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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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>> Hii ni CS50, Wiki 5.

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Leo na wiki hii, sisi kuanzisha kidogo ya dunia ya forensics

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katika muktadha wa Matatizo Kuweka 4.

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Leo itakuwa hotuba abbreviated kwa sababu kuna tukio maalum katika hapa baadaye.

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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 mit mpya online mpango kwa OpenCourseWare na zaidi,

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ni uzinduzi juu ya chuo cha Harvard juu ya Jumatatu, ambayo ina maana ya kuja Jumatatu

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utakuwa kama wa hesabu ya mwisho, 86,000 classmates ziada

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ambao watakuwa kufuatia pamoja na mihadhara CS50 na sehemu

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na walkthroughs na seti tatizo.

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

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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 shirika amri-line ndani ya appliance

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kwamba utapata mara moja update baadaye wiki hii.

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Wewe utakuwa na uwezo wa kukimbia amri, check50, juu ya pset yako mwenyewe,

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na utasikia kupata maoni ya papo ya kama mpango wako ni sahihi au si sahihi

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kulingana na design mbalimbali specifikationer kwamba tuna zinazotolewa.

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Zaidi juu ya kwamba katika vipimo kuweka tatizo.

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Classmates CS50x itakuwa kutumia hii kama vile.

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>> Tatizo Set 4 ni wote kuhusu forensics,

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na pset hii ilikuwa kweli aliongoza kwa baadhi ya mambo halisi ya maisha

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ambapo nilipokuwa katika shule ya kuhitimu mimi interned kwa wakati

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na ofisi ya Middlesex Jina la Wilaya ya Mwanasheria kufanya kazi ya kuchunguza mauaji

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na mpelelezi wao risasi kuchunguza mauaji.

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Nini hii yalifikia, kama nilivyoeleza nadhani wiki chache zilizopita,

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ni Jimbo Misa Polisi au wengine atakuja katika,

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

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na kisha lengo la ofisi forensics ilikuwa kuhakikisha

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kama kuna 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, kitu chochote kuwashirikisha baadhi ya aina ya vyombo vya habari digital.

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Ni zinageuka kuwa siyo kwamba watu wengi kuandika barua pepe akisema, "Mimi alifanya hivyo."

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Hivyo mara nyingi kabisa, upekuzi kuchunguza mauaji 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, jitihada walipewa zawadi.

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>> Lakini kuwaongoza hadi pset hii ya kuchunguza mauaji, tutaweza kuwa kuanzisha katika pset4 kidogo ya graphics.

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Wewe pengine kuchukua mambo haya kwa alimjalia - 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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Katika kesi ya uso wa Rob, kuna kila aina ya rangi,

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

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mara moja tulianza zoom in

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

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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.

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11000011 inawakilisha nyeupe, nyeupe, nyeusi, nyeusi, nyeusi, nyeusi, nyeupe, nyeupe.

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Na hivyo si leap kubwa kisha kuanza kuzungumza juu ya picha ya rangi,

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mambo kwamba Ningependa kuona kwenye Facebook au kuchukua na kamera digital.

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Lakini bila ya shaka 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 Set 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 kesho kawaida.

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>> Tutaweza pia kuanzisha wewe format faili nyingine.

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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 kusaidiwa wanatangaza hii format

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kuitwa bitmap faili format, bmp, na hii ilikuwa super rahisi, colourful graphical faili format

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kwamba ilitumika kwa muda kabisa 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 picha bmp au bitmap.

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

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Ni kabisa kama rahisi kama hii gridi ya sekunde 0 na 1s.

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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 sekunde 0 na 1s,

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lakini kuna baadhi ya ziada na sekunde 0 1s 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, mp4., chochote format faili

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kwamba wewe ni ukoo na - ni nini hata maana ya kuwa format ya SVG,

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kwa sababu mwisho wa siku wote wa files haya sisi kutumia tu kuwa na sekunde 0 na 1s.

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Na labda wale sekunde 0 na 1s kuwakilisha ABC kupitia ASCII au kama,

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lakini mwisho wa siku, bado tu sekunde 0 na 1s.

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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 0 kukabiliana huko,

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huko ni 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 ni hii.

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

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ina mfano wa sekunde 0 na 1s kwamba inawakilisha nini? ukubwa wa kitu fulani.

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Na unaendelea kutoka huko.

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Hivyo katika Tatizo Set 4, wewe utakuwa kutembea kwa njia ya baadhi ya mambo haya.

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Sisi si kuishia kujali juu yao wote.

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Lakini taarifa hiyo kuanza kupata kuvutia karibu 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 moja mwanga mkali kuja nje ya Lens,

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lakini nyuma katika siku alikuwa na Lens nyekundu, Lens bluu, na Lens ya 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 hivyo kidogo potovu, hivyo walikuwa aina ya kuona picha mara mbili au tatu.

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Lakini hiyo ilikuwa 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 basi miongoni mwa changamoto kwa ajili yenu katika Tatizo Set 4 ni kwenda kuwa mambo kadhaa.

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Moja ni kweli resize picha, kuchukua katika muundo wa sekunde 0 na 1s,

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kufikiri ambayo chunks ya sekunde 0 na 1s 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,

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inaweza kuangalia kama hii badala baada ya hapo.

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Miongoni mwa changamoto nyingine pia ni kwenda kuwa kuwa wewe utakuwa mitupu picha ya kuchunguza mauaji

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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 na kamera digital.

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Na hivyo sisi haraka kunakiliwa wote wa mbali na sekunde 0 1s ya kadi ya kwamba kwa ajili yenu,

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akawaokoa wote katika faili moja kubwa, na kisha tutaweza mkono wao na wewe katika Tatizo Set 4

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hivyo kwamba unaweza kuandika mpango katika C na ambayo kuokoa wote wa JPEGs hizo, walau.

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

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wao uko magumu zaidi kuliko uso hii smiling hapa -

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zinageuka kuwa kila JPEG kuanza na mwelekeo huo wa sekunde 0 na 1s.

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Hivyo kutumia, hatimaye, kitanzi wakati au kwa kitanzi au sawa,

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unaweza iterate juu ya yote na sekunde 0 1s katika picha hii ya kuchunguza mauaji,

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

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unaweza kudhani hapa ni pamoja na uwezekano juu sana, mwanzo wa JPEG.

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Na haraka kama wewe kupata mfano huo baadhi idadi ya ka

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au kilobytes au megabaiti baadaye, unaweza kudhani hapa ni JPEG pili,

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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 pset4 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 tutakuwa kabisa kesi ya kawaida.

