590
00:27:27,770 --> 00:27:31,050
>> Mela jekk inti qatt tuża programmi bħal McAfee
jew Norton biex jippruvaw jirkupraw

591
00:27:31,050 --> 00:27:35,680
data, kollha li qed isir qed tipprova
jirkupraw dan id-direttorju hekk imsejħa biex

592
00:27:35,680 --> 00:27:37,340
insemmu fejn fajl tiegħek kienet.

593
00:27:37,340 --> 00:27:40,605
U xi kultant Norton u se ngħid,
fajl huwa 93% jitħallsu lura.

594
00:27:40,605 --> 00:27:42,020
Well, dak ma jfisser?

595
00:27:42,020 --> 00:27:45,690
Dan ifisser biss li xi fajl ieħor
inzerta spiċċaw użu, ngħidu aħna,

596
00:27:45,690 --> 00:27:48,920
dawk bits barra tal-fajl oriġinali tiegħek.

597
00:27:48,920 --> 00:27:51,950
>> Allura dak li huwa attwalment involut
fl-irkupru tad-data?

598
00:27:51,950 --> 00:27:55,720
Ukoll, jekk inti ma għandekx xi ħaġa bħal
Norton installat minn qabel fuq il-kompjuter tiegħek,

599
00:27:55,720 --> 00:27:59,510
l-aħjar inti xi kultant tista 'tagħmel hu li tħares
fil-hard drive kollu tfittex

600
00:27:59,510 --> 00:28:00,510
mudelli ta 'bits.

601
00:28:00,510 --> 00:28:05,350
U waħda mit-temi ta 'problema sett
ħamsa li inti se tfittex il-

602
00:28:05,350 --> 00:28:09,570
ekwivalenti ta 'hard drive, a forensika
immaġni ta 'karta flash kompatti minn

603
00:28:09,570 --> 00:28:13,660
kamera diġitali, it-tiftix għall-0s
u 1s li tipikament, ma għolja

604
00:28:13,660 --> 00:28:16,720
probabbiltà, jirrappreżentaw il-
bidu ta 'immaġni JPEG.

605
00:28:16,720 --> 00:28:21,120
>> U inti guys jistgħu jirkupraw dawk l-immaġini minn
jekk wieħed jassumi, jekk nara dan il-mudell ta '

606
00:28:21,120 --> 00:28:24,380
bits fuq l-immaġni forensika, bil
probabbiltà għolja, li l-marki

607
00:28:24,380 --> 00:28:25,650
il-bidu ta 'JPEG.

608
00:28:25,650 --> 00:28:29,520
U jekk nara l-istess mudell mill-ġdid,
li probabbilment jimmarka l-bidu ta '

609
00:28:29,520 --> 00:28:32,440
ieħor JPEG, u ieħor
JPEG, JPEG u ieħor.

610
00:28:32,440 --> 00:28:34,970
U dan huwa tipikament kif
data ta 'rkupru se taħdem.

611
00:28:34,970 --> 00:28:37,870
X'hemm sbieħ dwar JPEGs huwa anke jekk
il-format tal-fajl nnifisha hija kemmxejn

612
00:28:37,870 --> 00:28:44,400
kumplessi, il-bidu ta 'kull tali
fajl huwa attwalment pjuttost identifikabbli

613
00:28:44,400 --> 00:28:47,370
u sempliċi, kif se tara,
Jekk inti stajt ma diġà.

614
00:28:47,370 --> 00:28:50,270
>> Mela ejja tagħti ħarsa aktar mill-qrib taħt
il-barnuża dwar eżattament dak li kien

615
00:28:50,270 --> 00:28:53,360
għaddejjin, u liema dawn 0s u 1s
huma, li jtik daqsxejn aktar ta '

616
00:28:53,360 --> 00:28:55,330
kuntest għal din l-isfida partikolari.

617
00:28:55,330 --> 00:28:55,510
>> [Daqq video]

618
00:28:55,510 --> 00:28:58,700
>> Fejn PC tiegħek-ħwienet l-aktar
ta 'data permanenti tagħha.

619
00:28:58,700 --> 00:29:03,390
Biex tagħmel dan, l-informazzjoni jivvjaġġa minn RAM
flimkien ma 'sinjali ta' softwer li jgħidulek

620
00:29:03,390 --> 00:29:06,110
l-hard drive kif jaħżnu dik id-data.

621
00:29:06,110 --> 00:29:09,410
Iċ-ċirkwiti hard drive tittraduċi
dawk is-sinjali fi vultaġġ

622
00:29:09,410 --> 00:29:10,870
varjazzjonijiet.

623
00:29:10,870 --> 00:29:14,970
Dawn, imbagħad, jikkontrollaw il-drive hard
partijiet li jiċċaqalqu, xi wħud mill-ftit

624
00:29:14,970 --> 00:29:17,910
partijiet li jiċċaqalqu jitħalla fil-
moderni tal-kompjuter.

625
00:29:17,910 --> 00:29:22,130
>> Uħud mill-sinjali tal-kontroll bil-mutur
li spins platters metall miksija.

626
00:29:22,130 --> 00:29:25,470
Id-data tiegħek huwa attwalment maħżuna
fuq dawn platters.

627
00:29:25,470 --> 00:29:28,610
Sinjali oħra li jiċċaqalqu l-taqra / tikteb
irjus biex taqra jew

628
00:29:28,610 --> 00:29:30,710
jikteb data dwar il-platters.

629
00:29:30,710 --> 00:29:35,450
Dan makkinarju tant preċiżi li bniedem
xagħar ma setgħux lanqas tgħaddi bejn il-

630
00:29:35,450 --> 00:29:37,280
irjus u platti għażil.

631
00:29:37,280 --> 00:29:40,316
Madankollu, hija taħdem kollha b'veloċità terrific.

632
00:29:40,316 --> 00:29:40,660
>> [Daqq video END]

633
00:29:40,660 --> 00:29:42,190
>> DAVID Malan: Zoom fi ftit
aktar profonda issa fil x'hemm

634
00:29:42,190 --> 00:29:44,360
attwalment fuq dawk platters.

