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[Powered by Google Translate] [WIKI 5]

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[David J. Malan, Chuo Kikuu cha Harvard]

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[Hii ni CS50.] [CS50.TV]

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[Mwanamke] Yeye amelala; kuhusu nini, mimi sijui.

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[Man] Basi nini sisi kujua?

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[Mwanamke] Hiyo saa 9:15, Ray Santoya ilikuwa kwa ATM.

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[Man] Hivyo swali ni, nini ilikuwa yeye kufanya saa 9:16?

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[Mwanamke] Risasi mm 9 katika kitu fulani.

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Labda aliona sniper.

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[Man] Au alikuwa anafanya kazi pamoja naye.

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[Mwanamke] Subiri. Nenda moja nyuma.

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[Man] Unaona nini?

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[♫ muziki Suspenseful ♫]

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[Mwanamke] Lete uso wake juu. Kamili screen.

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[Man] glasi wake. >> Kuna reflection.

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[♫ muziki Suspenseful ♫]

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[Man] Hiyo baseball Nuevita wa timu. Hiyo ni alama yao.

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[Mwanamke] Na yeye ni kuzungumza na mtu yeyote, s amevaa kwamba Jacket.

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>> [Daudi Malan] hiyo, hili ni CS50 wiki 5, na leo sisi uharibifu kidogo ya televisheni na sinema kwa ajili yenu.

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Hiyo wakati wowote wewe ni kuangalia show kama hii moja hapa,

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na Cops kusema "Je, wewe safi kuwa hadi?" au "Kuongeza,"

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hakuna kuongeza katika ulimwengu wa kweli.

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Kwa kweli, nini wewe kweli ni kupata kitu kidogo kama hii.

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Nimekuwa anapigiwa moja ya picha wafanyakazi kutoka ukurasa.

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Hii ni programu inayoitwa Photoshop. Hii ni 1 ya Bowdens 2,

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1 ya 3 Bowdens kweli, leo, kwa sababu tuna Bi Bowden hapa pia, na Rob na Paulo.

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Lakini hapa ni Rob kwenye screen, na kama sisi zoom katika juu ya glint kwamba yeye daima alikuwa katika jicho lake,

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nini hasa kuona kwamba ni nini kuona ni nini kupata.

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Hii ni "kuimarishwa," hivyo "CSI" kuwa ni kidogo makosa.

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Kuna mmoja video nyingine, kama tunaweza kuchukua juu ya "CSI" tu kidogo tena.

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Hii moja ni maneno nice atatoa sasa kama unataka

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sauti za kiufundi kwa rafiki yako wakati, kwa kweli, wewe ni kusema kitu kabisa.

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>> [Man] Kwa muda wa wiki Nimekuwa kuchunguza mauaji Killer Cabby

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na fascination fulani morbid.

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[Mama # 1] Hii ni katika muda halisi.

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[Mama # 2] Mimi utaunda interface GUI kutumia Visual Basic, kuona kama naweza kufuatilia anwani ya IP.

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>> [Malan] Basi audio nje ya Sync kando, kujenga interface GUI kutumia Visual Basic

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kufuatilia anwani ya IP ni kamili nonsense.

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Siku hizi bila kutumia Visual Basic,

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hakuna haja kwa GUI, na anwani ya IP alikuwa mrefu kitaalam sahihi.

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Hivyo kuweka jicho nje kwa ajili ya haya, na moja ya favorites yangu:

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Hii moja ni kidogo zaidi arcane, kwa sababu unahitaji kujua lugha tofauti.

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Kuna lugha inayoitwa Lengo-C, ambayo ni superset ya C.

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Ambayo ina maana ya C plus baadhi ya vipengele ziada, kati yao kitu-oriented programu.

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Na hii ni lugha ya kwamba Apple ina umaarufu kwa ajili ya programu iOS.

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Na hivyo hapa ni picha ya video kutoka show tofauti kabisa, kutoka "Hesabu,"

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kwamba kama kweli kuangalia kwa karibu juu ya TiVo yako na pause wakati wa kulia,

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utaona kwamba nini re kuangalia ni nini si kabisa kinachoelezwa.

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Na napenda kujaribu tofauti audio kontakt hapa na kuona kama hatuwezi

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kuweka audio katika Sync wakati huu.

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Mimi kukupa "Hesabu."

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>> [Man # 1] Ni ya 32-bit IPv4 anuani.

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[Man # 2] IP, hiyo ni ya internet. >> Private mtandao. Ni Anita binafsi ya mtandao.

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[Malan] Sawa. Hii ni Lengo-C, na ni kwa ajili ya kuchorea mpango baadhi mtoto wa,

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kama unaweza labda infer kutoka jina la kutofautiana huko.

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Hivyo hivyo, basi, ilikuwa "Hesabu." Hivyo leo na wiki hii sisi kuanzisha

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kidogo ya dunia ya forensics na muktadha katika matatizo kwa sababu hiyo.

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Leo itakuwa hotuba abbreviated kwa sababu kuna tukio maalum katika hapa

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baadaye, hivyo tutaweza kuchukua Peek, na tease wanafunzi wote na wazazi sawa leo

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na baadhi ya mambo ambayo ni juu ya upeo wa macho.

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Kati yao, kama ya Jumatatu, utakuwa chache wanafunzi zaidi.

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EdX, Harvard na mits mpya online mpango kwa wazi courseware

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na zaidi, ni uzinduzi juu ya chuo cha Harvard juu ya Jumatatu.

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Ambayo ina maana ya kuja Jumatatu utakuwa - kama ya kuhesabu mwisho,

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86,000 classmates ziada itakuwa kufuatia pamoja na mihadhara CS50 ya

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na sehemu na walkthroughs na seti tatizo.

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Na kama sehemu ya hii, utakuwa kuwa wanachama wa darasa uzinduzi wa

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CS50 na sasa CS50x.

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>> Kama sehemu ya hili, sasa, kutambua kwamba kutakuwa na baadhi upsides pia.

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Ili kupata tayari kwa ajili ya hii, kwa idadi kubwa ya wanafunzi,

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inatosha kusema kwamba hata kama tuna TFS 108 na CAS,

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si bora kabisa mwanafunzi / mwalimu uwiano mara moja sisi hit 80,000 wanafunzi wengine.

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Hivyo sisi siyo kwenda kuwa grading wengi tatizo seti manually.

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Hivyo ilianzisha wiki hii katika kuweka tatizo itakuwa CS50 Check,

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ambayo ni kwenda kuwa mstari amri shirika ndani ya appliance

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kwamba utapata mara moja update baadaye mwishoni mwa wiki hii,

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na wewe utakuwa na uwezo wa kukimbia amri, angalia 50,

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juu ya pset yako mwenyewe, na utapata baadhi ya maoni ya kama mpango wako ni

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sahihi au yasiyo sahihi kulingana na design mbalimbali specifikationer kwamba tuna zinazotolewa.

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Hivyo zaidi juu ya kuwa na vipimo tatizo kuweka na

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Classmates CS50x itakuwa kutumia hii kama vile.

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>> Hivyo tatizo kuweka 4 ni wote kuhusu forensics.

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Na kipande hii ulitokana na baadhi ya mambo halisi ya maisha,

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ambapo nilipokuwa katika shule ya kuhitimu, mimi interned kwa wakati na

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Ofisi Jina Middlesex ya Wilaya ya Mwanasheria kufanya kazi ya kuchunguza mauaji

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na mpelelezi wao risasi kuchunguza mauaji, na nini hii yalifikia

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ni, nadhani nilivyoeleza wiki iliyopita chache, ni Misa Jimbo polisi au watu wengine

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ingekuwa kuja katika, wangeweza kuacha mbali mambo kama anatoa ngumu na CD na disks floppy

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na kama, na kisha lengo la ofisi forensics ilikuwa ili kuhakikisha kama

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kulikuwa au hakuwa na ushahidi wa aina fulani.

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Hii ilikuwa Maalum Uchunguzi Unit, hivyo ilikuwa nyeupe-collar uhalifu,

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ilikuwa zaidi kumsumbua aina ya uhalifu,

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chochote kuwashirikisha baadhi ya aina ya vyombo vya habari digital; zinageuka kuwa si kwamba watu wengi

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kuandika barua pepe akisema "Mimi alifanya hivyo."

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Hivyo mara nyingi kabisa upekuzi forensics hawakufika matunda yote sana,

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lakini wakati mwingine watu bila kuandika barua pepe kama hizo.

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Hivyo wakati mwingine juhudi walipewa zawadi.

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>> Lakini kuwaongoza hadi pset hii ya kuchunguza mauaji, tutaweza kuwa kuanzisha katika pset 4 kidogo ya graphics.

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Hivyo pengine kuchukua mambo haya kwa nafasi, JPEGs GIFs, na kama siku hizi,

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lakini kama kweli kufikiri juu yake, sanamu, kiasi kama uso wa Rob,

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inaweza kuwa inatokana kama mlolongo wa dots, au Ukubwa.

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Sasa, katika kesi ya uso wa Rob, kuna kila aina ya rangi,

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na sisi kuanza kuona dots mtu binafsi, otherwide inayojulikana kama, saizi ya

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mara moja tulianza zoom in

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Lakini kama sisi kurahisisha dunia kidogo, na kusema tu kwamba hii hapa ni Rob

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katika nyeusi na nyeupe, vizuri, kuwakilisha nyeusi na nyeupe tunaweza tu kutumia binary.

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Na kama sisi ni kwenda kutumia binary, 1 au 0, tunaweza kueleza picha hii sawa

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ya uso wa Rob smiling na muundo huu wa bits: 11000011 inawakilisha

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nyeupe, nyeupe, nyeusi, nyeusi, nyeusi, nyeusi, nyeupe nyeupe.

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Na hivyo si leap kubwa, basi, kuanza kuzungumza juu ya picha colourful.

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Mambo ambayo unaweza kuiona kwenye Facebook au kuchukua na kamera ya digital,

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lakini, kwa hakika, linapokuja rangi, unahitaji bits zaidi.

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Na kawaida kabisa katika ulimwengu wa picha ni kutumia si 1-bit Michezo,

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kama hii unaonyesha, lakini 24-bit Michezo, ambapo kwa kweli kupata mamilioni ya rangi.

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Hivyo kama katika kesi wakati sisi zoomed katika juu ya jicho Rob wa,

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kwamba ilikuwa na idadi yoyote ya mamilioni ya uwezekano tofauti colorful.