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Basi hiyo ni nini juu ya upeo wa macho.

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>> Maswali 0 nyuma yetu, kwa kutambua email yangu kwamba invariably kuna folks ambao ni wawili na furaha,

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aina ya wakati upande wowote, na kusikitisha kuzunguka Jaribio 0.

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Na tafadhali kufikia nje kwangu, kichwa TF 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, ni nini maktaba CS50?

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[Kicheko] Kazi nzuri.

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Nini maktaba CS50? Yeah. >> [Mwanafunzi] Ni kuweka kabla ya kuandikwa ya maadili [inaudible]

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Okay, nzuri.

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Ni kuweka kabla ya kuandikwa ya kificho kwamba sisi wafanyakazi aliandika, sisi kutoa na wewe,

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ambayo hutoa baadhi funktionalitet ya kawaida,

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stuff kama kupata yangu kamba, kupata yangu int - yote ya kazi ambayo ni waliotajwa hapa.

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

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Sisi ni kwenda kuanza kuchukua string kutoka kwenu,

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ambayo wanakumbuka mara tu kisawe kwa ajili ya aina yale halisi data? >> [Nyingi wanafunzi] Char *.

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Char *. Kwa wazazi, kwamba pengine alikuwa [hufanya whooshing sauti]. Hiyo ni nzuri.

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Char * tutaweza kuanza kuona kwenye screen wote zaidi kama sisi kuondoa string 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 kiasi

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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 katika, 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,

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baadhi tovuti mahali fulani.

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>> Basi hebu peel nyuma safu hii kwa mara ya kwanza na kuvuta Appliance CS50

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na faili hii inaitwa cs50.h, ambayo tumekuwa # ikiwa ni pamoja na kwa wiki,

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lakini hebu kweli kuona nini ndani ya hii.

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juu ya faili katika bluu ni tu rundo zima la comments:

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udhamini habari na leseni.

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Hii ni aina ya dhana ya kawaida katika programu

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kwa sababu mengi ya programu siku hizi ni nini wito chanzo wazi,

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ambayo ina maana kwamba mtu ameandika code na alifanya hivyo kwa uhuru zaidi

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si tu kukimbia na kutumia 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, 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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Ilani ya juu hapa kwamba faili cs50.h ni pamoja na rundo zima la files header.

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Wengi wa haya, sisi hawajaona mbele, lakini moja ni familiar.

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Kati ya hao kuwa sisi kuonekana, angalau kwa ufupi, hivi sasa? >> [Mwanafunzi] darasa la maktaba.

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Yeah, kiwango maktaba. stdlib.h ina malloc.

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Mara sisi kuanza kuzungumza juu ya mgao wa nguvu ya 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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Sisi kwa wiki wamekuwa pamoja stdbool.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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Kama sisi kitabu chini zaidi, hapa ni ufafanuzi yetu ya kamba.

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

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Unaweza hata kuwa na nafasi pande zote.

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Sisi huu muhula wamekuwa kukuza kama hii kufanya wazi

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kwamba nyota ina nini na aina,

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lakini kutambua tu kama kawaida, kama siyo kidogo zaidi ya kawaida,

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ni kuweka huko, lakini functionally ni kitu kimoja.

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Lakini sasa kama sisi kusoma chini zaidi, hebu tuangalie GetInt

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kwa sababu sisi kutumika kwamba labda kwanza kabla ya kitu kingine chochote hii muhula.

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Hapa ni GetInt. Hii ni nini? >> [Mwanafunzi] mfano. >> Hii ni mfano.

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Mara nyingi, sisi kuweka prototypes katika vilele vya wetu c files.,

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lakini unaweza pia kuweka prototypes katika files header,. h files, kama hii moja hapa

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hivyo kwamba wakati wewe kuandika baadhi ya majukumu ya kwamba unataka watu wengine kuwa na uwezo wa kutumia,

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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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Kisha kwamba faili header ni nini marafiki na wafanyakazi wenzake ni pamoja na

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na # 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 #,

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ambayo kimsingi nakala na pastes faili hii katika yako mwenyewe.

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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 fulani.

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Nini kama mtumiaji aina katika idadi hiyo ni njia kubwa mno, quintillion,

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kwamba tu hawezi fit ndani ya int? Je, ni tabia yanayotarajiwa?

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Kimsingi, ni kutabirika.

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Hivyo katika kesi hii, kama kweli kusoma magazeti faini,

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utasikia kweli kuona kwamba kama mstari hauwezi kusoma, hii INT_MAX atakaporudi.

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Sisi sijawahi kuongelea kuhusu hili, lakini kwa kuzingatia mtaji wake, ni nini pengine?

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[Mwanafunzi] mara kwa mara. >> Ni mara kwa mara.

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Ni baadhi ya mara kwa mara maalum kwamba pengine alitangaza katika moja ya files wale header

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kwamba ni juu ya juu katika faili, na INT_MAX pengine ni kitu kama takribani 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: -2 bilioni 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 -2000000000,

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hivyo unaweza kutumia moja ya maadili yako iwezekanavyo ili uweze kufanya kwa dunia

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

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Lakini hutaki mtumiaji kuandika kitu kama cryptic 234 ..., idadi kubwa kweli kweli.

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Wewe generalize badala kama mara kwa mara.

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Hivyo kweli, kama wewe walikuwa kuwa anal majuma machache yaliyopita, wakati wowote wewe kuitwa GetInt,

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unapaswa kuangalia kwa kuwa kama hali alifanya aina user katika INT_MAX,

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au, hasa zaidi, alifanya GetInt kurudi INT_MAX, kwa sababu kama ni hivyo,

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kwamba kwa kweli ina maana hawakuwa aina yake. Kitu potoka katika kesi hii.

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

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>> Hebu sasa kurejea katika faili c..

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Faili C limekuwepo katika appliance kwa muda fulani.

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Na kwa kweli, appliance ina kabla ya compiled kwa wewe ndani ya kwamba kitu 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 ambapo ni: appliance.

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Hebu kitabu chini sasa kwa GetInt na kuona jinsi GetInt imekuwa ikifanya kazi muda wote huu.

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Hapa tuna sawa maoni kutoka kabla.

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Hebu kuvuta tu sehemu code.

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Na nini sisi kwa GetInt ni zifuatazo.

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Inachukua hakuna pembejeo.

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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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>> Hebu angalia jinsi hii matendo.