635
00:29:44,360 --> 00:29:44,720
>> [Daqq video]

636
00:29:44,720 --> 00:29:47,660
>> -Ejja nħarsu lejn dak li aħna biss
raw fil-mozzjoni bil-mod.

637
00:29:47,660 --> 00:29:51,710
Meta polz qasira ta 'l-elettriku huwa
mibgħuta lill-taqra / tikteb ras, jekk Flips

638
00:29:51,710 --> 00:29:54,650
fuq elettromanjetika ċkejkna għal
frazzjoni ta 'sekonda.

639
00:29:54,650 --> 00:29:58,970
Il-kalamita joħloq qasam, li
bidliet l-polarità ta 'ċkejkna, ċkejkna

640
00:29:58,970 --> 00:30:02,850
porzjon tal-partikoli tal-metall li
coat kull wiċċ platter.

641
00:30:02,850 --> 00:30:05,940
>> Serje mudell ta 'dawn ċkejkna,
oqsma ċċarġjati up fuq il-disk

642
00:30:05,940 --> 00:30:08,470
jirrappreżenta ftit uniku ta '
data fin-numru binarju

643
00:30:08,470 --> 00:30:10,530
sistema użata mill-kompjuters.

644
00:30:10,530 --> 00:30:13,775
Issa, jekk il-kurrent tintbagħat mod wieħed
permezz tal-taqra / tikteb ras, iż-żona

645
00:30:13,775 --> 00:30:15,970
ikun polarizzat f'direzzjoni waħda.

646
00:30:15,970 --> 00:30:17,950
Jekk l-kurrent tintbagħat fil-
direzzjoni opposta, il-

647
00:30:17,950 --> 00:30:19,930
polarizzazzjoni hija maqluba.

648
00:30:19,930 --> 00:30:22,370
>> Kif inti tikseb off data l-hard disk?

649
00:30:22,370 --> 00:30:24,090
Just jitwaqqaf il-proċess.

650
00:30:24,090 --> 00:30:26,550
Allura huwa l-partiċelli fuq il-disk
li jiksbu l-kurrent fil-

651
00:30:26,550 --> 00:30:27,960
taqra / tikteb ras li jiċċaqalqu.

652
00:30:27,960 --> 00:30:30,700
Poġġi flimkien miljuni ta 'dawn
segmenti magnetized, u

653
00:30:30,700 --> 00:30:32,160
inti stajt ltqajna fajl.

654
00:30:32,160 --> 00:30:36,060
>> Issa, il-biċċiet ta 'fajl waħdieni jistgħu
jiġu imxerrda fuq l-drive

655
00:30:36,060 --> 00:30:39,970
platters, tip ta bħall-mess
ta 'dokumenti dwar iskrivanija tiegħek.

656
00:30:39,970 --> 00:30:43,500
Allura fajl extra speċjali iżomm rekord
ta 'fejn kollox huwa.

657
00:30:43,500 --> 00:30:45,985
Ma inti tixtieq kellhom
xi ħaġa bħal dik?

658
00:30:45,985 --> 00:30:46,470
>> [Daqq video END]

659
00:30:46,470 --> 00:30:47,820
>> DAVID Malan: OK, probabbilment le.

660
00:30:47,820 --> 00:30:52,070
Allura kif ħafna minnkom guys
kiber ma 'dawn?

661
00:30:52,070 --> 00:30:53,970
OK, dan huwa inqas u inqas
idejn kull sena.

662
00:30:53,970 --> 00:30:56,550
Imma jien kuntenta int inqas familjari
magħhom, minħabba dan u tagħna stess

663
00:30:56,550 --> 00:31:00,520
demo ktieb, sfortunatament, qegħdin imutu ħafna
bil-mod mewt hawn 'familjarità.

664
00:31:00,520 --> 00:31:04,010
>> Imma dan huwa dak I, għall-inqas, lura fl-
iskola għolja, l-użu użati għall-backups.

665
00:31:04,010 --> 00:31:08,110
U kien aqwa, għaliex inti
jista 'jaħżen 1.4 megabytes fuq

666
00:31:08,110 --> 00:31:08,930
dan disk partikolari.

667
00:31:08,930 --> 00:31:12,260
U dan kien il-verżjoni densità għolja,
kif indikat mill-HD, li għandha

668
00:31:12,260 --> 00:31:14,240
jiġifieri qabel videos HD lum.

669
00:31:14,240 --> 00:31:16,400
>> Densità Standard kienet ta '800 kilobytes.

670
00:31:16,400 --> 00:31:18,640
U qabel li, kien hemm
Diski 400-kilobyte.

671
00:31:18,640 --> 00:31:23,120
U qabel li, kien hemm 5 u 1/4
pulzier diski, li kienu tassew floppy,

672
00:31:23,120 --> 00:31:25,680
u ftit usa 'u taller
minn dawn l-affarijiet hawn.

673
00:31:25,680 --> 00:31:29,150
Iżda int tista 'attwalment ara l-hekk imsejħa
Aspett floppy disks ta 'dawn.

674
00:31:29,150 --> 00:31:32,630
>> U funzjonalment, dawn qed attwalment
pretty simili għal hard drives ta 'mill-

675
00:31:32,630 --> 00:31:33,570
inqas dan it-tip.

676
00:31:33,570 --> 00:31:37,270
Għal darb'oħra, SSDs fil-kompjuters ġodda
jaħdmu ftit differenti.

677
00:31:37,270 --> 00:31:41,530
Imma jekk inti tmur li tab metall ftit,
inti tista 'attwalment tara cookie ftit,

678
00:31:41,530 --> 00:31:42,560
jew platter.

679
00:31:42,560 --> 00:31:43,830
>> Mhuwiex metall bħal dan wieħed.

680
00:31:43,830 --> 00:31:46,000
Dan wieħed fil-fatt xi irħas
materjal tal-plastik.

681
00:31:46,000 --> 00:31:46,750
U inti tista 'tip ta' wiggle.

682
00:31:46,750 --> 00:31:50,310
U inti stajt biss trully mimsuħ off xi
numru ta 'bits jew partiċelli manjetiċi

683
00:31:50,310 --> 00:31:51,220
minn dan disk.

684
00:31:51,220 --> 00:31:52,710
>> Allura Thankfully, hemm xejn fuqha.