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>> Hivyo tutaweza kuanzisha hii katika tatizo kuweka 4 kama vile katika walkthrough,

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ambayo itakuwa leo saa 3:30 badala ya 2:30 kawaida kwa sababu ya hotuba ya Ijumaa hapa.

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Lakini video itakuwa online, kama kawaida, kesho.

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Tutaweza pia kuanzisha wewe format faili nyingine.

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Hivyo hii ni makusudi maana ya kuangalia vitisho mara ya kwanza,

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lakini hii ni baadhi tu nyaraka kwa ajili ya struct C.

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Ni zinageuka kuwa Microsoft, miaka iliyopita, umesaidia wanatangaza hii format,

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kuitwa bitmap faili format, BMP, na hii ilikuwa super-rahisi,

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colourful graphical faili format ambayo ilitumika kwa muda kabisa

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na wakati mwingine bado kwa wallpapers kwenye kopyuta.

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Kama unafikiri nyuma kwa Windows XP na milima rolling na anga ya bluu,

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kwamba ilikuwa kawaida BMP, au picha bitmap, na bitmaps

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ni furaha kwa ajili yetu kwa sababu wana kidogo zaidi utata.

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Ni kabisa kama rahisi kama hii ya gridi ya 0 na 1 ya;

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badala yake, una vitu kama header mwanzoni ya faili.

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Hivyo kwa maneno mengine, ndani ya faili bmp. Ni rundo zima la wa 0 na 1 ya,

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lakini kuna baadhi ya ziada 0 na 1 ya huko.

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Na zinageuka kuwa kile ambacho tumekuwa pengine kuchukuliwa kwa nafasi kwa miaka,

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file format kama. doc xls au. au. mp3 au. mp4,

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chochote format faili kwamba wewe ni ukoo na.

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Naam, ni nini hata maana ya kuwa format faili?

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Kwa sababu mwisho wa siku, wote wa files haya sisi kutumia kuwa tu 0 na 1 ya

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na labda wale 0 na 1 ya kuwakilisha, b, c, kupitia ASCII au kama,

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lakini kwa njia ya mwisho wa siku, ni tu 0 na 1 ya.

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>> Hivyo binadamu tu mara kwa mara ya kuamua mzulia faili mpya format

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ambapo wao standardize nini mwelekeo wa bits kwa kweli maana.

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Na katika kesi hii hapa, folks ambao iliyoundwa bitmap faili format

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alisema kuwa katika Byte sana kwanza katika faili bitmap, kama ulionyehsa kwa kukabiliana 0, kuna,

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kuna kwenda kuwa baadhi isiyoeleweka kirahisi aitwaye variable kuitwa bfType,

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ambayo tu anasimama kwa ajili ya aina bitmap faili; ni aina gani ya faili bitmap hii ni.

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Unaweza infer, pengine, kutoka safu ya pili kwamba kukabiliana 2, Byte idadi 2,

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ina mfano wa Mungu na 0 1 kwamba inawakilisha nini?

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ukubwa wa kitu fulani, na unaendelea kutoka huko.

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Hivyo katika tatizo kuweka 4, wewe utakuwa kutembea kwa njia ya baadhi ya mambo haya.

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>> Sisi si kuishia kujali juu ya wote, lakini taarifa ni kuanza kupata kuvutia

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kuzunguka mstari au Byte 54, rgbtBlue, Green na Red.

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Kama ve milele habari kifupi RGB, nyekundu kijani bluu, hii ni kumbukumbu ya kwamba.

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Kwa sababu ni zamu nje unaweza rangi rangi zote za upinde wa mvua

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na baadhi ya macho ya nyekundu na bluu na kijani.

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Na, kwa kweli, wazazi katika chumba wapate kukumbuka baadhi ya madomo mwanzo.

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Siku hizi, wewe tu kuona 1 mwanga mkali kuja nje ya Lens.

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Lakini nyuma katika siku, wewe alikuwa Lens nyekundu, Lens bluu, na Lens kijani

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na pamoja nao kwa lengo la screen na sumu picha colourful.

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Na mara nyingi kabisa katikati ya shule na shule za sekondari ingekuwa lenses wale

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milele-ili-kidogo potovu, hivyo walikuwa aina ya kuona picha mara mbili au tatu,

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lakini kwamba alikuwa na wazo. You alikuwa nyekundu na kijani na bluu mwanga uchoraji picha.

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Na kanuni hiyo ni kutumika katika kompyuta.

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>> Hivyo kati ya changamoto, basi, kwa ajili yenu katika tatizo kuweka 4

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itakuwa ni ya mambo kadhaa, moja ni kweli resize picha.

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Kuchukua katika muundo wa wa 0 na 1 ya,

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kufikiri ambayo chunks ya ya 0 na 1 ya kuwakilisha nini katika muundo kama hii,

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na kisha kufikiri ni jinsi gani ya kuiga saizi: boundin, blues, wiki

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ndani ili wakati picha inaonekana kama hii ya awali, ili kuangalia kama hii badala baada ya hapo.

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Miongoni mwa changamoto nyingine, pia, ni kwenda kuwa kuwa wewe utakuwa mitupu

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picha ya kuchunguza mauaji ya faili halisi kutoka kamera ya digital

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na juu ya kamera kwamba, mara moja juu ya muda, walikuwa rundo zima la photos.

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Tatizo ni, sisi ajali erased au alikuwa image kupotoshwa kwa namna fulani.

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Mambo mabaya kutokea kwa kamera ya digital, na hivyo sisi haraka kunakiliwa yote ya ya 0 na 1 ya

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mbali ya kwamba kadi kwa ajili yenu, kuokolewa kwao wote katika faili 1 kubwa, na kisha tutaweza mkono wao kwa wewe

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katika tatizo kuweka 4 ili uweze kuandika mpango katika C na ambayo kupona

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wote wa JPEGs hizo, walau.

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Na zinageuka JPEGs kwamba, ingawa wao ni kiasi fulani ya muundo tata ya SVG,

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wao uko magumu zaidi kuliko uso hii smiling hapa.

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Ni zinageuka kuwa kila JPEG kuanza na mwelekeo huo wa wa 0 na 1 ya.

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Hivyo kwa kutumia kitanzi wakati au kwa kitanzi au sawa,

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unaweza iterate juu ya wote 0 na 1 katika picha hii ya kuchunguza mauaji

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na kila wakati unaweza kuona mfano maalum ambacho defined katika vipimo kuweka tatizo la,

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unaweza kudhani, 'Oh, hapa ni pamoja na uwezekano juu sana,

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mwanzo wa JPEG, 'na kwa haraka kama wewe kupata mfano huo,

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baadhi idadi ya ka au kilobytes au megabaiti baadaye,

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unaweza kudhani, 'Ooh! Hapa ni JPEG pili, picha mimi alichukua baada ya moja ya kwanza.

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Hebu kuacha kusoma kwamba faili kwanza, kuanza kuandika hii moja mpya. '

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Na pato la mpango wako kwa pset 4 ni kwenda kuwa kama wengi kama 50 JPEGs.

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Na kama siyo 50 JPEGs, una kidogo ya kitanzi.

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Kama una idadi ya usio wa JPEGs, una kitanzi usio.

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Hivyo kwamba, pia, itakuwa kesi ya kawaida kabisa.

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Hiyo ni nini juu ya upeo wa macho.

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>> Maswali 0, nyuma yetu. Kutambua, kwa email yangu, kwamba invariably kuna folks

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wote ambao ni furaha, ni aina ya neutral, na kusikitisha kuzunguka Jaribio 0 muda.

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Na tafadhali kufikia nje kwangu, TFS kichwa, Zamyla, TF yako mwenyewe

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au moja ya CAS kwa kuwa wewe kujua kama ungependa kujadili jinsi mambo akaenda.

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>> Hivyo kumvutia wazazi hapa katika chumba,

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kile ni maktaba CS50? Kazi nzuri.

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Nini maktaba CS50? Yeah? [Mwanafunzi majibu, unintelligible]

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>> Okay, nzuri. Hivyo ni kuweka prewritten ya kificho kwamba sisi, wafanyakazi, aliandika,

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sisi kutoa na wewe, kwa kutoa functionalities baadhi ya kawaida.

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Stuff like kupata yangu string; kupata yangu int, wote wa kazi ambayo yameorodheshwa hapa.

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Kuanzia sasa, sisi kuanza kwa kweli kuchukua magurudumu haya mafunzo mbali.

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Hivyo sisi ni kwenda kuanza kuchukua "kamba" kutoka kwenu,

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ambayo, wanakumbuka, mara tu kisawe kwa ajili ya aina yale halisi data? Char *.

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Hivyo kwa wazazi, kwamba labda - kwamba ni nzuri, hivyo * Char tutaweza kuanza kuona

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juu ya screen wote zaidi kama sisi kuondoa "kamba" kutoka msamiati wetu,

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angalau linapokuja kweli kuandika code.

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Vile vile, tutaweza kuacha kutumia baadhi ya kazi hizi kama mengi,

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kwa sababu mipango yetu ni kwenda kupata kisasa zaidi

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badala tu ya kuandika mipango kwamba kukaa pale na blinking haraka,

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kusubiri kwa mtumiaji na aina kitu in

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Utapata pembejeo yako kutoka mahali pengine.

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Kwa mfano, utapata yao kutoka katika mfululizo wa bits kwenye gari mitaa ngumu.

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Wewe utakuwa badala kupata yao katika siku zijazo kutoka uhusiano wa mtandao, baadhi tovuti mahali fulani.

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Basi hebu peel safu nyuma hii kwa mara ya kwanza, na kuvuta up appliance CS50

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na faili hii inaitwa CS50.h, ambayo wewe tumekuwa mkali ikiwa ni pamoja na kwa wiki.

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>> Lakini hebu kweli kuona nini ndani ya hii.

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Hivyo juu ya faili katika bluu ni tu rundo zima la maoni,

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udhamini habari na leseni. Hii ni aina ya dhana ya kawaida

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katika programu, kwa sababu mengi ya programu siku hizi ni nini inayoitwa "chanzo wazi,"

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ambayo ina maana kwamba mtu ameandika code

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na alifanya hivyo kwa uhuru zaidi, si tu kukimbia na kutumia,

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lakini kwa kweli kusoma na kubadilisha na kuunganisha katika kazi yako mwenyewe.