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Tunaonekana kutumia GetString katika mstari huu wa kwanza ndani ya kitanzi, 166.

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Hii sasa ni mazoezi mazuri kwa sababu chini ya mazingira gani inaweza GetString kurudi

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maalum Keyword null? >> [Mwanafunzi] Kama kitu fulani kitaenda vibaya.

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Kama kitu fulani kitaenda vibaya. Na nini inaweza kwenda vibaya wakati wewe piga kitu kama GetString?

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Yeah. >> [Mwanafunzi] Malloc inashindwa kuwapa ints.

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Yeah. Labda malloc inashindwa.

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Mahali fulani chini ya Hood, GetString wito malloc, ambao unagawa kumbukumbu,

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ambayo inakuwezesha kuhifadhi kompyuta zote za wahusika

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kwamba mtumiaji aina katika keyboard.

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Na kudhani mtumiaji alikuwa na mengi nzima ya muda bure na typed zaidi, kwa mfano,

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kuliko bilioni 2 wahusika katika, wahusika zaidi ya kompyuta hata ina RAM.

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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 namna fulani kuwa na uwezo wa kushughulikia suala hili,

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na hivyo GetString, kama sisi akaenda nyuma na kusoma nyaraka zake, anafanya katika ukweli null kurudi.

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Hivyo sasa ikiwa GetString inashindwa na kurudi null, GetInt ataenda kushindwa na kurudi INT_MAX

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tu kama sentinel. Hizi ni baadhi tu ya binadamu makongamano.

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njia pekee ya kujua hii ni kesi ni kwa kusoma nyaraka.

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>> Hebu kitabu chini ambapo int ni kweli waliopata.

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

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Tunatangaza katika 172 int, n, na Char, c, na kisha kazi hii mpya,

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ambayo baadhi yenu mashaka hela kabla, sscanf.

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Hii anasimama kwa scanf kamba.

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

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Hiyo ina maana gani?

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Tuseme kwamba ninapoandika katika, literally, 123 katika keyboard na kisha hit kuingia.

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Je, ni aina ya data ya 123 wakati akarudi na GetString? >> [Mwanafunzi] Kamba.

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Ni wazi kamba, sawa? I got kamba.

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Hivyo 123 ni kweli, quote-unquote, 123 na 0 \ katika mwisho wake.

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Hiyo siyo int. Hiyo si idadi. Inaonekana kama idadi lakini si kweli.

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Hiyo ni nini GetInt kufanya?

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Ina Scan kwamba string kushoto kwenda kulia - 123 \ 0 - na kwa namna fulani kubadilisha na integer halisi.

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Unaweza kufikiri jinsi ya kufanya hili.

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Kama unafikiri nyuma pset2, wewe labda got kidogo starehe na Kaisari

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au Vigenere, hivyo unaweza iterate juu ya kamba, unaweza kubadilisha chars kwa ints.

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Lakini heck, 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, unatarajia nini kuona katika kamba hii.

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Na 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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Na zinageuka kuwa nukuu hii sasa ni kukumbusha ya stuff tulipoanza kuzungumza kuhusu

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tu zaidi ya wiki iliyopita.

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Nini ni & n na & c kufanya kwa sisi hapa? >> [Mwanafunzi] mitaani ya n na anuani ya c.

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Yeah. Ni kunipa anuani ya n na anuani ya c. Kwa nini ni kwamba ni muhimu?

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Unajua kwamba pamoja na utendaji katika C, unaweza daima kurudi thamani au hakuna thamani wakati wote.

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Unaweza kurudi int, kamba, kuelea, char, chochote, au unaweza kurudi batili,

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lakini unaweza tu kurudi jambo moja Upeo.

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Lakini hapa tunataka sscanf kurudi kwangu labda int, idadi decimal,

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na pia Char, na mimi itabidi kueleza kwa nini Char katika wakati huu.

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Wewe unataka ufanisi sscanf kurudi mambo mawili, lakini kwamba si tu inawezekana katika C.

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Unaweza kufanya kazi ya kuzunguka kwamba kwa kupita katika anwani mbili

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kwa sababu kwa haraka kama wewe mkono kazi anwani mbili,

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nini wanaweza kufanya kazi hiyo pamoja nao? >> [Mwanafunzi] Andika anwani hizo.

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Ni unaweza kuandika kwa anwani hizo.

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Unaweza kutumia operesheni nyota na kwenda huko, kwa kila moja ya anwani hizo.

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Ni aina ya mfumo huu nyuma-mlango lakini kawaida sana kwa ajili ya kubadilisha maadili ya vigezo

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zaidi ya moja tu mahali - katika kesi hii, mbili.

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Sasa mimi nina taarifa ya kuangalia kwa == 1 na kisha kurudi n kama hana, kwa kweli, kutathmini kwa kweli.

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Basi nini kinaendelea? Kitaalam, wote kweli tunataka kutokea katika GetInt ni hii.

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Tunataka kuchanganua, ili kuzungumza, tunataka kusoma string - quote-unquote 123 -

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na kama inaonekana kama kuna idadi huko, nini tuko kuwaambia sscanf kufanya

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ni kuweka kwamba idadi - 123 - katika hili variable n kwa ajili yangu.

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Hivyo kwa nini basi, mimi kwa kweli kuwa na hili pia?

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Ni nini nafasi ya sscanf akisema unaweza pia kupata tabia hapa?

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[Inaudible mwanafunzi majibu] >> uhakika decimal kweli anaweza kufanya kazi.

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Hebu kushikilia kwamba walidhani kwa muda. Gani kingine?

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[Mwanafunzi] Ni inaweza kuwa null. >> Bora mawazo. Ni inaweza kuwa tabia null.

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Ni kweli si katika kesi hii. Yeah. >> [Mwanafunzi] ASCII.

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ASCII. Au ngoja generalize hata zaidi.

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C% kuna tu kwa ajili ya kuangalia makosa.

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Hatutaki kuwa kuna tabia baada ya idadi,

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lakini nini hii inaruhusu mimi kufanya ni yafuatayo.

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Ni zinageuka kuwa sscanf, badala ya kuhifadhi maadili katika n na c katika mfano huu hapa,

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nini pia haina ni kuirudisha idadi ya vigezo ni kuweka maadili in

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00:19:24,890 --> 00:19:30,260
Hivyo kama wewe tu aina katika 123, basi tu d% ni kwenda mechi,

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na tu n anapata kuhifadhiwa kwa thamani kama 123,

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na hakuna kitu anapata kuweka katika c.