685
00:31:52,710 --> 00:31:55,790
Jekk dik ħaġa fil-mod - u jkopru
għajnejn tiegħek u dawk tal-proxxmu tiegħek -

686
00:31:55,790 --> 00:31:58,865
inti tista 'biss tip ta' tiġbed dan
off għant kollu bħal dik.

687
00:31:58,865 --> 00:32:01,900
Iżda hemm rebbiegħa ftit, sabiex ikunu
konxji ta 'dak mal-għajnejn tiegħek.

688
00:32:01,900 --> 00:32:03,620
Allura issa għandek verament floppy disk.

689
00:32:03,620 --> 00:32:07,090
>> U x'hemm notevoli dwar din
hija li fil kemm dan huwa

690
00:32:07,090 --> 00:32:10,830
rappreżentazzjoni fuq skala żgħira ta 'akbar
hard drive, dawn l-affarijiet huma super,

691
00:32:10,830 --> 00:32:11,590
sempliċi super.

692
00:32:11,590 --> 00:32:15,170
Jekk inti oqros il-qiegħ ta 'dan, issa li
li ħaġa metall huwa off, u l-qoxra

693
00:32:15,170 --> 00:32:20,990
minnhom miftuħa, kollha hemm hi ta 'żewġ biċċiet ta'
feltru u l-hekk imsejħa disk floppy

694
00:32:20,990 --> 00:32:22,930
ma 'biċċa ta' metall fuq ġewwa.

695
00:32:22,930 --> 00:32:25,990
>> U hemm tmur nofs
kontenut disk tiegħi.

696
00:32:25,990 --> 00:32:27,540
Hemm tmur ieħor nofs minnhom.

697
00:32:27,540 --> 00:32:31,375
Imma dak li kollu li kien għażil ġewwa
tal-kompjuter tiegħek fl-imgħoddi.

698
00:32:31,375 --> 00:32:35,220

699
00:32:35,220 --> 00:32:38,310
>> U għal darb'oħra, dan iseħħ fil-perspettiva,
kemm hu kbir huwa l-aktar ta 'tiegħek

700
00:32:38,310 --> 00:32:39,560
hard drives dawn il-jiem?

701
00:32:39,560 --> 00:32:41,960

702
00:32:41,960 --> 00:32:46,230
500 gigabytes, terabyte, forsi fl
kompjuter desktop, 2 terabytes, 3

703
00:32:46,230 --> 00:32:47,630
terabytes, 4 ta'Terabytes, id-dritt?

704
00:32:47,630 --> 00:32:52,480
Dan huwa megabyte wieħed, jagħtu jew jieħu,
li ma jistgħux anki jitwaħħal MP3 tipiku

705
00:32:52,480 --> 00:32:55,310
jibqgħalu dawn il-jiem, jew xi
mużika fajl simili.

706
00:32:55,310 --> 00:32:59,500
>> Allura tifkira ftit għalik illum, u
wkoll biex jgħin contextualize dak

707
00:32:59,500 --> 00:33:03,570
aħna ser tkun qed tieħu għall mogħtija
issa problema stabbiliti ħamsa.

708
00:33:03,570 --> 00:33:04,820
Għalhekk dawn huma tiegħek li żżomm.

709
00:33:04,820 --> 00:33:07,340

710
00:33:07,340 --> 00:33:13,370
So let me tranżizzjoni fejn se jkun
l-infiq l pset jmiss ukoll.

711
00:33:13,370 --> 00:33:18,470
Allura aħna ħadthom issa stabbilit din il-paġna għall - oh,
koppja ta 'avviżi malajr.

712
00:33:18,470 --> 00:33:21,730
>> Dan Ġimgħa, jekk inti tixtieq jissieħbu CS50
għall-ikel, mur l-post tas-soltu,

713
00:33:21,730 --> 00:33:23,610
cs50.net/rsvp.

714
00:33:23,610 --> 00:33:25,100
U proġett finali -

715
00:33:25,100 --> 00:33:28,520
hekk kull-sillabu, konna stazzjonati l-
ispeċifikazzjoni tal-proġett finali diġà.

716
00:33:28,520 --> 00:33:31,410
Jirrealizzaw li dan ma jfissirx
huwa dovut partikolarment dalwaqt.

717
00:33:31,410 --> 00:33:33,990
Huwa stazzjonati, verament, biss li tikseb
inti guys taħseb dwar dan.

718
00:33:33,990 --> 00:33:37,620
U tabilħaqq, super sinifikanti
persentaġġ ta 'inti tkun indirizzar

719
00:33:37,620 --> 00:33:40,780
proġetti finali dwar materjal li aħna
lanqas biss gotten fil-klassi,

720
00:33:40,780 --> 00:33:42,730
iżda se kmieni kemm ġimgħa d-dieħla.

721
00:33:42,730 --> 00:33:45,530
>> Avviż, madankollu, li l-spec jitlob
xi komponenti differenti ftit tal-

722
00:33:45,530 --> 00:33:46,190
proġett finali.

723
00:33:46,190 --> 00:33:49,590
L-ewwel, fi ftit ġimgħat, huwa
pre-proposta, email pretty każwali biex

724
00:33:49,590 --> 00:33:52,760
TF tiegħek li tgħid lilu jew dak li int
taħseb dwar għall-proġett tiegħek, ma

725
00:33:52,760 --> 00:33:53,650
ebda impenn.

726
00:33:53,650 --> 00:33:56,710
Proposta se jkun partikolari tiegħek
impenn, qal, hawnhekk, dan huwa dak

727
00:33:56,710 --> 00:33:57,770
I tixtieq tagħmel għall-proġett tiegħi.

728
00:33:57,770 --> 00:33:58,250
What do you think?

729
00:33:58,250 --> 00:33:58,650
Kbira wisq?

730
00:33:58,650 --> 00:33:59,145
Żgħir wisq?

731
00:33:59,145 --> 00:34:00,330
Huwa maniġġabbli?

732
00:34:00,330 --> 00:34:02,230
U tara l-spec għal aktar dettalji.