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Hivyo kwamba ni nini tumekuwa kutumia, wazi chanzo programu,

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angalau katika fomu ndogo sana.

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Kama mimi kitabu chini cha maoni, ingawa, tutaweza kuanza kuona baadhi ya mambo zaidi ya ukoo.

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Hivyo taarifa juu hapa, kwamba faili CS50.h ni pamoja na rundo zima la files header.

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Sasa, wengi wa hawa hatujaona kabla, lakini moja ni

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zinazojulikana, ambayo ya hizi sisi kuonekana, angalau kwa ufupi, hivi sasa?

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Yeah, kiwango maktaba. Stdlib.h ina malloc,

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hivyo mara moja tulipoanza kuzungumza kuhusu mgao nguvu kumbukumbu,

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ambayo tutaweza kurudi wiki ijayo kama vizuri, sisi ilianza ikiwa ni pamoja na faili hilo.

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Ni zinageuka kuwa bool na kweli na uongo si kweli zipo katika C, per se,

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isipokuwa wewe ni pamoja na faili hii hapa.

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Hivyo tuna, kwa wiki, ikiwa ni pamoja na kiwango wamekuwa bool.h

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hivyo kwamba unaweza kutumia dhana ya bool, kweli au uongo.

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Bila hili, ungependa kuwa na aina ya bandia na kutumia int

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na tu kiholela kudhani kwamba 0 ni uongo na 1 ni kweli.

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>> Sasa, kama sisi kitabu chini zaidi, hapa ni ufafanuzi yetu ya kamba.

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Ni zinageuka, kama tumekuwa alisema kabla, kwamba ambapo * hii ni kweli haina jambo.

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Unaweza hata kuwa na nafasi pande zote.

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Sisi, hii muhula, wamekuwa kukuza kama hii kufanya wazi kwamba * ina nini na aina.

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Lakini kutambua, kama kawaida, kama siyo kidogo zaidi ya kawaida, ni kuweka huko

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lakini functionally ni kitu kimoja.

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Lakini sasa, kama sisi kusoma chini zaidi, hebu kuchukua kuangalia kusema, GetInt,

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kwa sababu sisi kutumika kwamba, pengine, kabla ya kitu kingine chochote hii muhula.

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Na hapa ni GetInt. Hii ni nini?

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Hii ni mfano. Hivyo mara nyingi, tuna kuweka prototypes katika vilele vya wetu c files.,

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lakini unaweza pia kuweka prototypes katika files header,. files h,

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kama hii moja hapa, hivyo kwamba wakati wewe kuandika baadhi ya majukumu

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kwamba unataka watu wengine kuwa na uwezo wa kutumia, ambayo ni hasa kesi na maktaba CS50,

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wewe si tu kutekeleza majukumu yako katika kitu kama CS50.c,

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wewe pia kuweka prototypes si wakati juu ya faili kwamba, lakini wakati juu ya faili header,

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basi kwamba faili header ni nini marafiki na wafanyakazi wenzake ni pamoja na,

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na mkali pamoja katika kanuni zao wenyewe.

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Hivyo muda wote huu tumekuwa pamoja wote prototypes hizi

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ufanisi katika juu ya faili yako, lakini kwa njia ya hii ni pamoja na utaratibu mkali

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kwamba kimsingi nakala na pastes faili hii katika yako mwenyewe.

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Sasa, hapa ni baadhi ya nyaraka uungwana kina.

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>> Tumekuwa pretty much kuchukuliwa kwa nafasi ya kuwa GetInt anapata int,

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lakini zinageuka kuna kesi kona baadhi, haki?

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Nini kama mtumiaji aina katika idadi hiyo ni njia kubwa mno?

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quintillion, kwamba tu hawezi fit ndani ya int?

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Je, ni tabia yanayotarajiwa? Naam, walau, ni kutabirika.

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Hivyo katika kesi hii, kama kweli kusoma magazeti faini,

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utaona kwamba kama mstari hauwezi kusoma, hii INT_MAX atakaporudi.

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Sisi sijawahi kuongelea kuhusu hili, lakini kwa kuzingatia mtaji wake,

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ni nini, pengine?

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Ni mara kwa mara, hivyo ni baadhi ya mara kwa mara maalum kwamba pengine alitangaza

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katika moja ya files wale header kwamba ni juu ya juu katika faili,

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na INT_MAX pengine ni kitu kama, ukali, bilioni 2.

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wazo kuwa kuwa sababu tunahitaji namna fulani yanamaanisha kwamba kitu potoka,

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sisi, ndiyo, na idadi bilioni 4 katika ovyo yetu,

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hasi juu ya bilioni 2 hadi bilioni 2, kutoa au kuchukua.

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Naam, ni ya kawaida katika programu hii ni wewe kuiba moja tu ya wale idadi.

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Labda 0, labda bilioni 2, labda hasi bilioni 2.

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Hivyo wewe kutumia moja ya maadili yako iwezekanavyo ili uweze kufanya kwa dunia

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kwamba kama kitu fulani kitaenda vibaya, nitarudi thamani hii super-kubwa.

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Lakini hutaki mtumiaji kuandika kitu cryptic kama "2, 3, 4 ..."

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ya idadi kubwa kweli kweli, ambapo badala generalize kama mara kwa mara.

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Hivyo kweli, kama wewe walikuwa kuwa anal majuma machache yaliyopita,

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wakati wowote wewe piga GetInt, unapaswa kuwa na hali ya kuangalia kama.

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Je aina user katika INT_MAX, au zaidi hasa,

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alifanya GetInt kurudi INT_MAX? Kwa sababu kama ni hivyo,

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kwamba kwa kweli ina maana hawakuwa unapoandika; kitu potoka katika kesi hii.

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Hivyo hii ni nini ujumla inayojulikana kama thamani "sentinel", ambayo ina maana maalum.

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>> Naam, hebu sasa kurejea katika c. Files.

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Faili C limekuwepo katika appliance kwa muda fulani,

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na, kwa kweli, appliance ina precompiled kwa wewe

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ndani ya jambo kwamba sisi kuitwa "kitu kificho,"

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lakini ni tu Haijalishi wewe ambapo ni kwa sababu mfumo anajua,

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katika kesi hii, ambako ni, appliance.

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Lakini hebu kitabu chini sasa kwa GetInt, na kuona jinsi GetInt imekuwa ikifanya kazi muda wote huu.

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Hivyo hapa tuna sawa maoni kutoka kabla.

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Hebu kuvuta tu sehemu ya kificho,

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na kile sisi kwa GetInt ni zifuatazo.

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Inachukua hakuna pembejeo na kuirudisha int, wakati (wa kweli), hivyo tuna makusudi usio kitanzi

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lakini, labda, tutaweza kuvunja nje ya hii kwa namna fulani, au kurudi kutoka ndani ya hii.

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Basi hebu angalia jinsi hii matendo. Naam, sisi wanaonekana kuwa na kutumia GetString

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katika mstari huu wa kwanza ndani ya kitanzi, 166.

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Hii sasa ni mazoezi mazuri kwa sababu chini ya mazingira gani

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inaweza GetString kurudi hii maalum Keyword, null?

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Kama kitu fulani kitaenda vibaya. Je, inaweza kwenda vibaya wakati wewe piga kitu kama GetString?

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Yeah? [Mwanafunzi jibu, unintelligible] >> Yeah. Hivyo labda malloc inashindwa.

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Mahali fulani chini GetString Hood wito malloc,

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ambao unagawa kumbukumbu, ambayo inakuwezesha kuhifadhi kompyuta

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yote ya wahusika kwamba mtumiaji aina katika keyboard.

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Na kudhani mtumiaji alikuwa na mengi nzima ya muda bure

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na typed zaidi, kwa mfano, zaidi ya herufi bilioni 2.

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Zaidi ya wahusika kuliko kompyuta hata ina RAM.

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Naam, GetString ina kuwa na uwezo kwa ishara ya kwamba na wewe,

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hata kama hii ni super, super kawaida kona kesi.

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Ina kwa namna fulani kuwa na uwezo wa kushughulikia suala hili, na hivyo GetString,

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kama sisi kurudi nyuma na kusoma nyaraka zake, haina, kwa kweli, kurudi null.

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Sasa kama GetString inashindwa na kurudi null, GetInt ataenda kushindwa

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na kurudi INT_MAX, kama sentinel.

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Hizi ni baadhi tu ya binadamu makongamano. njia pekee ya kujua hii ni kesi

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ni kwa kusoma nyaraka.

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Basi hebu kitabu chini ambapo int ni kweli GotInt.

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>> Hivyo kama mimi kitabu chini kidogo zaidi, katika mstari 170 tuna maoni juu ya mistari haya.

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Hivyo sisi kutangaza, katika 172, n int na c Char, na kisha kazi hii mpya

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ambayo baadhi yenu mashaka hela kabla, lakini sscanf.

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Hii anasimama kwa kamba f Scan.

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Kwa maneno mengine, nipe string nami Scan kwa vipande vya habari ya riba.

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Hiyo ni nini maana ya kwamba? Naam, tuseme kwamba ninapoandika katika, literally, 1 2 3 katika keyboard,

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na kisha hit kuingia. Je, ni aina ya data 1 2 3 wakati akarudi na GetString?

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Ni wazi kamba, sawa? I got kamba, hivyo 1 2 3 ni kweli "1 2 3"

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na 0 \ katika mwisho wake. Hiyo siyo int.

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Hiyo si idadi. Inaonekana kama idadi lakini si kweli.

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Hiyo ni nini GetInt kufanya? Ina Scan kwamba string kushoto na kulia,

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1 2 3 \ 0, na kwa namna fulani kubadilisha kwa integer halisi.

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Sasa, unaweza kufikiri ni jinsi gani ya kufanya hivyo.

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Kama unafikiri nyuma pset 2, wewe labda got kidogo starehe

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kwa Kaisari, au vigenere hivyo unaweza iterate juu ya kamba,

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unaweza kubadilisha chars kwa ints na pick. Hiyo ni mengi yote ya kazi.

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Mbona si wito kazi kama sscanf kwamba gani kwa ajili yenu?

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Hivyo sscanf anatarajia hoja, katika kesi hii inaitwa mstari, ambayo ni kamba.

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Wewe basi bayana, katika quotes, ni sawa na printf,

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je, wewe kutarajia kuona katika kamba hii?

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Nini mimi kusema hapa ni, mimi kutarajia kuona idadi decimal na labda tabia.