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C bado thamani ya takataka, hivyo kusema -

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takataka kwa sababu ni haijawahi initialized kwa thamani fulani.

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Hivyo katika kesi hiyo, sscanf anarudi 1 kwa sababu mimi wakazi 1 ya kuyatumia hizo,

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katika kesi ambayo kubwa, nina int hivyo mimi huru line ya bure juu ya kumbukumbu

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GetString kwamba kweli zilizotengwa, na kisha mimi kurudi n,

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mwingine kama wewe umewahi kujiuliza ambapo kwamba Jaribu tena kauli huja kutoka, inakuja kutoka kulia hapa.

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Hivyo kama, kwa kulinganisha, ninapoandika katika 123foo - baadhi tu mlolongo random ya asilia -

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sscanf ni kwenda kuona idadi, hesabu, idadi, f,

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na ni kwenda kuweka 123 katika n; ni kwenda kuweka f katika c na kisha kurudi 2.

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Hivyo tuna, tu kutumia ufafanuzi wa msingi wa tabia ya sscanf, njia rahisi sana -

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vizuri, tata katika mtazamo wa kwanza lakini mwisho wa siku haki rahisi utaratibu -

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ya kusema ni kuna int na kama ni hivyo, ni kwamba kitu pekee mimi kupatikana?

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Na hapa ni whitespace makusudi.

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Kama unaweza kusoma nyaraka kwa ajili ya sscanf, ni anakwambia kwamba kama wewe ni pamoja na kipande ya whitespace

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mwanzoni au mwishoni, sscanf pia itaruhusu mtumiaji, kwa sababu yoyote,

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hit nafasi bar 123 na kwamba itakuwa ya halali.

340
00:20:41,860 --> 00:20:44,150
Huwezi yell katika user tu kwa sababu wao hit nafasi bar

341
00:20:44,150 --> 00:20:48,640
mwanzoni au mwishoni, ambayo ni kidogo tu zaidi user-kirafiki.

342
00:20:48,640 --> 00:20:52,300
>> Maswali yoyote juu ya basi GetInt? Yeah. >> [Mwanafunzi] Je, iwapo tu ya kuweka katika Char?

343
00:20:52,300 --> 00:20:54,030
Nzuri swali.

344
00:20:54,030 --> 00:20:59,890
Je, iwapo tu typed katika Char kama f na hit Enter bila hata kuandika 123?

345
00:20:59,890 --> 00:21:02,420
Unafikiri hii tabia ya mstari wa kanuni basi ingekuwa?

346
00:21:02,420 --> 00:21:04,730
[Inaudible mwanafunzi majibu]

347
00:21:04,730 --> 00:21:08,790
Yeah, hivyo sscanf unaweza cover kwamba pia kwa sababu katika kesi hiyo, siyo kwenda kujaza n au c.

348
00:21:08,790 --> 00:21:15,310
Ni kwenda badala kurudi 0, katika kesi ambayo mimi nina pia kuambukizwa kwamba tukio

349
00:21:15,310 --> 00:21:18,750
kwa sababu thamani inatarajiwa nataka ni 1.

350
00:21:18,750 --> 00:21:22,000
Mimi nataka tu moja na jambo moja tu ya kujazwa. Nzuri swali.

351
00:21:22,000 --> 00:21:24,290
>> Wengine? Wote haki.

352
00:21:24,290 --> 00:21:26,250
>> Hebu si kwenda kwa yote ya kazi katika hapa,

353
00:21:26,250 --> 00:21:29,500
lakini moja ambayo inaonekana kuwa labda ya riba iliyobaki ni GetString

354
00:21:29,500 --> 00:21:32,790
kwa sababu ni zinageuka kuwa GetFloat, GetInt, GetDouble, GetLongLong

355
00:21:32,790 --> 00:21:36,260
wote punt mengi ya utendaji wao wa GetString.

356
00:21:36,260 --> 00:21:39,750
Basi hebu tuangalie jinsi yeye ni kutekelezwa hapa.

357
00:21:39,750 --> 00:21:43,630
Hii moja inaonekana tata kidogo, lakini hutumia misingi sawa

358
00:21:43,630 --> 00:21:45,670
kwamba sisi kuanza kuzungumza kuhusu wiki iliyopita.

359
00:21:45,670 --> 00:21:49,490
Katika GetString, ambayo inachukua hakuna hoja kama kwa utupu juu hapa

360
00:21:49,490 --> 00:21:53,730
na kuirudisha kamba, mimi inaonekana ni kutangaza string kuitwa buffer.

361
00:21:53,730 --> 00:21:56,270
Mimi kwa kweli sijui ni nini ambayo inaenda kutumika kwa ajili bado, lakini tutaweza kuona.

362
00:21:56,270 --> 00:21:58,390
Inaonekana kama uwezo ni kwa default 0.

363
00:21:58,390 --> 00:22:01,350
Uhakika kabisa ambapo hii ni kwenda, uhakika nini n inaenda kutumika kwa ajili bado,

364
00:22:01,350 --> 00:22:03,590
lakini sasa ni kupata zaidi kidogo ya kuvutia.

365
00:22:03,590 --> 00:22:06,520
Katika mstari 243, sisi kutangaza int, c.

366
00:22:06,520 --> 00:22:08,800
Hii ni aina ya kina ya kijinga.

367
00:22:08,800 --> 00:22:15,820
Char ni 8 bits, na 8 bits unaweza kuhifadhi wangapi maadili tofauti? >> [Mwanafunzi] 256. >> 256.

368
00:22:15,820 --> 00:22:20,730
Tatizo ni kama unataka kuwa na 256 tofauti wahusika ASCII, ambayo kuna

369
00:22:20,730 --> 00:22:23,340
kama unafikiri nyuma - na hii si kitu kwa kukariri.

370
00:22:23,340 --> 00:22:25,710
Lakini kama unadhani nyuma chati kwamba kubwa ASCII tulikuwa wiki iliyopita,

371
00:22:25,710 --> 00:22:30,600
kulikuwa katika kesi hiyo 128 au 256 wahusika ASCII.

372
00:22:30,600 --> 00:22:32,940
Sisi kutumika mifumo yote ya hadi sekunde 0 na 1s.