733
00:34:02,230 --> 00:34:05,060
>> Koppja ta 'ġimgħat wara li l-istatus
rapport, li huwa simili

734
00:34:05,060 --> 00:34:08,260
email każwali biex TF tiegħek li tgħid kemm
ferm lura inti fil finali tiegħek

735
00:34:08,260 --> 00:34:12,360
implimentazzjoni proġett, segwit minn
l-Hackathon CS50 li għalihom kulħadd

736
00:34:12,360 --> 00:34:17,520
huwa mistieden, li se jkun avveniment minn
20:00 fuq waħda filgħaxija till 07:00

737
00:34:17,520 --> 00:34:19,150
AM l-għada filgħodu.

738
00:34:19,150 --> 00:34:22,560
Pizza, kif I jista 'jkollhom imsemmija fil-ġimgħa
żero, wil jkun innotifikat fil 09:00,

739
00:34:22,560 --> 00:34:24,120
Ikel Ċiniż fil 01:00.

740
00:34:24,120 --> 00:34:27,929
U jekk int xorta imqajjem fi 5:00 AM,
aħna ser tieħdok għall IHOP għall-kolazzjon.

741
00:34:27,929 --> 00:34:31,310
>> Allura l-Hackathon hija waħda mill-aktar
esperjenzi memorabbli fil-klassi.

742
00:34:31,310 --> 00:34:35,290
Imbagħad l-implimentazzjoni huwa dovut, u
allura l-climactic CS50 Fair.

743
00:34:35,290 --> 00:34:38,070
Aktar dettalji dwar dawn kollha
fil-ġimgħat li ġejjin.

744
00:34:38,070 --> 00:34:40,739
>> Imma ejja mmorru lura għal xi ħaġa
iskola antika -

745
00:34:40,739 --> 00:34:41,920
għal darb'oħra, firxa.

746
00:34:41,920 --> 00:34:45,040
Allura firxa kien sbieħ, minħabba li jsolvi
problemi bħal rajna biss

747
00:34:45,040 --> 00:34:49,290
mument ilu bi strutturi student
jkollna ftit mill-kontroll jekk aħna

748
00:34:49,290 --> 00:34:52,405
jridu li jkollhom student wieħed, student tnejn,
student tlieta, student dot dot dot,

749
00:34:52,405 --> 00:34:54,400
xi numru arbitrarju ta 'studenti.

750
00:34:54,400 --> 00:34:58,850
>> Allura arrays, ftit ġimgħat ilu, swooped fl
u solvuti l-problemi tagħna ta 'mhux

751
00:34:58,850 --> 00:35:03,340
jafu bil-quddiem affarijiet kemm
ta 'xi tip aħna tista' tixtieq.

752
00:35:03,340 --> 00:35:07,390
U Rajna li structs tista 'tgħinna
aktar torganizza kodiċi tagħna u jżommu

753
00:35:07,390 --> 00:35:11,660
varjabbli kunċettwalment simili, bħal
isem u dar, flimkien, sabiex inkunu

754
00:35:11,660 --> 00:35:15,570
jistgħu jittrattawhom bħala entità waħda, ġewwa
li minnhom hemm biċċiet iżgħar.

755
00:35:15,570 --> 00:35:17,810
>> Iżda arrays jkollhom xi żvantaġġi.

756
00:35:17,810 --> 00:35:19,780
Liema huma wħud mill-iżvantaġġi
konna jiltaqgħu magħhom

757
00:35:19,780 --> 00:35:22,320
ma arrays s'issa?

758
00:35:22,320 --> 00:35:23,450
X'hemm li?

759
00:35:23,450 --> 00:35:28,130
Daqs fiss - hekk anke jekk inti tista '
tkun tista 'talloka memorja għal

760
00:35:28,130 --> 00:35:32,310
array, ladarba inti taf kif ħafna studenti
ikollok, kemm karattri għandek

761
00:35:32,310 --> 00:35:35,460
mill-utent, ladarba inti stajt allokati
il-firxa, inti stajt tip ta 'miżbugħa

762
00:35:35,460 --> 00:35:36,740
lilek innifsek fis-kantuniera.

763
00:35:36,740 --> 00:35:40,600
>> Għaliex inti ma tista 'daħħal elementi ġodda
fis-nofs ta 'firxa.

764
00:35:40,600 --> 00:35:43,660
Inti ma tistax daħħal elementi aktar
fl-aħħar ta 'firxa.

765
00:35:43,660 --> 00:35:47,750
Really, inti jkollhom jirrikorru għal ħolqien ta '
firxa sħiħa ġdida, kif konna diskussi,

766
00:35:47,750 --> 00:35:49,320
ikkupjar l-qodma fil-ġdida.

767
00:35:49,320 --> 00:35:52,610
U għal darb'oħra, dan huwa l-uġigħ ta 'ras li
GetString jittratta għalik.

768
00:35:52,610 --> 00:35:56,170
>> Iżda għal darb'oħra, inti ma tistax anki daħħal
xi ħaġa fis-nofs tal-firxa

769
00:35:56,170 --> 00:35:58,200
jekk ir-rata ma tkunx ġiet mimlija kompletament.

770
00:35:58,200 --> 00:36:03,010
Per eżempju, jekk dan array hawn ta 'daqs
sitta biss għandha ħames affarijiet fiha,

771
00:36:03,010 --> 00:36:06,080
ukoll, inti tista 'biss tindi
xi ħaġa fuq l-aħħar.

772
00:36:06,080 --> 00:36:08,200
Imma x'jiġri jekk inti tixtieq li daħħal xi ħaġa
fis-nofs ta 'l-

773
00:36:08,200 --> 00:36:11,280
array, anki jekk jista 'jkollhom
ħamsa mis-sitt affarijiet fih?

774
00:36:11,280 --> 00:36:14,250
>> Ukoll, dak li ma nagħmlu meta kellna kollha
ta 'voluntiera umani tagħna onstage fil

775
00:36:14,250 --> 00:36:15,110
ġimgħat passat?

776
00:36:15,110 --> 00:36:18,710
Jekk ridna li tpoġġi xi ħadd hawnhekk, jew
dawn in-nies kif jimxu dan

777
00:36:18,710 --> 00:36:22,540
mod, jew dawn in-nies kif jimxu dan
mod, u li saret għalja.