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Na tutaweza kuona nini hii ni kesi katika muda tu.

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Ni zinageuka kuwa nukuu hii sasa ni kukumbusha ya mambo

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tulipoanza kuzungumza kuhusu tu zaidi ya wiki iliyopita.

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>> Nini ni & n na & c kufanya kwa sisi hapa? [Mwanafunzi majibu, unintelligible]

347
00:21:05,430 --> 00:21:07,610
>> Yeah. Ni kunipa anuani ya n na anuani ya c.

348
00:21:07,610 --> 00:21:10,440
Sasa, kwa nini ni muhimu kwamba? Naam, unajua kwamba pamoja na utendaji katika C

349
00:21:10,440 --> 00:21:13,440
unaweza daima kurudi thamani au hakuna thamani wakati wote.

350
00:21:13,440 --> 00:21:16,630
Unaweza kurudi int, kamba, kuelea, char, chochote.

351
00:21:16,630 --> 00:21:21,150
Au unaweza kurudi batili, lakini unaweza tu kurudi 1 kitu Upeo.

352
00:21:21,150 --> 00:21:26,100
Lakini hapa tunataka sscanf kurudi kwangu labda int, idadi decimal,

353
00:21:26,100 --> 00:21:29,240
na pia Char, na mimi itabidi kueleza kwa nini Char katika wakati huu.

354
00:21:29,240 --> 00:21:34,250
Hivyo ufanisi wanataka f kurudi mambo 2; kwamba si tu inawezekana katika C.

355
00:21:34,250 --> 00:21:38,460
Hivyo unaweza kufanya kazi ya kuzunguka kwamba kwa kupita katika anwani 2,

356
00:21:38,460 --> 00:21:43,710
kwa sababu kwa haraka kama wewe mkono kazi anwani 2, nini wanaweza kufanya kazi hiyo pamoja nao?

357
00:21:43,710 --> 00:21:49,880
Ni unaweza kuandika kwa anwani hizo. Unaweza kutumia operesheni * na "kwenda huko" kwa kila moja ya anwani hizo.

358
00:21:49,880 --> 00:21:54,320
Ni aina ya mfumo huu backdoor, lakini kawaida sana kwa ajili ya kubadilisha maadili ya vigezo

359
00:21:54,320 --> 00:21:58,020
katika zaidi ya 1 tu mahali, katika kesi hii 2.

360
00:21:58,020 --> 00:22:04,590
Sasa, mimi nina taarifa ya kuangalia kwa == to1, na kisha kurudi n kama hana, kwa kweli, kutathmini kwa kweli.

361
00:22:04,590 --> 00:22:09,340
Basi nini kinaendelea? Naam, kitaalam, wote kweli tunataka kutokea katika GetInt ni hii.

362
00:22:09,340 --> 00:22:12,340
Tunataka kuchanganua, hivyo kusema; tunataka kusoma string

363
00:22:12,340 --> 00:22:16,210
"1 2 3" na kama inaonekana kama kuna idadi huko,

364
00:22:16,210 --> 00:22:21,360
nini tuko kuwaambia sscanf kufanya ni kuweka kwamba idadi, 1 2 3, katika n hii variable kwa ajili yangu.

365
00:22:21,360 --> 00:22:26,060
Kwa nini, basi, alifanya nina hili pia?

366
00:22:26,060 --> 00:22:33,750
Je, jukumu la pia akisema, sscanf, unaweza pia kupata tabia hapa.

367
00:22:33,750 --> 00:22:36,890
[Mwanafunzi akizungumza, unintelligible] >> Si - uhakika decimal anaweza kufanya kazi.

368
00:22:36,890 --> 00:22:40,650
Hebu kushikilia kwamba walidhani kwa muda. Gani kingine?

369
00:22:40,650 --> 00:22:42,570
[Mwanafunzi, unintelligible] >> Hivyo, wazo nzuri, inaweza kuwa tabia null.

370
00:22:42,570 --> 00:22:44,970
Ni kweli si, katika kesi hii. Yeah? [Mwanafunzi, unintelligible]

371
00:22:44,970 --> 00:22:47,100
>> >> ASCII. Au, basi mimi generalize hata zaidi.

372
00:22:47,100 --> 00:22:49,670
C% kuna tu kwa makosa ya kuangalia.

373
00:22:49,670 --> 00:22:52,510
Hatutaki kuwa kuna tabia baada ya idadi,

374
00:22:52,510 --> 00:22:54,980
lakini nini hii inaruhusu mimi kufanya ni yafuatayo:

375
00:22:54,980 --> 00:23:01,270
Ni zinageuka kuwa sscanf, badala ya kuhifadhi maadili katika n na c, katika mfano huu hapa,

376
00:23:01,270 --> 00:23:08,170
nini pia haina ni kuirudisha idadi ya vigezo ni kuweka maadili in

377
00:23:08,170 --> 00:23:13,330
Hivyo kama wewe tu aina katika 1 2 3, basi tu d% ni kwenda kwa mechi

378
00:23:13,330 --> 00:23:18,830
na tu n anapata kuhifadhiwa kwa thamani kama 1 2 3 na kitu anapata kuweka katika c;

379
00:23:18,830 --> 00:23:20,870
c bado thamani ya takataka, hivyo kusema.

380
00:23:20,870 --> 00:23:23,550
Takataka kwa sababu ni haijawahi initialized kama thamani fulani.

381
00:23:23,550 --> 00:23:29,390
Hivyo katika kesi hiyo, sscanf anarudi 1, kwa sababu mimi wakazi moja ya kuyatumia hizo,

382
00:23:29,390 --> 00:23:33,650
katika kesi ambayo, kubwa. Nina int, hivyo mimi huru line ya bure juu ya kumbukumbu

383
00:23:33,650 --> 00:23:37,150
kwamba GetString kweli zilizotengwa, na kisha mimi kurudi n.

384
00:23:37,150 --> 00:23:42,210
Mwingine, kama umewahi kujiuliza ambapo kwamba retry kauli huja kutoka, linatokana na haki hapa.

385
00:23:42,210 --> 00:23:45,770
Kama, kwa kulinganisha, ninapoandika katika 1 2 3 foo,

386
00:23:45,770 --> 00:23:48,640
baadhi tu mlolongo random wa maandishi, sscanf ni kwenda kuona,

387
00:23:48,640 --> 00:23:51,500
ooh, idadi, ooh, idadi, ooh, idadi, ooh - f.

388
00:23:51,500 --> 00:23:54,190
Na ni kwenda kuweka 1 2 3 katika n.

389
00:23:54,190 --> 00:23:59,970
Ni kwenda kuweka f katika c, na kisha kurudi 2.

390
00:23:59,970 --> 00:24:02,980
Hivyo tuna, tu kutumia ufafanuzi wa msingi wa tabia ya scanf,

391
00:24:02,980 --> 00:24:06,170
njia rahisi sana - vizuri, tata katika mtazamo wa kwanza, lakini mwisho wa siku,

392
00:24:06,170 --> 00:24:11,460
haki rahisi utaratibu wa kusema, ni pale int, na kama ni hivyo, ni kwamba kitu pekee mimi kupatikana?

393
00:24:11,460 --> 00:24:14,950
Na nafasi nyeupe hapa ni makusudi. Kama unaweza kusoma nyaraka kwa ajili ya sscanf,

394
00:24:14,950 --> 00:24:18,690
ni anakwambia kwamba kama wewe ni pamoja na kipande ya nafasi nyeupe mwanzoni au mwishoni,

395
00:24:18,690 --> 00:24:24,990
sscanf pia itaruhusu mtumiaji, kwa sababu yoyote, hit spacebar 1 2 3, na hiyo itakuwa halali.

396
00:24:24,990 --> 00:24:28,310
Itakuwa si yell katika user tu kwa sababu wao hit spacebar mwanzoni au mwishoni,

397
00:24:28,310 --> 00:24:32,160
ambayo ni kidogo tu zaidi user-kirafiki.

398
00:24:32,160 --> 00:24:34,160
>> Maswali yoyote, basi, juu ya GetInts? Yeah?

399
00:24:34,160 --> 00:24:36,820
[Mwanafunzi swali, unintelligible]

400
00:24:36,820 --> 00:24:40,740
>> Bora swali. Je, iwapo tu typed katika Char, kama hit f, na kuingia

401
00:24:40,740 --> 00:24:47,830
bila hata kuandika 1 2 3; unafikiri nini tabia ya huu mstari wa kanuni basi ingekuwa?

402
00:24:47,830 --> 00:24:50,500
Hivyo sscanf unaweza cover kwamba pia, kwa sababu katika kesi hiyo,

403
00:24:50,500 --> 00:24:56,280
si kwenda kujaza n au c; itakavyo badala kurudi 0.

404
00:24:56,280 --> 00:25:01,540
Katika kesi ambayo, mimi nina pia kuambukizwa kwamba hali hiyo, kwa sababu thamani inatarajiwa nataka ni 1.

405
00:25:01,540 --> 00:25:07,310
Mimi nataka tu 1, na kitu pekee 1 ya kujazwa. Nzuri swali. Wengine?

406
00:25:07,310 --> 00:25:09,610
>> Haki ya wote, hivyo basi si kwenda kwa yote ya kazi katika hapa,

407
00:25:09,610 --> 00:25:11,820
lakini moja ambayo inaonekana kuwa, pengine, riba iliyobaki

408
00:25:11,820 --> 00:25:14,530
ni kwa sababu GetString zinageuka kuwa GetFloat, GetInt,

409
00:25:14,530 --> 00:25:19,490
GetDouble, GetLongLong wote punt mengi ya utendaji wao wa GetString.

410
00:25:19,490 --> 00:25:22,860
Basi hebu tuangalie jinsi yeye ni kutekelezwa hapa.

411
00:25:22,860 --> 00:25:27,040
Hii moja inaonekana tata kidogo lakini inatumia misingi hiyo

412
00:25:27,040 --> 00:25:29,680
kwamba sisi kuanza kuzungumza kuhusu wiki iliyopita. Hivyo katika GetString,

413
00:25:29,680 --> 00:25:32,670
ambayo inachukua hakuna hoja kama kwa utupu hapa juu,

414
00:25:32,670 --> 00:25:37,110
na kuirudisha string; hivyo mimi kutangaza string kuitwa buffer.

415
00:25:37,110 --> 00:25:39,670
Mimi kwa kweli sijui ni nini ambayo inaenda kutumika kwa ajili bado, lakini tutaweza kuona.