373
00:22:32,940 --> 00:22:36,210
Hiyo ni tatizo kama unataka kuwa na uwezo wa kuchunguza makosa

374
00:22:36,210 --> 00:22:40,190
kwa sababu kama uko tayari kutumia maadili 256 kwa wahusika wako,

375
00:22:40,190 --> 00:22:43,050
wewe si kweli mpango wa mbele kwa sababu sasa una hakuna njia ya kusema,

376
00:22:43,050 --> 00:22:46,270
hii si tabia ya legit, hii ni baadhi ya ujumbe makosa.

377
00:22:46,270 --> 00:22:50,270
Basi nini dunia gani ni wao kutumia ijayo kubwa thamani, kitu kama int,

378
00:22:50,270 --> 00:22:54,720
ili kuwa na idadi ya mambo bits, 32, kwa ajili ya maadili bilioni 4 iwezekanavyo

379
00:22:54,720 --> 00:22:58,860
hivyo kwamba unaweza tu kuishia kutumia kimsingi 257 kati yao,

380
00:22:58,860 --> 00:23:01,720
1 ya ambayo ina baadhi maana maalum kama makosa.

381
00:23:01,720 --> 00:23:03,120
>> Basi hebu angalia jinsi hii matendo.

382
00:23:03,120 --> 00:23:07,760
Katika mstari 246, nina hii kubwa wakati kitanzi kwamba ni wito fgetc,

383
00:23:07,760 --> 00:23:11,090
f maana ya SVG, hivyo getc, na kisha stdin.

384
00:23:11,090 --> 00:23:15,520
Ni zinageuka hii ni njia tu sahihi zaidi ya kusema kusoma pembejeo kutoka keyboard.

385
00:23:15,520 --> 00:23:19,300
Darasa la pembejeo njia keyboard, pato kiwango ina maana screen,

386
00:23:19,300 --> 00:23:23,310
na kiwango makosa, ambayo tutaweza kuona katika pset4, ina maana screen

387
00:23:23,310 --> 00:23:27,490
lakini sehemu maalum ya screen ili siyo alikataa na pato halisi

388
00:23:27,490 --> 00:23:30,750
kwamba lengo na magazeti. Lakini zaidi juu ya kwamba katika siku zijazo.

389
00:23:30,750 --> 00:23:34,440
Hivyo fgetc njia tu kusoma moja tabia kutoka keyboard na kuhifadhi wapi?

390
00:23:34,440 --> 00:23:37,350
Kuhifadhi katika c.

391
00:23:37,350 --> 00:23:41,360
Na kisha kuangalia - hivyo mimi nina kutumia tu kuhusianisha baadhi Boolean hapa -

392
00:23:41,360 --> 00:23:46,000
kuangalia kwamba hana sawa - \ n, hivyo user ina hit Enter, tunataka kukomesha katika hatua hiyo,

393
00:23:46,000 --> 00:23:49,850
mwisho wa kitanzi - na sisi pia wanataka kuangalia kwa EOF maalum ya mara kwa mara,

394
00:23:49,850 --> 00:23:53,610
ambayo kama unajua au nadhani, ni nini kusimama kwa? >> [Mwanafunzi] Mwisho wa faili. >> Mwisho wa faili.

395
00:23:53,610 --> 00:23:56,560
Hii ni aina ya kiupuzi kwa sababu kama mimi nina kuandika katika keyboard,

396
00:23:56,560 --> 00:23:58,870
kuna kweli hakuna faili kushiriki katika hili,

397
00:23:58,870 --> 00:24:01,150
lakini hii tu ya aina ya muda generic kutumika kwa maana ya

398
00:24:01,150 --> 00:24:04,220
kwamba kitu kingine ni kuja kutoka kwa vidole binadamu.

399
00:24:04,220 --> 00:24:06,460
EOF - mwisho wa faili.

400
00:24:06,460 --> 00:24:09,920
Kama kando, kama wameweza milele hit Document D saa keyboard yako, si kwamba ungependa kuwa bado -

401
00:24:09,920 --> 00:24:15,230
ve hit Document C - Document D zituma hii mara kwa mara maalum iitwayo EOF.

402
00:24:15,230 --> 00:24:19,850
Hivyo sasa sisi tu baadhi ya nguvu ya kumbukumbu mgao.

403
00:24:19,850 --> 00:24:23,440
>> Hivyo kama (n + 1> uwezo). Sasa mimi itabidi kueleza n.

404
00:24:23,440 --> 00:24:26,100
N ni jinsi tu wengi ka ni sasa katika buffer,

405
00:24:26,100 --> 00:24:28,620
kamba kwamba wewe sasa kujenga kutoka kwa mtumiaji.

406
00:24:28,620 --> 00:24:33,450
Kama una zaidi ya wahusika katika buffer yako kuliko wewe kuwa na uwezo katika buffer,

407
00:24:33,450 --> 00:24:37,410
intuitively nini tunahitaji kufanya basi ni kutenga zaidi ya uwezo.

408
00:24:37,410 --> 00:24:43,330
Hivyo nina kwenda kwa skim juu ya baadhi ya hesabu hapa na lengo tu juu ya kazi hii hapa.

409
00:24:43,330 --> 00:24:46,070
Unajua nini malloc ni au ni angalau ujumla ukoo.

410
00:24:46,070 --> 00:24:48,970
Kuchukua nadhani nini realloc gani. >> [Mwanafunzi] Anaongeza kumbukumbu.

411
00:24:48,970 --> 00:24:52,920
Siyo kabisa kuongeza kumbukumbu. Ni reallocates kumbukumbu kama ifuatavyo.

412
00:24:52,920 --> 00:24:57,220
Kama bado kuna chumba katika mwisho wa kamba kukupa zaidi ya kumbukumbu ya kwamba

413
00:24:57,220 --> 00:25:00,000
kuliko awali inakupa, kisha utapata kwamba kumbukumbu ya ziada.

414
00:25:00,000 --> 00:25:03,460
Hivyo unaweza tu kuendelea kuweka wahusika string wa nyuma kwa nyuma kwa nyuma kwa nyuma.

415
00:25:03,460 --> 00:25:05,830
Lakini kama si kwamba kesi kwa sababu wewe walisubiri muda mrefu sana

416
00:25:05,830 --> 00:25:07,940
na kitu random got plopped katika kumbukumbu kuna

417
00:25:07,940 --> 00:25:10,290
lakini kuna kumbukumbu ya ziada hapa chini, hiyo ni sawa.

418
00:25:10,290 --> 00:25:13,100
Realloc anaenda kufanya kuinua nzito kwa ajili yenu,

419
00:25:13,100 --> 00:25:16,750
hoja string umeisoma katika hivi sasa kutoka hapa, akaiweka chini huko,

420
00:25:16,750 --> 00:25:19,460
na kisha kukupa baadhi zaidi Runway katika hatua hiyo.