778
00:36:22,540 --> 00:36:26,950
Ċ-ċaqliq tan-nies ġewwa ta '
array spiċċaw żżid up u jiswew

779
00:36:26,950 --> 00:36:31,240
us ħin, għalhekk ħafna kwadrat n tagħna
running żminijiet bħal sort inserzjoni, per

780
00:36:31,240 --> 00:36:32,550
Pereżempju, fl-agħar każ.

781
00:36:32,550 --> 00:36:36,520
Allura arrays huma kbar, iżda inti għandek
taf minn qabel kemm hu kbir inti tixtieq.

782
00:36:36,520 --> 00:36:38,030
>> Allura OK, hawnhekk soluzzjoni.

783
00:36:38,030 --> 00:36:43,860
Jekk jien ma jaf minn qabel kemm
studenti I jista 'jkollhom, u naf ladarba

784
00:36:43,860 --> 00:36:47,870
I jiddeċiedu, għalkemm, jien mwaħħla ma 'dik
ħafna studenti, għaliex ma I biss dejjem

785
00:36:47,870 --> 00:36:51,740
jallokaw darbtejn ħafna spazju
kif I tista 'taħseb I bżonn?

786
00:36:51,740 --> 00:36:54,450
Hija li mhux soluzzjoni raġonevoli?

787
00:36:54,450 --> 00:36:58,240
>> Realistikament, ma naħsibx li aħna qed
ser jeħtieġu aktar minn 50 slots

788
00:36:58,240 --> 00:37:02,190
fil-firxa għall-klassi ta 'daqs medju,
hekk ejja biss madwar up.

789
00:37:02,190 --> 00:37:07,040
I ser tagħmel 100 slots fl array tiegħi, biss
sabiex inkunu nistgħu definittivament jiksbu l-

790
00:37:07,040 --> 00:37:10,330
numru ta 'studenti I tistenna li
jkun f'xi klassi ta 'daqs medju.

791
00:37:10,330 --> 00:37:14,320
Allura għaliex mhux biss jarrotondaw u jallokaw
memorja aktar, tipikament, għal firxa

792
00:37:14,320 --> 00:37:16,290
milli taħseb inti tista 'anki bżonn?

793
00:37:16,290 --> 00:37:20,190
X'hemm dan pushback sempliċi
għal dik l-idea?

794
00:37:20,190 --> 00:37:21,440
>> Int biss wasting memorja.

795
00:37:21,440 --> 00:37:25,350
Litteralment kull programm tikteb mbagħad
huwa forsi tuża memorja doppju ta 'kemm

796
00:37:25,350 --> 00:37:26,680
inti fil-fatt bżonn.

797
00:37:26,680 --> 00:37:28,990
U li biss ma jħossu bħal
partikolarment soluzzjoni eleganti.

798
00:37:28,990 --> 00:37:31,990
Barra minn hekk, hija biss inaqqas l-
probabbiltà ta 'problema.

799
00:37:31,990 --> 00:37:35,300
Jekk jiġri li jkollhom kors popolari
semestru wieħed u inti għandek 101

800
00:37:35,300 --> 00:37:39,610
istudenti, program tiegħek għadu
fundamentalment jiffaċċjaw l-istess kwistjoni.

801
00:37:39,610 --> 00:37:44,280
>> Allura Thankfully, hemm soluzzjoni għal
dan ad problemi kollha tagħna fil-forma

802
00:37:44,280 --> 00:37:46,790
ta 'strutturi ta' dejta li huma
aktar kumplessi minn dawk

803
00:37:46,790 --> 00:37:47,970
Rajna s'issa.

804
00:37:47,970 --> 00:37:50,530
Dan, nitlob, hija lista linked.

805
00:37:50,530 --> 00:37:51,920
Din hija lista ta 'numri -

806
00:37:51,920 --> 00:37:54,970
9, 17, 22, 26, u 34 -

807
00:37:54,970 --> 00:38:00,120
li ġew marbuta flimkien permezz
ta 'dak li stajt mfassla bħala vleġeġ.

808
00:38:00,120 --> 00:38:03,580
>> Fi kliem ieħor, jekk jien ridt li jirrappreżentaw
firxa, I tista 'tagħmel

809
00:38:03,580 --> 00:38:04,910
xi ħaġa bħal din.

810
00:38:04,910 --> 00:38:07,310
U jien ser tpoġġi dan fuq il-overhead
fi ftit mument.

811
00:38:07,310 --> 00:38:09,970
I tista 'tagħmel -

812
00:38:09,970 --> 00:38:12,520
hello, id-dritt.

813
00:38:12,520 --> 00:38:14,470
Stand mill.

814
00:38:14,470 --> 00:38:17,360
Kompjuter ġdid hawn, ċari -

815
00:38:17,360 --> 00:38:18,090
id-dritt.

816
00:38:18,090 --> 00:38:21,730
>> Mela jekk ikolli dawn in-numri fil-firxa -

817
00:38:21,730 --> 00:38:28,880
9, 17, 22, 26, 24 -

818
00:38:28,880 --> 00:38:30,530
mhux neċessarjament l-iskala.

819
00:38:30,530 --> 00:38:33,730
Kull dritt, hekk hawn huwa firxa tiegħi -

820
00:38:33,730 --> 00:38:34,980
oh my god.

821
00:38:34,980 --> 00:38:38,700

822
00:38:38,700 --> 00:38:40,395
Kull dritt, hekk hawn huwa firxa tiegħi.

823
00:38:40,395 --> 00:38:44,110

824
00:38:44,110 --> 00:38:45,050
Oh my god.

825
00:38:45,050 --> 00:38:48,820
>> [Daħk]

826
00:38:48,820 --> 00:38:49,440
>> DAVID Malan: nippretendu.

827
00:38:49,440 --> 00:38:52,330
Huwa wisq sforz biex tmur lura
u tiffissa li, hekk hemm -

828
00:38:52,330 --> 00:38:54,290
26.

829
00:38:54,290 --> 00:38:57,650
Allura aħna għandna dan firxa ta '
9, 17, 22, 26, u 34.

830
00:38:57,650 --> 00:39:00,260
Għal dawk tal inti tista 'tara l-
żball imbarazzanti I biss magħmula,

831
00:39:00,260 --> 00:39:00,830
hemm hu.