416
00:25:39,670 --> 00:25:42,950
Looks kama uwezo ni, kwa default, 0; uhakika kabisa ambapo hii ni kwenda.

417
00:25:42,950 --> 00:25:44,920
Uhakika nini n kinaendelea kutumiwa kwa maana bado.

418
00:25:44,920 --> 00:25:47,860
Lakini sasa ni kupata zaidi kidogo ya kuvutia, hivyo katika mstari 243,

419
00:25:47,860 --> 00:25:51,760
sisi kutangaza c int, hii ni aina ya kina ya kijinga.

420
00:25:51,760 --> 00:25:58,080
Char ni 8 bits, na 8 bits unaweza kuhifadhi wangapi maadili tofauti?

421
00:25:58,080 --> 00:26:03,310
256. Tatizo ni, kama unataka kuwa na 256 tofauti wahusika ASCII,

422
00:26:03,310 --> 00:26:06,210
ambayo kuna, kama unafikiri nyuma, na hii si kitu kwa kukariri.

423
00:26:06,210 --> 00:26:09,100
Lakini kama unadhani nyuma chati kwamba kubwa ASCII tulikuwa wiki iliyopita,

424
00:26:09,100 --> 00:26:13,780
walikuwepo, katika kesi hiyo, 128 au 256 ASCII wahusika.

425
00:26:13,780 --> 00:26:16,220
Sisi kutumika mifumo yote ya ya 0 na 1 ya juu.

426
00:26:16,220 --> 00:26:19,410
Hiyo ni tatizo kama unataka kuwa na uwezo wa kuchunguza makosa.

427
00:26:19,410 --> 00:26:23,290
Kwa sababu kama uko tayari kutumia maadili 256 kwa wahusika wako,

428
00:26:23,290 --> 00:26:26,390
wewe si kweli mpango wa mbele, kwa sababu sasa una hakuna njia ya kusema,

429
00:26:26,390 --> 00:26:29,750
"Hii si tabia legit, hii ni kwa baadhi ya ujumbe makosa."

430
00:26:29,750 --> 00:26:32,430
Basi nini dunia gani ni, wao kutumia ijayo kubwa thamani,

431
00:26:32,430 --> 00:26:35,790
kitu kama int ili una idadi mambo ya bits,

432
00:26:35,790 --> 00:26:39,610
32 kwa maadili bilioni 4 iwezekanavyo, ili kwamba unaweza tu kuishia kutumia,

433
00:26:39,610 --> 00:26:44,800
kimsingi, 257 kati yao, 1 ambayo ina baadhi ya maana maalum kama makosa.

434
00:26:44,800 --> 00:26:49,190
>> Basi hebu angalia jinsi hii matendo. Katika mstari 246, nina hii kubwa wakati kitanzi

435
00:26:49,190 --> 00:26:54,530
kwamba ni wito fgetc, f maana ya SVG, getc, na kisha stdin.

436
00:26:54,530 --> 00:26:59,030
Zinageuka hii ni njia tu sahihi zaidi ya kusema "kusoma pembejeo kutoka keyboard."

437
00:26:59,030 --> 00:27:02,730
Darasa la pembejeo njia keyboard, pato kiwango ina maana screen,

438
00:27:02,730 --> 00:27:06,920
na kiwango makosa, ambayo tutaweza kuona katika pset 4, ina maana screen,

439
00:27:06,920 --> 00:27:09,670
lakini sehemu maalum ya screen ili siyo conflated

440
00:27:09,670 --> 00:27:13,760
na pato halisi kwamba wewe nia ya magazeti, lakini zaidi juu ya kwamba katika siku zijazo.

441
00:27:13,760 --> 00:27:19,430
Hivyo fgetc njia tu kusoma moja tabia kutoka keyboard, na kuhifadhi wapi?

442
00:27:19,430 --> 00:27:24,000
Kuhifadhi katika c, na kisha kuangalia, hivyo mimi nina kutumia tu kuhusianisha baadhi ya bulin hapa,

443
00:27:24,000 --> 00:27:28,430
kuangalia kwamba hana sawa \ n, hivyo user ina hit kuingia.

444
00:27:28,430 --> 00:27:31,510
Tunataka kukomesha saa kwamba uhakika, mwisho wa kitanzi, na sisi pia wanataka kuangalia

445
00:27:31,510 --> 00:27:36,170
kwa mara kwa mara maalum, EOF, ambayo kama unajua au nadhani - ni nini kusimama kwa?

446
00:27:36,170 --> 00:27:39,860
Mwisho wa faili. Hivyo hii ni aina ya kiupuzi, kwa sababu kama mimi nina kuandika katika keyboard,

447
00:27:39,860 --> 00:27:41,900
kuna kweli hakuna faili kushiriki katika hili,

448
00:27:41,900 --> 00:27:44,330
lakini hii tu ya aina ya muda generic kutumika kwa maana ya

449
00:27:44,330 --> 00:27:50,320
kwamba kitu kingine ni kuja kutoka kwa vidole binadamu. EOF. Mwisho wa faili.

450
00:27:50,320 --> 00:27:52,600
Kama kando, kama wameweza milele hit kudhibiti d katika keyboard yako,

451
00:27:52,600 --> 00:27:54,680
si kwamba ungependa kuwa bado; ve hit kudhibiti c.

452
00:27:54,680 --> 00:27:57,920
Lakini kudhibiti d zituma hii maalum ya mara kwa mara huitwa EOF.

453
00:27:57,920 --> 00:28:03,100
>> Hivyo sasa sisi tu baadhi ya nguvu ya kumbukumbu mgao.

454
00:28:03,100 --> 00:28:06,460
Hivyo kama n + 1> uwezo, sasa mimi itabidi kueleza n.

455
00:28:06,460 --> 00:28:09,380
n ni jinsi tu wengi ka ni sasa katika buffer,

456
00:28:09,380 --> 00:28:11,970
kamba kwamba wewe sasa kujenga kutoka kwa mtumiaji.

457
00:28:11,970 --> 00:28:16,240
Kama una zaidi ya wahusika katika buffer yako kuliko wewe kuwa na uwezo katika buffer,

458
00:28:16,240 --> 00:28:20,760
intuitively, tunachotaka kufanya ni basi kutenga zaidi ya uwezo.

459
00:28:20,760 --> 00:28:24,490
Mimi naenda skim juu ya baadhi ya hesabu hapa

460
00:28:24,490 --> 00:28:26,900
na lengo tu juu ya kazi hii hapa.

461
00:28:26,900 --> 00:28:29,170
Unajua nini malloc ni, au angalau kwa ujumla ukoo.

462
00:28:29,170 --> 00:28:32,380
Kuchukua nadhani nini realloc gani. [Mwanafunzi jibu, unintelligible]

463
00:28:32,380 --> 00:28:35,690
>> Yeah. Na si kabisa kuongeza kumbukumbu; ni reallocates kumbukumbu kama ifuatavyo:

464
00:28:35,690 --> 00:28:40,530
Kama bado kuna chumba katika mwisho wa kamba kukupa zaidi ya kumbukumbu ya kwamba

465
00:28:40,530 --> 00:28:43,370
kuliko awali inakupa, kisha utapata kwamba kumbukumbu ya ziada.

466
00:28:43,370 --> 00:28:46,640
Hivyo unaweza kuweka tu wahusika masharti nyuma kwa nyuma kwa nyuma kwa nyuma.

467
00:28:46,640 --> 00:28:49,290
Lakini kama si kwamba kesi, kwa sababu wewe walisubiri muda mrefu sana

468
00:28:49,290 --> 00:28:51,700
na kitu random got plopped katika kumbukumbu huko, lakini kuna ziada

469
00:28:51,700 --> 00:28:56,480
kumbukumbu hapa chini, hiyo ni sawa. Realloc anaenda kufanya kuinua nzito kwa ajili yenu,

470
00:28:56,480 --> 00:28:58,810
hoja string umeisoma katika hivi sasa kutoka hapa,

471
00:28:58,810 --> 00:29:02,550
kuiweka chini huko, na kisha kukupa baadhi zaidi Runway katika hatua hiyo.

472
00:29:02,550 --> 00:29:05,610
Hivyo, pamoja na wimbi la mkono, basi mimi kusema kwamba kile GetString ni kufanya

473
00:29:05,610 --> 00:29:09,540
ni ni kwa kuanzia na buffer ndogo, labda 1 moja tabia,

474
00:29:09,540 --> 00:29:12,300
na kama mtumiaji aina katika wahusika 2, GetString inaishia

475
00:29:12,300 --> 00:29:15,210
wito realloc na anasema, 'Ooh, 1 tabia ilikuwa haitoshi.

476
00:29:15,210 --> 00:29:18,480
Nipe wahusika 2. ' Kisha kama kusoma kwa njia ya mantiki ya kitanzi,

477
00:29:18,480 --> 00:29:21,070
itakavyo kusema, 'Ooh, mtumiaji typed katika herufi 3.

478
00:29:21,070 --> 00:29:25,690
Nipe sasa si 2 lakini 4 wahusika, basi nipe 8, basi nipe 16 na 32. '

479
00:29:25,690 --> 00:29:28,180
ukweli kwamba mimi nina uwezo mara dufu kila wakati

480
00:29:28,180 --> 00:29:30,320
ina maana kwamba buffer si kwenda kukua polepole.

481
00:29:30,320 --> 00:29:35,870
Ni kwenda kukua super kufunga, na nini inaweza kuwa faida ya kwamba?

482
00:29:35,870 --> 00:29:38,540
Kwa nini mimi mara mbili ya ukubwa wa buffer, ingawa mtumiaji

483
00:29:38,540 --> 00:29:41,450
ili tu haja 1 ziada tabia kutoka keyboard?

484
00:29:41,450 --> 00:29:44,830
[Mwanafunzi jibu, unintelligible]. >> Gani hiyo?

485
00:29:44,830 --> 00:29:46,750
Hasa. Huna kukua ni kama mara nyingi.

486
00:29:46,750 --> 00:29:48,870
Na hii ni aina tu ya - you're Hedging bets yako hapa.

487
00:29:48,870 --> 00:29:54,150
wazo kuwa kuwa hutaki kuwaita realloc mengi, kwa sababu huelekea kuwa polepole.