421
00:25:19,460 --> 00:25:22,550
>> Hivyo, pamoja na wimbi la mkono, basi mimi kusema kwamba kile GetString ni kufanya

422
00:25:22,550 --> 00:25:26,330
ni ni kwa kuanzia na buffer ndogo, labda moja tabia,

423
00:25:26,330 --> 00:25:30,820
na kama mtumiaji aina katika herufi mbili, GetString kuishia wito realloc na anasema

424
00:25:30,820 --> 00:25:33,150
moja tabia hiyo haitoshi; nipe herufi mbili.

425
00:25:33,150 --> 00:25:35,950
Kisha kama kusoma kwa njia ya mantiki ya kitanzi, ni kwenda kusema

426
00:25:35,950 --> 00:25:39,600
user typed katika herufi 3; nipe sasa si 2 lakini 4 wahusika,

427
00:25:39,600 --> 00:25:42,320
kisha nipe 8, basi nipe 16 na 32.

428
00:25:42,320 --> 00:25:45,000
ukweli kwamba mimi nina uwezo mara dufu kila wakati

429
00:25:45,000 --> 00:25:48,570
ina maana kwamba buffer si kwenda kukua polepole, ni kwenda kukua super kufunga.

430
00:25:48,570 --> 00:25:51,380
Na nini inaweza kuwa faida ya kwamba?

431
00:25:51,380 --> 00:25:54,600
Kwa nini mimi mara mbili ya ukubwa wa buffer

432
00:25:54,600 --> 00:25:58,020
hata kama mtumiaji ili tu haja moja ya ziada tabia kutoka keyboard?

433
00:25:58,020 --> 00:26:01,750
[Inaudible mwanafunzi majibu] >> gani hiyo? >> [Mwanafunzi] Huna kukua ni kama mara nyingi.

434
00:26:01,750 --> 00:26:03,300
Hasa. Huna kukua ni kama mara nyingi.

435
00:26:03,300 --> 00:26:05,510
Na hii ni aina tu ya wewe ni Hedging bets yako hapa,

436
00:26:05,510 --> 00:26:10,850
wazo kuwa kuwa hutaki kuwaita realloc mengi kwa sababu huelekea kuwa polepole.

437
00:26:10,850 --> 00:26:12,910
Wakati wowote kuuliza mfumo wa uendeshaji kwa ajili ya kumbukumbu,

438
00:26:12,910 --> 00:26:16,990
kama wewe utakuwa haraka kuona katika kuweka baadaye tatizo, huelekea kuchukua muda.

439
00:26:16,990 --> 00:26:20,010
Hivyo kukanusha kwamba kiasi cha muda, hata kama wewe ni kupoteza baadhi ya nafasi,

440
00:26:20,010 --> 00:26:21,900
huelekea kuwa ni jambo jema.

441
00:26:21,900 --> 00:26:24,060
>> Lakini kama sisi kusoma kupitia sehemu ya mwisho ya GetString hapa -

442
00:26:24,060 --> 00:26:27,950
na tena kuelewa kila line moja hapa sio muhimu leo ​​-

443
00:26:27,950 --> 00:26:30,530
taarifa kwamba hatimaye wito malloc tena

444
00:26:30,530 --> 00:26:33,880
na kutenga hasa kama ka wengi kama ni mahitaji kwa kamba

445
00:26:33,880 --> 00:26:38,060
na kisha throws mbali na wito bure buffer kupita kiasi kikubwa

446
00:26:38,060 --> 00:26:40,080
kama ni kweli got mara mbili mara nyingi sana.

447
00:26:40,080 --> 00:26:42,730
Hivyo katika muda mfupi, kwamba ni jinsi GetString imekuwa ikifanya kazi muda wote huu.

448
00:26:42,730 --> 00:26:47,060
Yote gani ni kusoma moja ya tabia kwa wakati tena na tena na tena,

449
00:26:47,060 --> 00:26:50,750
na kila wakati inahitaji baadhi ya kumbukumbu ya ziada, inauliza mfumo wa uendeshaji kwa

450
00:26:50,750 --> 00:26:53,670
kwa kumwita realloc.

451
00:26:53,670 --> 00:26:57,890
>> Maswali yoyote? Wote haki.

452
00:26:57,890 --> 00:26:59,270
>> mashambulizi.

453
00:26:59,270 --> 00:27:04,060
Sasa kwa kuwa tunaelewa kuyatumia au angalau zinazidi ukoo na kuyatumia,

454
00:27:04,060 --> 00:27:06,700
hebu fikiria jinsi dunia zima kuanza kuanguka

455
00:27:06,700 --> 00:27:10,030
kama huna kabisa kulinda dhidi ya watumiaji adversarial,

456
00:27:10,030 --> 00:27:11,850
watu ambao ni kujaribu Hack ndani ya mfumo wako,

457
00:27:11,850 --> 00:27:16,890
watu ambao ni kujaribu kuiba programu yako kwa circumventing baadhi ya kanuni za usajili

458
00:27:16,890 --> 00:27:19,090
wapate kuwa vinginevyo na aina in

459
00:27:19,090 --> 00:27:22,990
>> Kuangalia mfano huu hapa, ambayo ni tu C kificho kwamba ina kazi kuu chini

460
00:27:22,990 --> 00:27:26,380
kwamba wito foo kazi. Na kile ni kupitisha foo?

461
00:27:26,380 --> 00:27:29,680
[Mwanafunzi] hoja moja. >> [Malan] hoja moja.

462
00:27:29,680 --> 00:27:33,450
Hivyo argv [1], ambayo ina maana ya neno kwanza kwamba mtumiaji typed katika mstari amri

463
00:27:33,450 --> 00:27:36,360
baada a.out au chochote mpango inaitwa.

464
00:27:36,360 --> 00:27:41,680
Hivyo foo juu inachukua katika * Char. Lakini * Char ni yale tu? >> [Mwanafunzi] kamba.

465
00:27:41,680 --> 00:27:43,350
[Malan] kamba, hivyo kuna kitu kipya hapa.

466
00:27:43,350 --> 00:27:45,420
Hiyo kamba ni kiholela kuitwa bar.

467
00:27:45,420 --> 00:27:51,430
Katika mstari huu hapa, char c [12]; katika aina ya nusu ya kiufundi Kiingereza, ni nini mstari huu kufanya?