832
00:39:00,830 --> 00:39:04,490
>> So I jsostnu li din hija
soluzzjoni effiċjenti ħafna.

833
00:39:04,490 --> 00:39:07,310
Stajt allokati kif ħafna ints kif
I bżonn - wieħed, tnejn, tlieta,

834
00:39:07,310 --> 00:39:09,100
erba ', ħames, sitt jew -

835
00:39:09,100 --> 00:39:11,660
u stajt mbagħad maħżun-numri
ġewwa ta 'dan array.

836
00:39:11,660 --> 00:39:15,220
Iżda suppose, allura, nixtieq li daħħal
valur bħall-numru 8?

837
00:39:15,220 --> 00:39:16,100
Ukoll, fejn ma tmur?

838
00:39:16,100 --> 00:39:18,530
Jissoponi Irrid li daħħal
numru simili 20.

839
00:39:18,530 --> 00:39:19,790
Ukoll, fejn ma tmur?

840
00:39:19,790 --> 00:39:23,160
X'imkien hemm fin-nofs,
jew in-numru 35 irid imur

841
00:39:23,160 --> 00:39:24,010
x'imkien fl-aħħar.

842
00:39:24,010 --> 00:39:25,320
Imma jien kollha barra ta 'spazju.

843
00:39:25,320 --> 00:39:29,120
>> U għalhekk din hija sfida fundamentali
ta 'arrays li ma huma s-soluzzjoni.

844
00:39:29,120 --> 00:39:32,280
I qal mument ilu, GetString
issolvi din il-problema.

845
00:39:32,280 --> 00:39:37,380
Jekk inti tixtieq li daħħal is-sitt numru
fis dan array, dak li huwa mill-inqas wieħed

846
00:39:37,380 --> 00:39:40,090
soluzzjoni tista 'taqa' lura fuq għall-żgur,
bħad nagħmlu ma GetString?

847
00:39:40,090 --> 00:39:44,340

848
00:39:44,340 --> 00:39:46,030
X'hemm li?

849
00:39:46,030 --> 00:39:48,190
>> Ukoll, jagħmilha akbar huwa
aktar faċli minn qal jsir.

850
00:39:48,190 --> 00:39:52,810
Aħna ma tistax neċessarjament jagħmlu l-firxa
akbar, imma x'nistgħu nagħmlu?

851
00:39:52,810 --> 00:39:56,570
Agħmel firxa ġdida li l-akbar, ta 'daqs
6, jew forsi daqs 10, jekk irridu

852
00:39:56,570 --> 00:40:00,490
biex tikseb l quddiem ta 'affarijiet, u mbagħad kopja
il-firxa qodma fil-ġdida, u mbagħad

853
00:40:00,490 --> 00:40:01,680
ħielsa l array qodma.

854
00:40:01,680 --> 00:40:05,770
>> Imma x'inhu l-running time
issa ta 'dak il-proċess?

855
00:40:05,770 --> 00:40:09,870
Huwa big O ta 'n, minħabba li l-ikkupjar
va ispiża inti xi unitajiet ta '

856
00:40:09,870 --> 00:40:13,480
żmien, sabiex mhux hekk ideali jekk irridu
jallokaw firxa ġdida, li se

857
00:40:13,480 --> 00:40:15,610
li jikkunsmaw darbtejn daqs
memorja temporanjament.

858
00:40:15,610 --> 00:40:16,660
Kopja qodma ġodda -

859
00:40:16,660 --> 00:40:18,800
I mean, huwa biss ras, li
huwa, għal darb'oħra, għaliex aħna kiteb

860
00:40:18,800 --> 00:40:19,920
GetString għalik.

861
00:40:19,920 --> 00:40:21,380
>> Allura dak li jista 'nagħmlu minflok?

862
00:40:21,380 --> 00:40:25,000
Ukoll, dak li jekk l-istruttura tad-data tagħna
attwalment għandha lakuni fil dan?

863
00:40:25,000 --> 00:40:30,790
Ejja ngħidu li I jirrilassaw għan tiegħi ta 'wara
biċċiet kontigwi ta 'memorja, fejn 9

864
00:40:30,790 --> 00:40:34,500
huwa dritt li jmiss għall-17, li huwa
dritt li jmiss għall-22, u l-bqija.

865
00:40:34,500 --> 00:40:39,570
>> U jissoponi li 9 tistax tkun hawn
RAM, u 17 jistgħu jiġu minn hawn fil-RAM,

866
00:40:39,570 --> 00:40:40,990
u 22 jistgħu jiġu minn hawn fil-RAM.

867
00:40:40,990 --> 00:40:43,610
Fi kliem ieħor, I m'għandhomx bżonn minnhom
anki lura lura aktar.

868
00:40:43,610 --> 00:40:47,850
I biss għandhom b'xi mod ħajt labra
permezz kull wieħed minn dawn in-numri, jew kull

869
00:40:47,850 --> 00:40:51,010
ta 'dawn in-nodi, kif aħna ser sejħa-
rettangoli kif stajt mfassla minnhom, lil

870
00:40:51,010 --> 00:40:55,670
tiftakar kif tikseb l-aħħar
bħal node mill-ewwel.

871
00:40:55,670 --> 00:40:59,940
>> Allura x'inhi l-ipprogrammar jinbena
Rajna pjuttost reċentement li jien

872
00:40:59,940 --> 00:41:03,030
tista 'timplimenta dak il-ħajt, jew
mfassla hawn, li nista '

873
00:41:03,030 --> 00:41:05,430
jimplimentaw dawk vleġeġ?

874
00:41:05,430 --> 00:41:06,500
Pointers Allura, id-dritt?

875
00:41:06,500 --> 00:41:09,560
Jekk I jallokaw mhux biss
int, imma node - u billi

876
00:41:09,560 --> 00:41:10,810
node, I jfissirx biss kontenitur.

877
00:41:10,810 --> 00:41:12,900
U viżwalment, I tfisser rettangolu.