488
00:29:54,150 --> 00:29:56,840
Wakati wowote kuuliza mfumo wa uendeshaji kwa ajili ya kumbukumbu, kama utasikia haraka kuona

489
00:29:56,840 --> 00:30:00,620
katika kuweka baadaye tatizo, huelekea kuchukua muda.

490
00:30:00,620 --> 00:30:04,980
Hivyo kukanusha kwamba kiasi cha muda, hata kama wewe ni kupoteza baadhi ya nafasi, huelekea kuwa ni jambo jema.

491
00:30:04,980 --> 00:30:07,250
>> Lakini kama sisi kusoma kupitia sehemu ya mwisho ya GetString hapa,

492
00:30:07,250 --> 00:30:10,880
na tena, kuelewa kila line moja hapa sio muhimu leo.

493
00:30:10,880 --> 00:30:14,830
Lakini ona kwamba hatimaye wito malloc tena, na kutenga

494
00:30:14,830 --> 00:30:16,980
hasa kama ka wengi kama ni mahitaji kwa kamba

495
00:30:16,980 --> 00:30:21,620
na kisha throws mbali na wito bure, buffer kupita kiasi kikubwa,

496
00:30:21,620 --> 00:30:23,510
kama ni kweli got mara mbili mara nyingi sana.

497
00:30:23,510 --> 00:30:25,970
Kwa kifupi, hiyo ni jinsi GetString imekuwa ikifanya kazi muda wote huu.

498
00:30:25,970 --> 00:30:30,100
All yake ni kusoma moja ya tabia kwa wakati tena na tena na tena

499
00:30:30,100 --> 00:30:37,930
na kila wakati inahitaji baadhi ya kumbukumbu ya ziada, inauliza mfumo wa uendeshaji kwa ajili yake kwa wito realloc.

500
00:30:37,930 --> 00:30:41,660
Maswali yoyote? Wote haki.

501
00:30:41,660 --> 00:30:45,220
>> mashambulizi. Sasa kwa kuwa tunaelewa kuyatumia, au angalau

502
00:30:45,220 --> 00:30:47,560
zinazidi ukoo na kuyatumia,

503
00:30:47,560 --> 00:30:50,020
hebu fikiria jinsi dunia zima kuanza kuanguka

504
00:30:50,020 --> 00:30:53,160
kama huna kabisa kulinda dhidi ya watumiaji adversarial,

505
00:30:53,160 --> 00:30:55,180
watu ambao ni kujaribu Hack ndani ya mfumo wako.

506
00:30:55,180 --> 00:31:00,260
Watu ambao ni kujaribu kuiba programu yako kwa circumventing baadhi ya kanuni za usajili

507
00:31:00,260 --> 00:31:02,150
wapate kuwa vinginevyo na aina in

508
00:31:02,150 --> 00:31:04,860
Kuangalia mfano huu hapa, ambayo ni tu C code

509
00:31:04,860 --> 00:31:07,920
kwamba ina kazi kuu chini, kwamba wito foo kazi,

510
00:31:07,920 --> 00:31:12,100
na kile ni kupitisha foo? [Mwanafunzi] hoja moja.

511
00:31:12,100 --> 00:31:15,660
>> Single hoja. Hivyo argv [1], ambayo ina maana ya neno kwanza mtumiaji typed

512
00:31:15,660 --> 00:31:19,150
katika mstari amri baada a.out au chochote mpango inaitwa.

513
00:31:19,150 --> 00:31:24,920
Hivyo foo, saa ya juu, inachukua katika * Char, lakini * Char ni yale tu?

514
00:31:24,920 --> 00:31:28,860
Kamba. Kuna kitu kipya hapa, na kamba kwamba ni kiholela kuitwa bar.

515
00:31:28,860 --> 00:31:36,090
Katika mstari huu hapa, char c [12], katika aina ya nusu ya kiufundi Kiingereza, ni nini mstari huu kufanya?

516
00:31:36,090 --> 00:31:40,640
Safu ya -? Nyingine. Nipe safu ya wahusika 12.

517
00:31:40,640 --> 00:31:44,970
Hivyo tupate wito huu buffer. Ni kitaalam inaitwa c, lakini buffer katika programu

518
00:31:44,970 --> 00:31:47,890
njia tu rundo la nafasi kuwa unaweza kuweka baadhi ya mambo in

519
00:31:47,890 --> 00:31:49,940
>> Kisha mwisho, memcpy, tumekuwa si kutumika kabla.

520
00:31:49,940 --> 00:31:52,380
Lakini pengine unaweza nadhani nini inakuwa hivyo. Ni nakala ya kumbukumbu.

521
00:31:52,380 --> 00:31:58,790
Ni nini nini? Naam, ni dhahiri nakala bar, mchango wake, katika c,

522
00:31:58,790 --> 00:32:03,420
lakini tu hadi urefu wa bar.

523
00:32:03,420 --> 00:32:07,440
Lakini kuna mdudu hapa.

524
00:32:07,440 --> 00:32:14,500
Okay, hivyo kitaalam tunatakiwa kufanya strlen (bar) x sizeof (Char), kwamba ni sahihi.

525
00:32:14,500 --> 00:32:17,920
Lakini katika hali mbaya hapa, hebu kudhani kwamba that's - hivyo, okay.

526
00:32:17,920 --> 00:32:23,760
Kisha kuna 2 mende. Hivyo sizeof (Char), wote haki, wacha kufanya hii kidogo pana.

527
00:32:23,760 --> 00:32:28,860
Hivyo sasa bado kuna mdudu, ambayo ni nini?

528
00:32:28,860 --> 00:32:31,630
[Mwanafunzi jibu, unintelligible] >> Check kwa nini? Okay, kwa hivyo sisi inapaswa kuangalia

529
00:32:31,630 --> 00:32:35,010
kwa null, kwa sababu mambo mabaya kutokea wakati pointer yako ni null,

530
00:32:35,010 --> 00:32:38,490
Kwa sababu unaweza kuishia kwenda huko, na unapaswa si milele kuwa kwenda kwa null

531
00:32:38,490 --> 00:32:40,890
na dereferencing kwa operator *.

532
00:32:40,890 --> 00:32:45,250
Basi hiyo ni nzuri, na kile kingine ni sisi kufanya? Kimantiki kuna flaw hapa pia.

533
00:32:45,250 --> 00:32:47,650
[Mwanafunzi jibu, unintelligible]

534
00:32:47,650 --> 00:32:51,340
>> Hivyo kuangalia kama argc ≥ 2?

535
00:32:51,340 --> 00:32:54,130
Okay, hivyo kuna 3 mende katika mpango huu hapa.

536
00:32:54,130 --> 00:33:00,080
Sisi siyo kuangalia kama mtumiaji kweli typed katika kitu chochote ndani ya argv [1], nzuri.

537
00:33:00,080 --> 00:33:02,240
Basi nini mdudu wa tatu? Yeah?

538
00:33:02,240 --> 00:33:04,420
[Mwanafunzi jibu, unintelligible] >> Good.

539
00:33:04,420 --> 00:33:09,590
Hivyo sisi tulienda moja tukio. Sisi implicitly checked usinakili zaidi ya kumbukumbu

540
00:33:09,590 --> 00:33:12,800
kuliko ingekuwa kisichozidi urefu wa bar.

541
00:33:12,800 --> 00:33:15,720
Hivyo kama string mtumiaji typed katika ni 10 wahusika muda mrefu,

542
00:33:15,720 --> 00:33:18,260
hii ni kusema, 'tu nakala wahusika 10.'

543
00:33:18,260 --> 00:33:21,140
Na hiyo ni sawa, lakini kile kama mtumiaji typed katika neno katika kuchochea

544
00:33:21,140 --> 00:33:29,360
kama neno 20 tabia, hii ni, akisema nakala wahusika 20 kutoka bar ndani ya nini?

545
00:33:29,360 --> 00:33:32,840
c, inayojulikana kama buffer yetu, ambayo ina maana tu aliandika data

546
00:33:32,840 --> 00:33:35,950
hadi 8 Byte maeneo ambayo huna mwenyewe,

547
00:33:35,950 --> 00:33:38,320
na humiliki yao kwa maana ya kwamba kamwe zilizotengwa kwao.

548
00:33:38,320 --> 00:33:41,190
Hivyo hii ni nini ujumla inayojulikana kama mashambulizi ya kufurika buffer,

549
00:33:41,190 --> 00:33:46,650
au buffer overrun mashambulizi, na mashambulizi yake kwa maana kwamba kama mtumiaji

550
00:33:46,650 --> 00:33:50,650
au mpango hiyo wito kazi yako ni kufanya hii maliciously,

551
00:33:50,650 --> 00:33:53,780
nini hasa kinatokea ijayo inaweza kuwa mbaya kabisa.

552
00:33:53,780 --> 00:33:55,690
>> Hebu tuangalie picha hii hapa.

553
00:33:55,690 --> 00:33:59,070
Hii picha inawakilisha stack yako ya kumbukumbu.

554
00:33:59,070 --> 00:34:01,050
Na kukumbuka kwamba kila wakati wewe piga kazi,

555
00:34:01,050 --> 00:34:04,520
kupata sura hii kidogo juu ya stack na kisha mwingine na kisha mwingine na kisha mwingine.

556
00:34:04,520 --> 00:34:07,250
Na hivi sasa tumekuwa aina tu ya abstracted hizi mbali kama mistatili

557
00:34:07,250 --> 00:34:09,380
aidha kuna ubaoni au kwenye screen hapa.

558
00:34:09,380 --> 00:34:12,219
Lakini kama sisi zoom katika kwenye moja ya mistatiri hizo,

559
00:34:12,219 --> 00:34:16,460
wakati wewe piga foo kazi, zinageuka kuwa kuna zaidi juu ya stack

560
00:34:16,460 --> 00:34:18,739
ndani ya kwamba sura na kwamba Mstatili

561
00:34:18,739 --> 00:34:23,370
kuliko tu x na y na a na b, kama sisi hawakuwa kuzungumza juu ya kubadilishana.

562
00:34:23,370 --> 00:34:25,949
Ni zinageuka kuwa kuna baadhi ya maelezo ya chini ya ngazi,

563
00:34:25,949 --> 00:34:27,780
kati yao kurudi anuani.

564
00:34:27,780 --> 00:34:33,020
Hivyo zinageuka wakati kuu wito foo, kuu ina kuwajulisha foo

565
00:34:33,020 --> 00:34:36,760
nini anwani kuu ni katika kumbukumbu ya kompyuta.