468
00:27:51,430 --> 00:27:55,220
[Mwanafunzi] safu ya - >> Array ya? >> [Mwanafunzi] Nyingine. >> Nyingine.

469
00:27:55,220 --> 00:27:58,870
Nipe safu ya wahusika 12. Hivyo tupate wito huu buffer.

470
00:27:58,870 --> 00:28:02,920
Ni kitaalam inaitwa c, lakini buffer katika programu njia tu rundo la nafasi

471
00:28:02,920 --> 00:28:04,800
kuwa unaweza kuweka baadhi ya mambo in

472
00:28:04,800 --> 00:28:07,940
Kisha mwisho, memcpy tumekuwa si kutumika kabla, lakini pengine unaweza nadhani nini inakuwa hivyo.

473
00:28:07,940 --> 00:28:10,480
Ni nakala ya kumbukumbu. Ni nini nini?

474
00:28:10,480 --> 00:28:19,270
Ni dhahiri nakala bar, mchango wake, katika c lakini tu hadi urefu wa bar.

475
00:28:19,270 --> 00:28:24,930
Lakini kuna mdudu hapa. >> [Mwanafunzi] Unahitaji tabia sizeof. >> Sawa.

476
00:28:24,930 --> 00:28:30,860
Kitaalam, tunatakiwa kufanya strlen (bar) * sizeof (Char)). Hiyo ni sahihi.

477
00:28:30,860 --> 00:28:33,930
Lakini katika hali mbaya hapa, hebu kudhani kwamba that's -

478
00:28:33,930 --> 00:28:35,950
Sawa. Kisha kuna mbili mende.

479
00:28:35,950 --> 00:28:39,160
Hivyo sizeof (Char));

480
00:28:39,160 --> 00:28:41,290
Hebu tufanye hili kidogo pana.

481
00:28:41,290 --> 00:28:44,910
Hivyo sasa bado kuna mdudu, ambayo ni nini? >> [Inaudible mwanafunzi majibu]

482
00:28:44,910 --> 00:28:46,990
Angalia kwa nini? >> [Mwanafunzi] Angalia kwa null.

483
00:28:46,990 --> 00:28:50,270
Tunapaswa ujumla kuangalia kwa null sababu mambo mabaya kutokea

484
00:28:50,270 --> 00:28:53,200
wakati pointer yako ni null sababu unaweza kuishia kwenda huko,

485
00:28:53,200 --> 00:28:57,630
na unapaswa si milele kuwa kwenda kwa null na dereferencing kwa operator nyota.

486
00:28:57,630 --> 00:29:01,050
Basi hiyo ni nzuri. Na kile kingine ni sisi kufanya? Kimantiki, kuna flaw hapa pia.

487
00:29:01,050 --> 00:29:04,450
[Mwanafunzi] Angalia kama argc ni> = kwa 2.

488
00:29:04,450 --> 00:29:10,550
Ili kuangalia kama ni argc> = 2. Okay, hivyo kuna tatu mende katika mpango huu hapa.

489
00:29:10,550 --> 00:29:16,630
Sisi ni sasa kuangalia kama mtumiaji kweli typed katika kitu chochote ndani ya argv [1]. Nzuri.

490
00:29:16,630 --> 00:29:20,950
Basi nini mdudu wa tatu? Yeah. >> [Mwanafunzi] C wanaweza kuwa kubwa ya kutosha.

491
00:29:20,950 --> 00:29:23,320
Nzuri. Sisi checked moja tukio.

492
00:29:23,320 --> 00:29:29,520
Sisi implicitly checked usinakili zaidi kuliko kumbukumbu ingekuwa kisichozidi urefu wa bar.

493
00:29:29,520 --> 00:29:32,510
Hivyo kama string mtumiaji typed katika ni 10 wahusika muda mrefu,

494
00:29:32,510 --> 00:29:36,020
hii ni kusema tu nakala wahusika 10. Na hiyo ni sawa.

495
00:29:36,020 --> 00:29:39,940
Lakini nini kama mtumiaji typed katika neno saa haraka kama neno 20-tabia?

496
00:29:39,940 --> 00:29:44,900
Hii ni kusema nakala wahusika 20 kutoka bar ndani ya nini?

497
00:29:44,900 --> 00:29:49,750
C, inayojulikana kama buffer yetu, ambayo ina maana tu aliandika data

498
00:29:49,750 --> 00:29:52,540
hadi 8 Byte maeneo ambayo huna mwenyewe,

499
00:29:52,540 --> 00:29:54,870
na humiliki yao kwa maana ya kwamba kamwe zilizotengwa kwao.

500
00:29:54,870 --> 00:30:00,370
Hivyo hii ni nini ujumla inayojulikana kama mashambulizi buffer kufurika au buffer mashambulizi overrun.

501
00:30:00,370 --> 00:30:05,580
Na ni mashambulizi kwa maana kwamba kama mtumiaji au programu hiyo ni wito kazi yako

502
00:30:05,580 --> 00:30:10,490
ni kufanya hivyo kwa nia mbaya, nini hasa kinatokea ijayo inaweza kweli kabisa mbaya.

503
00:30:10,490 --> 00:30:12,450
>> Basi hebu tuangalie picha hii hapa.

504
00:30:12,450 --> 00:30:16,060
Hii picha inawakilisha stack yako ya kumbukumbu.

505
00:30:16,060 --> 00:30:19,580
Kumbuka kwamba kila wakati wewe piga kazi kupata sura hii kidogo juu ya stack

506
00:30:19,580 --> 00:30:21,520
na kisha mwingine na kisha mwingine na mwingine.

507
00:30:21,520 --> 00:30:24,300
Na hivi sasa, tumekuwa aina tu ya abstracted haya kama mistatili

508
00:30:24,300 --> 00:30:26,290
aidha ubaoni au kwenye screen hapa.

509
00:30:26,290 --> 00:30:30,580
Lakini kama sisi zoom katika kwenye moja ya mistatiri hizo, wakati wewe piga foo kazi,

510
00:30:30,580 --> 00:30:35,880
zinageuka kuwa kuna zaidi juu ya ndani ya stack ya frame kwamba katika mstatili kwamba

511
00:30:35,880 --> 00:30:40,060
kuliko tu x na y na a na b, kama sisi hawakuwa kuzungumza juu ya kubadilishana.

512
00:30:40,060 --> 00:30:44,410
Ni zinageuka kuwa kuna baadhi ya maelezo ya chini ya ngazi, kati yao Kurudi mitaani.