878
00:41:12,900 --> 00:41:16,420
Allura node apparentement teħtieġ
li fihom żewġ valuri -

879
00:41:16,420 --> 00:41:21,490
l-int innifsu, u mbagħad, kif implikat
l-nofs ta 'isfel tar-rettangolu,

880
00:41:21,490 --> 00:41:23,010
biżżejjed spazju għal int.

881
00:41:23,010 --> 00:41:26,130
>> Hekk biss jaħsbu quddiem hawnhekk,
kemm hu kbir huwa dan node, dan

882
00:41:26,130 --> 00:41:27,170
kontenitur relattiv?

883
00:41:27,170 --> 00:41:29,250
Kemm bytes għall-int?

884
00:41:29,250 --> 00:41:31,310
Preżumibbilment 4, jekk huwa
l-istess bħas-soltu.

885
00:41:31,310 --> 00:41:33,270
U allura kemm bytes
għall-pointer?

886
00:41:33,270 --> 00:41:33,650
4.

887
00:41:33,650 --> 00:41:37,940
Allura dan il-kontenitur, jew dan node, huwa
ser tkun struttura 8-byte.

888
00:41:37,940 --> 00:41:41,760
Oh, u li l-koinċidenza kuntenti li
aħna biss introduċiet dan il-kunċett ta '

889
00:41:41,760 --> 00:41:44,400
a Struct, jew struttura C.

890
00:41:44,400 --> 00:41:48,890
>> So I jsostnu li nixtieq li tieħu pass
lejn dan aktar sofistikati

891
00:41:48,890 --> 00:41:52,560
implimentazzjoni ta 'lista ta' numri, a
lista marbuta ta 'numri, I bżonn tagħmel

892
00:41:52,560 --> 00:41:56,920
ftit aktar ħsieb bil-quddiem u
jiddikjara mhux biss int, imma Struct

893
00:41:56,920 --> 00:41:58,620
li jien ser sejħa, konvenzjonalment
hawn, node.

894
00:41:58,620 --> 00:42:01,630
Nistgħu sejħa hija xejn irridu, imma
node se jkunu tematiċi fil-lott

895
00:42:01,630 --> 00:42:03,560
mill-affarijiet aħna tibda tħares lejn issa.

896
00:42:03,560 --> 00:42:06,480
>> Ġewwa ta 'dik node huwa n int.

897
00:42:06,480 --> 00:42:09,350
U allura dan sintassi, ftit
stramb ewwel daqqa t'għajn -

898
00:42:09,350 --> 00:42:12,960
Struct node * jmiss.

899
00:42:12,960 --> 00:42:16,900
Ukoll pictorially, dak huwa li?

900
00:42:16,900 --> 00:42:21,000
Dan huwa l-nofs ta 'isfel ta'
-rettangolu li rajna

901
00:42:21,000 --> 00:42:22,730
ftit mument ilu.

902
00:42:22,730 --> 00:42:27,600
>> Imma għaliex jien qal Struct node *
għall-kuntrarju biss node *?

903
00:42:27,600 --> 00:42:31,370
Għaliex jekk dak pointer hija li tipponta
fil node ieħor, huwa biss il-

904
00:42:31,370 --> 00:42:32,760
indirizz ta 'node.

905
00:42:32,760 --> 00:42:35,630
C'est konsistenti ma 'dak li aħna ħadthom
diskuss dwar pointers s'issa.

906
00:42:35,630 --> 00:42:39,690
Iżda għaliex, jekk nitlob din l-istruttura hija
imsejħa node, għandi ngħid Struct

907
00:42:39,690 --> 00:42:42,660
node ġewwa hawn?

908
00:42:42,660 --> 00:42:43,190
>> Eżattament.

909
00:42:43,190 --> 00:42:46,490
Huwa tip ta 'realtà stupid ta' C.
Il typedef, biex ngħidu hekk, ma jkunx

910
00:42:46,490 --> 00:42:47,220
seħħx.

911
00:42:47,220 --> 00:42:48,510
C huwa super litterali.

912
00:42:48,510 --> 00:42:51,050
Jgħid kodiċi top tiegħek biex
qiegħ, xellug għal-lemin.

913
00:42:51,050 --> 00:42:54,930
U sakemm hits li semicolon fuq il-
bottom line, raden dak li ma

914
00:42:54,930 --> 00:42:57,590
jeżistu bħala tip ta 'data?

915
00:42:57,590 --> 00:42:59,060
Node, node unquote kwotazzjoni.

916
00:42:59,060 --> 00:43:03,050
>> Iżda minħabba l-aktar verbose
Dikjarazzjoni I ma fuq l-ewwel linja -

917
00:43:03,050 --> 00:43:05,340
typedef node Struct -

918
00:43:05,340 --> 00:43:08,790
minħabba li daħal l-ewwel, qabel il-
braces kaboċċi, li tip simili

919
00:43:08,790 --> 00:43:11,800
pre-edukazzjoni clang li, inti
taf liema, tagħti me a Struct

920
00:43:11,800 --> 00:43:13,570
imsejħa node Struct.

921
00:43:13,570 --> 00:43:16,270
Franchement, I ma simili li ssejjaħ affarijiet
Struct node, node Struct kollha

922
00:43:16,270 --> 00:43:17,090
matul kodiċi tiegħi.

923
00:43:17,090 --> 00:43:20,660
Imma jien ser jużawha biss darba, biss ġewwa,
I hekk li jista 'effettivament

924
00:43:20,660 --> 00:43:25,010
toħloq tip ta 'referenza ċirkolari, mhux
a pointer li myself per se, iżda

925
00:43:25,010 --> 00:43:29,400
pointer għall-ieħor ta '
tip identiċi.

926
00:43:29,400 --> 00:43:32,330
>> Għalhekk jirriżulta li fuq struttura tad-data
bħal dan, hemm ftit

927
00:43:32,330 --> 00:43:34,470
operazzjonijiet li jistgħu jkunu
ta 'interess lilna.

928
00:43:34,470 --> 00:43:37,460
Aħna tista 'tixtieq li daħħal
fi lista bħal din.

929
00:43:37,460 --> 00:43:39,850
Aħna tista 'tixtieq li jitħassar
minn lista bħal din.

930
00:43:39,850 --> 00:43:43,490
Aħna tista 'tixtieq li tfittex l-lista ta'
valur, jew b'mod iktar ġenerali, travers.