566
00:34:36,760 --> 00:34:40,659
Kwa sababu vinginevyo, kwa haraka kama foo inafanywa utekelezaji, kama katika kesi hii hapa,

567
00:34:40,659 --> 00:34:43,790
mara moja wewe kufikia hii karibu curly brace mwishoni mwa foo,

568
00:34:43,790 --> 00:34:48,860
jinsi heck haina foo kujua ambapo udhibiti wa mpango zinatakiwa kwenda?

569
00:34:48,860 --> 00:34:52,460
Ni zinageuka kuwa jibu la swali hilo ni katika mstatili kwamba nyekundu hapa.

570
00:34:52,460 --> 00:34:56,130
Hii inawakilisha pointer, na ni juu ya kompyuta kuhifadhi, kwa muda,

571
00:34:56,130 --> 00:35:00,250
juu ya stack kinachojulikana anuani ya kuu ili haraka kama foo inafanywa utekelezaji,

572
00:35:00,250 --> 00:35:04,110
kompyuta anajua wapi na nini line katika kuu ya kwenda nyuma ya.

573
00:35:04,110 --> 00:35:06,900
Kuokolewa frame pointer inahusiana vile vile kwa hii.

574
00:35:06,900 --> 00:35:09,620
Char * bar hapa inawakilisha nini?

575
00:35:09,620 --> 00:35:14,740
Naam, sasa hii sehemu ya bluu hapa ni sura foo, je ni bar?

576
00:35:14,740 --> 00:35:18,300
Okay, kwa hivyo ni bar tu hoja kwa kazi foo.

577
00:35:18,300 --> 00:35:20,720
>> Hivyo sasa tuko nyuma katika picha za ukoo.

578
00:35:20,720 --> 00:35:22,960
Kuna zaidi ya mambo na distractions zaidi juu ya screen

579
00:35:22,960 --> 00:35:27,490
lakini hii mwanga sehemu ya bluu ni nini tumekuwa kuchora ubaoni kwa kitu kama byta.

580
00:35:27,490 --> 00:35:31,890
Hiyo ni sura kwa foo na kitu pekee katika haki sasa ni bar,

581
00:35:31,890 --> 00:35:34,630
ambayo ni hii parameter.

582
00:35:34,630 --> 00:35:39,840
Lakini nini kingine unapaswa kuwa katika stack, kulingana na kanuni hii hapa?

583
00:35:39,840 --> 00:35:44,280
Char c [12]. Hivyo inabidi kuona viwanja 12 ya kumbukumbu,

584
00:35:44,280 --> 00:35:46,260
zilizotengwa kwa ajili ya variable kuitwa c.

585
00:35:46,260 --> 00:35:48,340
Na hakika sisi kufanya kuwa na kwamba kwenye screen.

586
00:35:48,340 --> 00:35:51,650
sana juu kuna c [0], na kisha mwandishi wa mchoro huu

587
00:35:51,650 --> 00:35:55,130
haikujali kuchora wote wa miraba lakini kuna shaka 12 kuna

588
00:35:55,130 --> 00:36:00,120
kwa sababu kama ukiangalia chini kulia, c [11], kama hesabu kutoka 0, ni 12 vile bytes.

589
00:36:00,120 --> 00:36:06,190
Lakini hapa ni tatizo: Katika ambayo mwelekeo ni kuongezeka c?

590
00:36:06,190 --> 00:36:10,390
Aina ya juu chini, sawa? Kama ni kuanza saa ya juu na kukua hadi chini,

591
00:36:10,390 --> 00:36:13,480
haionekani kama sisi kushoto wenyewe Runway sana hapa wakati wote.

592
00:36:13,480 --> 00:36:15,320
Tumekuwa aina ya walijenga wenyewe ndani ya kona,

593
00:36:15,320 --> 00:36:20,210
na kwamba c [11] ni haki juu ya bar, ambayo ni haki ya juu dhidi ya stack pointer frame,

594
00:36:20,210 --> 00:36:23,800
ambayo ni haki juu ya anwani ya kurudi; hakuna nafasi zaidi.

595
00:36:23,800 --> 00:36:26,100
Basi nini maana, basi, kama wewe screw up,

596
00:36:26,100 --> 00:36:30,460
na wewe jaribu kusoma ka 20 ndani ya buffer 12-Byte?

597
00:36:30,460 --> 00:36:33,460
Ambapo ni wale 8 ka ziada kwenda?

598
00:36:33,460 --> 00:36:36,370
Ndani ya kila kitu kingine, ambayo baadhi ni super muhimu.

599
00:36:36,370 --> 00:36:40,480
Na jambo muhimu zaidi, uwezekano, ni sanduku nyekundu huko, kurudi anuani.

600
00:36:40,480 --> 00:36:44,720
Kwa sababu tuseme kwamba wewe ni aidha ajali au adversarially

601
00:36:44,720 --> 00:36:48,040
overwrite ka wale 4, kwamba anuani pointer,

602
00:36:48,040 --> 00:36:53,190
si tu kwa takataka, lakini pamoja na kwamba idadi hiyo hutokea kwa kuwakilisha anuani halisi katika kumbukumbu?

603
00:36:53,190 --> 00:36:55,930
Nini implicaiton, mantiki?

604
00:36:55,930 --> 00:36:59,080
[Mwanafunzi majibu, unintelligible] >> Hasa. Wakati foo anarudi

605
00:36:59,080 --> 00:37:03,560
na hits kwamba brace curly, mpango ni kwenda kuendelea wasimrudie kuu,

606
00:37:03,560 --> 00:37:08,320
itakavyo kurudi chochote anuani ni katika sanduku kwamba nyekundu.

607
00:37:08,320 --> 00:37:11,560
>> Sasa, katika kesi ya usajili circumventing programu,

608
00:37:11,560 --> 00:37:14,400
kile ni anuani ya kwamba ni kuwa alirejea ni kazi

609
00:37:14,400 --> 00:37:18,820
kwamba kwa kawaida anapata kuitwa baada ve kulipwa kwa ajili ya programu na inputted usajili wako code?

610
00:37:18,820 --> 00:37:23,160
Unaweza aina ya hila ya kompyuta katika si kwenda hapa, lakini badala yake, anakwenda hapa.

611
00:37:23,160 --> 00:37:27,950
Au, kama wewe ni kweli wajanja, adui unaweza kweli aina katika saa keyboard,

612
00:37:27,950 --> 00:37:32,500
kwa mfano, si neno halisi, wahusika si 20, lakini nadhani yeye au yeye

613
00:37:32,500 --> 00:37:36,200
aina katika baadhi ya wahusika kwamba kuwakilisha code?

614
00:37:36,200 --> 00:37:38,860
Na si kwenda kuwa C kificho, ni kwenda kuwa wahusika

615
00:37:38,860 --> 00:37:42,920
kwamba kuwakilisha codes mashine binary, 0 na 1 ya.

616
00:37:42,920 --> 00:37:46,740
Lakini tuseme wao uko wajanja kutosha kufanya hivyo, kwa namna fulani kuweka katika haraka GetString

617
00:37:46,740 --> 00:37:49,460
kitu ambacho kimsingi ni compiled kificho,

618
00:37:49,460 --> 00:37:56,900
na mwisho 4 ka overwrite kwamba anuani kurudi, na nini anwani haina pembejeo kwamba kufanya?

619
00:37:56,900 --> 00:38:01,860
Ni maduka katika mstatili hii nyekundu anuani ya Byte kwanza ya buffer.

620
00:38:01,860 --> 00:38:04,270
Hivyo wewe kuwa kweli wajanja, na hii ni mengi ya kesi na makosa

621
00:38:04,270 --> 00:38:08,500
kwa watu mbaya huko nje, lakini kama unaweza kufikiri ni jinsi gani kubwa buffer hii ni,

622
00:38:08,500 --> 00:38:12,170
vile kwamba mwisho ka chache katika pembejeo kwamba wewe kutoa kwa mpango

623
00:38:12,170 --> 00:38:15,970
kutokea kwa kuwa sawa na anuani ya mwanzo wa buffer yako,

624
00:38:15,970 --> 00:38:22,270
unaweza kufanya hivyo. Tukisema, kwa kawaida, hello, na \ 0, kwamba ni nini mwisho juu katika buffer.

625
00:38:22,270 --> 00:38:27,860
Lakini kama tupo zaidi wajanja, na sisi kujaza kwamba buffer na kile tutaweza generically kuwaita mashambulizi kificho,

626
00:38:27,860 --> 00:38:31,920
,,,: Attack, mashambulizi, mashambulizi, mashambulizi, ambapo hii ni tu kitu ambacho hana kitu mbaya.

627
00:38:31,920 --> 00:38:35,190
Naam, kile kinachotokea kama wewe ni kweli wajanja, unaweza kufanya kazi hii:

628
00:38:35,190 --> 00:38:41,740
Katika sanduku nyekundu hapa ni mlolongo wa namba: 80, CO, 35, 08.

629
00:38:41,740 --> 00:38:44,890
Ona kwamba kuwa mechi ya idadi hiyo ni hapa juu.

630
00:38:44,890 --> 00:38:47,280
Ni katika utaratibu reverse, lakini zaidi juu ya wakati kwamba baadhi nyingine.

631
00:38:47,280 --> 00:38:51,430
Ona kwamba anuani hii kurudi imekuwa makusudi ilibadilika

632
00:38:51,430 --> 00:38:54,970
kwa anuani sawa hapa, si anuani ya kuu.

633
00:38:54,970 --> 00:39:00,170
Hivyo kama mtu mbaya ni super smart, yeye au yeye ni kwenda kwa pamoja katika kificho kwamba mashambulizi

634
00:39:00,170 --> 00:39:02,890
kitu kama, 'Futa wote wa files mtumiaji.'

635
00:39:02,890 --> 00:39:06,320
Au 'Nakili nywila,' au 'Fungua akaunti ya mtumiaji kwamba naweza kuingia ndani.'

636
00:39:06,320 --> 00:39:10,130
Chochote wakati wote, na hii ni hatari zote na nguvu ya C.

637
00:39:10,130 --> 00:39:12,900
Kwa sababu unaweza kupata kumbukumbu kupitia kuyatumia

638
00:39:12,900 --> 00:39:15,950
na kwa hiyo unaweza kuandika kitu chochote unataka ndani ya kumbukumbu ya kompyuta.