931
00:43:43,490 --> 00:43:46,410
U travers huwa biss mod fancy ta '
qal bidu fil-xellug u jimxu kollha

932
00:43:46,410 --> 00:43:47,650
il-mod lejn il-lemin.

933
00:43:47,650 --> 00:43:52,640
>> U avviż, anke ma 'dan ftit aktar
struttura tad-data sofistikati, let

934
00:43:52,640 --> 00:43:56,510
me tipproponi li nistgħu tissellef xi wħud
l-ideat tal-aħħar ġimgħatejn u

935
00:43:56,510 --> 00:43:58,410
timplimenta funzjoni msejħa
tfittxija bħal dan.

936
00:43:58,410 --> 00:44:01,360
Huwa ser jirritorna vera jew
falza, li jindika, iva jew

937
00:44:01,360 --> 00:44:03,390
ebda, n huwa fil-lista.

938
00:44:03,390 --> 00:44:05,960
Tieni argument tagħha huwa pointer
mal-lista nnifisha, sabiex a

939
00:44:05,960 --> 00:44:07,920
pointer għal node.

940
00:44:07,920 --> 00:44:10,350
>> All jien ser imbagħad tagħmel huwa jiddikjara
varjabbli temporanja.

941
00:44:10,350 --> 00:44:12,730
Aħna ser sejħa hija ptr b'konvenzjoni,
għall pointer.

942
00:44:12,730 --> 00:44:15,220
U jien tassenja ugwali għall-
bidu tal-lista.

943
00:44:15,220 --> 00:44:16,680
>> U issa avviż-loop waqt.

944
00:44:16,680 --> 00:44:20,640
Sakemm pointer mhux ugwali
li null, jien ser jiċċekkja.

945
00:44:20,640 --> 00:44:24,520
Huwa pointer n vleġġa ugwali għal
n li kienet għaddiet?

946
00:44:24,520 --> 00:44:26,410
U stenna minuta - ġdida
biċċa sintassi.

947
00:44:26,410 --> 00:44:29,324
X'inhu vleġġa kollha f'daqqa?

948
00:44:29,324 --> 00:44:30,574
Yeah?

949
00:44:30,574 --> 00:44:34,200

950
00:44:34,200 --> 00:44:34,810
>> Eżattament.

951
00:44:34,810 --> 00:44:38,860
Allura billi ftit minuti ilu, użajna
l-dot notazzjoni għall-aċċess xi ħaġa

952
00:44:38,860 --> 00:44:43,080
ġewwa ta 'l-Struct, jekk il-varjabbli
int mhux l-Struct

953
00:44:43,080 --> 00:44:47,420
innifsu, iżda pointer għal Struct,
Thankfully, biċċa sintassi li

954
00:44:47,420 --> 00:44:48,620
finalment jagħmel sens intuwittivi.

955
00:44:48,620 --> 00:44:52,360
Il-vleġġa jfisser li jsegwu l-pointer,
bħal vleġeġ tagħna tipikament ifisser

956
00:44:52,360 --> 00:44:56,570
pictorially, u jmorru fuq
data kulħadd kemm ġewwa.

957
00:44:56,570 --> 00:44:59,700
Allura vleġġa huwa l-istess ħaġa bħat dot, iżda
tużah meta jkollok pointer.

958
00:44:59,700 --> 00:45:05,270
>> Hekk biss biex terġa allura, jekk l-qasam n
ġewwa tal-Struct imsejħa pointer

959
00:45:05,270 --> 00:45:07,760
ugwali ugwali n, ritorn vera.

960
00:45:07,760 --> 00:45:11,970
Inkella, din il-linja hawn - pointer
ugwali pointer li jmiss.

961
00:45:11,970 --> 00:45:17,540
Allura dak li dan qed tagħmel, avviż, huwa jekk I
am bħalissa tipponta lejn il-Struct

962
00:45:17,540 --> 00:45:21,430
fihom 9, u 9 mhuwiex in-numru
I infittex - suppose I infittex

963
00:45:21,430 --> 00:45:22,830
għal n ugwali 50 -

964
00:45:22,830 --> 00:45:25,930
Jien ser taġġorna pointer temporanju tiegħi
li jurux f'dan node

965
00:45:25,930 --> 00:45:31,190
aktar, iżda pointer vleġġa li jmiss, li
se timplimenta me up here.

966
00:45:31,190 --> 00:45:34,270
>> Issa, I realizzati huwa whirlwind
introduzzjoni.

967
00:45:34,270 --> 00:45:37,380
Nhar l-Erbgħa, aħna ser fil-fatt jagħmlu dan
ma 'xi bnedmin u bi ftit aktar

968
00:45:37,380 --> 00:45:38,900
kodiċi b'pass kajman.

969
00:45:38,900 --> 00:45:42,990
Iżda realizzata, aħna qed issa qed data tagħna
strutturi aktar kumplessi sabiex tagħna

970
00:45:42,990 --> 00:45:45,780
algoritmi tista 'tikseb aktar effiċjenti, li
se tkun meħtieġa għall-

971
00:45:45,780 --> 00:45:50,500
pset sitt, meta aħna tagħbija, għal darb'oħra, dawk
150.000 kliem, iżda jeħtieġ li tagħmel hekk

972
00:45:50,500 --> 00:45:55,650
effiċjenti, u idealment, joħolqu
programm li tmur għall-utenti tagħna ma

973
00:45:55,650 --> 00:46:00,460
lineari, mhux f'N kwadrat, iżda
ħin kostanti, fil-ideal.

974
00:46:00,460 --> 00:46:02,300
>> Aħna ser tara inti nhar l-Erbgħa.

975
00:46:02,300 --> 00:46:07,240
>> SPEAKER: Fil-CS50 jmiss, David
jinsa każ bażi tiegħu.

976
00:46:07,240 --> 00:46:12,770
>> DAVID Malan: U li kif inti tibgħat
messaġġi bil C. X'inhu l -

977
00:46:12,770 --> 00:46:14,020
>> [MESSAĠĠ TEST VARJI
NOTIFIKA Ħsejjes]

978
00:46:14,020 --> 00:46:19,734