639
00:39:15,950 --> 00:39:19,290
Unaweza kufanya kompyuta kufanya kitu chochote unataka tu na

640
00:39:19,290 --> 00:39:22,780
baada yake kuruka karibu ndani ya nafasi yake mwenyewe kumbukumbu.

641
00:39:22,780 --> 00:39:27,230
Na hivyo, kwa leo, hivyo wengi mipango na tovuti nyingi kwamba ni kuathirika

642
00:39:27,230 --> 00:39:29,730
chemsha chini ya watu kuchukua faida ya hii.

643
00:39:29,730 --> 00:39:32,510
Na hii inaweza kuonekana kama mashambulizi super-kisasa,

644
00:39:32,510 --> 00:39:34,220
lakini haina daima kuanza kwa njia hiyo.

645
00:39:34,220 --> 00:39:36,770
>> ukweli ni kwamba watu wabaya itakuwa kawaida kufanya ni,

646
00:39:36,770 --> 00:39:41,470
kama ni mpango katika mstari amri au mpango GUI au tovuti,

647
00:39:41,470 --> 00:39:43,290
ni wewe tu kuanza kutoa nonsense.

648
00:39:43,290 --> 00:39:46,940
Wewe aina katika neno kubwa kweli kweli ndani ya shamba tafuta na hit kuingia,

649
00:39:46,940 --> 00:39:49,030
na kusubiri kuona kama shambulio tovuti.

650
00:39:49,030 --> 00:39:53,270
Au wewe kusubiri kuona kama mpango hudhihirisha baadhi ujumbe wa kosa.

651
00:39:53,270 --> 00:39:55,480
Kwa sababu kama wewe kupata bahati, kama mtu mbaya,

652
00:39:55,480 --> 00:39:59,610
na wewe kutoa baadhi ya pembejeo crazy kwamba shambulio mpango,

653
00:39:59,610 --> 00:40:02,280
kwamba maana ya programu Hawakutarajia tabia yako mbaya

654
00:40:02,280 --> 00:40:05,420
ambayo ina maana unaweza pengine, na juhudi za kutosha,

655
00:40:05,420 --> 00:40:09,870
kutosha kesi na makosa, kufikiri jinsi ya kupigana mashambulizi sahihi zaidi.

656
00:40:09,870 --> 00:40:15,900
Hivyo kama sehemu kubwa ya usalama si tu kuepuka mashambulizi haya kabisa, lakini kuchunguza yao

657
00:40:15,900 --> 00:40:20,250
na kwa kweli kuangalia magogo na kuona ni nini pembejeo mambo kuwa watu typed katika tovuti yako.

658
00:40:20,250 --> 00:40:26,040
Nini tafuta masharti kuwa watu typed katika tovuti yako kwa matumaini ya kufurika baadhi buffer?

659
00:40:26,040 --> 00:40:28,900
Na hii yote majipu chini misingi rahisi ya nini safu,

660
00:40:28,900 --> 00:40:32,510
na nini maana ya kutenga na kutumia kumbukumbu?

661
00:40:32,510 --> 00:40:34,920
Na kuhusiana na kwamba, pia, ni hii.

662
00:40:34,920 --> 00:40:37,520
>> Basi hebu tu mtazamo ndani ya gari ngumu bado tena.

663
00:40:37,520 --> 00:40:40,190
Hivyo, unakumbuka kutoka wiki moja au mbili zilizopita kwamba wakati wewe Drag files

664
00:40:40,190 --> 00:40:45,470
kwa yako kusaga bin au takataka unaweza, nini kitatokea?

665
00:40:45,470 --> 00:40:47,850
[Mwanafunzi] Hakuna. >> Yeah, kitu kabisa. Hatimaye kama wewe kukimbia chini

666
00:40:47,850 --> 00:40:51,370
juu ya nafasi disk, Windows au Mac OS itaanza kufuta faili kwa ajili yenu.

667
00:40:51,370 --> 00:40:53,670
Lakini kama wewe Drag kitu huko, basi ni si wakati wote salama.

668
00:40:53,670 --> 00:40:56,550
Yako yote roomate, rafiki au familia ina kufanya ni bonyeza mara mbili, na voilà.

669
00:40:56,550 --> 00:40:59,720
Kuna mafaili yote sketchy kwamba alijaribu kufuta.

670
00:40:59,720 --> 00:41:02,840
Hivyo wengi wetu angalau kujua kwamba una haki bonyeza au kudhibiti click

671
00:41:02,840 --> 00:41:05,320
na tupu takataka, au kitu kama hicho.

672
00:41:05,320 --> 00:41:07,900
Lakini hata hivyo, kwamba hana kabisa kufanya hila.

673
00:41:07,900 --> 00:41:11,340
Kwa sababu kile kinachotokea wakati una faili kwenye gari yako ngumu

674
00:41:11,340 --> 00:41:14,590
kwamba inawakilisha baadhi ya hati neno au baadhi JPEG?

675
00:41:14,590 --> 00:41:18,820
Na hii inawakilisha gari yako ngumu, na hebu sema hii Sliver hapa inawakilisha kwamba faili,

676
00:41:18,820 --> 00:41:21,640
na ni linajumuisha rundo zima la wa 0 na 1 ya.

677
00:41:21,640 --> 00:41:25,470
Nini kinatokea wakati wewe si tu Drag kwamba faili trashcan au kusaga bin,

678
00:41:25,470 --> 00:41:30,390
lakini pia ni tupu?

679
00:41:30,390 --> 00:41:32,820
Aina ya kitu. Ni si kitu kabisa sasa.

680
00:41:32,820 --> 00:41:37,630
Sasa ni kitu tu, kwa sababu kitu kidogo kinachotokea katika fomu ya meza hii.

681
00:41:37,630 --> 00:41:41,170
Hivyo kuna baadhi ya aina ya database au meza ndani ya kumbukumbu ya kompyuta

682
00:41:41,170 --> 00:41:44,470
kwamba kimsingi ina 1 safu kwa majina files,

683
00:41:44,470 --> 00:41:50,550
na 1 safu kwa ajili ya eneo faili, ambapo hii inaweza kuwa mahali 123, tu idadi random.

684
00:41:50,550 --> 00:41:58,270
Hivyo sisi tupate kuwa na kitu kama x.jpg, na mahali 123.

685
00:41:58,270 --> 00:42:02,870
Na kile kinachotokea basi, wakati wewe tupu takataka yako?

686
00:42:02,870 --> 00:42:06,720
Kwamba huenda mbali. Lakini ni nini si kwenda mbali ni ya 0 na 1 ya.

687
00:42:06,720 --> 00:42:09,690
>> Basi nini, basi, uhusiano na pset 4?

688
00:42:09,690 --> 00:42:13,460
Naam, na pset 4, kwa sababu tu tumekuwa ajali erased

689
00:42:13,460 --> 00:42:15,890
kompakt flash kadi kwamba alikuwa zote za picha hizi,

690
00:42:15,890 --> 00:42:18,710
au kwa sababu tu kwa bahati mbaya akawa kupotoshwa,

691
00:42:18,710 --> 00:42:21,170
haina maana kwamba 0 na 1 ni si bado kuna.

692
00:42:21,170 --> 00:42:23,920
Labda wachache wao ni kupotea kwa sababu kitu got kupotoshwa

693
00:42:23,920 --> 00:42:26,530
kwa maana kwamba baadhi ya 0 1 akawa na 1 akawa 0 wa.

694
00:42:26,530 --> 00:42:30,460
Mambo mabaya yanaweza kutokea kwa sababu ya programu Buggy au defective vifaa.

695
00:42:30,460 --> 00:42:33,510
Lakini wengi wa bits wale, labda hata 100% ya nao ni bado kuna,

696
00:42:33,510 --> 00:42:38,330
ni kwamba tu kompyuta au kamera hajui ambapo JPEG 1 ilianza

697
00:42:38,330 --> 00:42:41,660
na ambapo JPEG 2 kuanza, lakini kama wewe, programu,

698
00:42:41,660 --> 00:42:45,800
kujua, na kidogo ya savvy, ambapo wale JPEGs ni nini au kuangalia kama,

699
00:42:45,800 --> 00:42:49,570
unaweza kuchanganua ya 0 na 1 na kusema, 'Ooh. JPEG. Ooh, JPEG. '

700
00:42:49,570 --> 00:42:52,830
Unaweza kuandika mpango na kimsingi tu kwa wakati au kitanzi

701
00:42:52,830 --> 00:42:56,100
kwamba recovers kila mmoja na kila mmoja wa wale files.

702
00:42:56,100 --> 00:42:59,360
Hivyo somo basi, ni kuanza "salama" erasing files yako

703
00:42:59,360 --> 00:43:01,720
kama Ningependa ili kuepuka hili kabisa. Ndiyo?

704
00:43:01,720 --> 00:43:06,940
[Mwanafunzi swali, unintelligible]

705
00:43:06,940 --> 00:43:11,150
>> Je kumbukumbu zaidi kuliko alivyofanya kabla -

706
00:43:11,150 --> 00:43:14,790
Oh! Nzuri swali. Hivyo kwa nini, basi, baada ya kuingia takataka,

707
00:43:14,790 --> 00:43:18,300
haina kompyuta yako kukuambia kwamba una zaidi bure nafasi kuliko wewe alifanya mbele?

708
00:43:18,300 --> 00:43:22,450
Kwa kifupi, kwa sababu ni uongo. Zaidi ya kitaalam, una nafasi zaidi.

709
00:43:22,450 --> 00:43:26,720
Kwa sababu sasa wewe kuwa alisema, unaweza kuweka mambo mengine ambapo faili kwamba mara alikuwa,

710
00:43:26,720 --> 00:43:28,930
lakini hiyo haina maana bits ni kwenda mbali,

711
00:43:28,930 --> 00:43:33,070
na hiyo haina maana bits ni kuwa iliyopita wote 0, kwa mfano, kwa kinga yako.

712
00:43:33,070 --> 00:43:37,520
Kwa kulinganisha, kama wewe "salama" erase files, au kimwili kuharibu kifaa,

713
00:43:37,520 --> 00:43:40,810
kwamba kweli ni njia pekee, wakati mwingine, kuzunguka kwamba.

714
00:43:40,810 --> 00:43:45,300
Hivyo kwa nini sisi kuondoka kwamba kumbuka nusu inatisha, na sisi kuona juu ya Jumatatu.

715
00:43:45,300 --> 00:43:52,810
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