513
00:30:44,410 --> 00:30:49,550
Hivyo zinageuka wakati kuu wito foo, kuu ina kuwajulisha foo

514
00:30:49,550 --> 00:30:53,520
nini anwani kuu ni katika kumbukumbu ya kompyuta

515
00:30:53,520 --> 00:30:57,770
kwa sababu vinginevyo, kwa haraka kama foo inafanywa utekelezaji, kama katika kesi hii hapa,

516
00:30:57,770 --> 00:31:00,830
mara moja wewe kufikia hii funge curly brace mwishoni mwa foo,

517
00:31:00,830 --> 00:31:05,310
jinsi heck haina foo kujua ambapo udhibiti wa mpango zinatakiwa kwenda?

518
00:31:05,310 --> 00:31:08,970
Ni zinageuka kuwa jibu la swali hilo ni katika mstatili hii nyekundu hapa.

519
00:31:08,970 --> 00:31:12,670
Hii inawakilisha pointer, na ni juu ya kompyuta kuhifadhi kwa muda

520
00:31:12,670 --> 00:31:17,030
juu ya stack kinachojulikana anuani ya kuu ili haraka kama foo inafanywa utekelezaji,

521
00:31:17,030 --> 00:31:21,120
kompyuta anajua wapi na nini line katika kuu ya kwenda nyuma ya.

522
00:31:21,120 --> 00:31:23,940
Kuokolewa Frame pointer inahusiana vile vile kwa hii.

523
00:31:23,940 --> 00:31:26,310
Char * bar hapa inawakilisha nini?

524
00:31:26,310 --> 00:31:31,350
Sasa hii sehemu ya bluu hapa ni sura ya foo. Je, ni bar?

525
00:31:31,570 --> 00:31:35,010
Bar ni tu hoja kwa kazi foo.

526
00:31:35,010 --> 00:31:37,500
Hivyo sasa tuko nyuma katika aina ya picha za ukoo.

527
00:31:37,500 --> 00:31:39,850
Kuna zaidi ya mambo na distractions zaidi juu ya screen,

528
00:31:39,850 --> 00:31:43,380
lakini hii mwanga sehemu bluu tu ni nini tumekuwa kuchora ubaoni

529
00:31:43,380 --> 00:31:45,790
kwa kitu kama byta. Hiyo ni sura kwa foo.

530
00:31:45,790 --> 00:31:51,490
Na kitu pekee katika haki sasa ni bar, ambayo ni hii parameter.

531
00:31:51,490 --> 00:31:55,220
Lakini nini kingine unapaswa kuwa katika stack kulingana na kanuni hii hapa?

532
00:31:55,220 --> 00:31:57,760
[Mwanafunzi] Char c [12]. >> [Malan] Char c [12].

533
00:31:57,760 --> 00:32:02,810
Tunapaswa pia kuona viwanja 12 ya kumbukumbu zilizotengwa kwa ajili ya variable kuitwa c,

534
00:32:02,810 --> 00:32:04,970
na kwa kweli hatuwezi kuwa na kwamba kwenye screen.

535
00:32:04,970 --> 00:32:08,480
sana juu kuna c [0], na kisha mwandishi wa mchoro huu

536
00:32:08,480 --> 00:32:11,850
haikujali kuchora wote wa mraba, lakini kuna shaka 12 kuna

537
00:32:11,850 --> 00:32:16,590
kwa sababu kama ukiangalia chini kulia, c [11] kama wewe kuhesabu kutoka 0 12 ni vile Byte.

538
00:32:16,590 --> 00:32:18,400
Lakini hapa ni tatizo.

539
00:32:18,400 --> 00:32:22,390
Ambayo mwelekeo ni kuongezeka c?

540
00:32:22,390 --> 00:32:27,080
Aina ya juu chini ikiwa ni kuanza saa ya juu na kukua hadi chini.

541
00:32:27,080 --> 00:32:30,110
Haionekani kama sisi kushoto wenyewe Runway sana hapa wakati wote.

542
00:32:30,110 --> 00:32:32,090
Tumekuwa aina ya walijenga wenyewe ndani ya kona,

543
00:32:32,090 --> 00:32:36,940
na kwamba c [11] ni haki juu ya bar, ambayo ni haki ya juu dhidi ya pointer Saved Frame,

544
00:32:36,940 --> 00:32:39,960
ambayo ni haki juu ya mitaani Kurudi. Hakuna chumba zaidi.

545
00:32:39,960 --> 00:32:42,810
Basi nini maana basi kama wewe screw up

546
00:32:42,810 --> 00:32:46,500
na wewe jaribu kusoma ka 20 ndani ya buffer 12-Byte?

547
00:32:46,500 --> 00:32:50,060
Ambapo ni wale 8 ka ziada kwenda? >> [Mwanafunzi] Ndani -

548
00:32:50,060 --> 00:32:53,200
Ndani ya kila kitu kingine, ambayo baadhi ni super muhimu.

549
00:32:53,200 --> 00:32:57,260
Na jambo muhimu zaidi, uwezekano, ni sanduku nyekundu huko, Kurudi mitaani,

550
00:32:57,260 --> 00:33:03,560
kwa sababu tuchukulie kwamba wewe ama ajali au adversarially overwrite ka wale 4,

551
00:33:03,560 --> 00:33:07,260
kwamba anuani pointer, si tu kwa takataka lakini kwa idadi

552
00:33:07,260 --> 00:33:09,810
kinachotokea kwa kuwakilisha anuani halisi katika kumbukumbu.

553
00:33:09,810 --> 00:33:13,880
Nini maana, mantiki? >> [Mwanafunzi] Kazi ni kwenda kuwarudisha mahali tofauti.

554
00:33:13,880 --> 00:33:15,250
Hasa.

555
00:33:15,250 --> 00:33:19,170
Wakati foo anarudi na hits kwamba brace curly, mpango ni kwenda kuendelea

556
00:33:19,170 --> 00:33:25,060
wasimrudie kuu, ni kwenda na kurudi kwa chochote anuani ni katika sanduku kwamba nyekundu.

557
00:33:25,060 --> 00:33:28,600
>> Katika kesi ya usajili circumventing programu,

558
00:33:28,600 --> 00:33:32,260
nini kama anuani hiyo kuwa alirejea ni kazi ambayo kwa kawaida anapata kuitwa

559
00:33:32,260 --> 00:33:35,690
baada ve kulipwa kwa ajili ya programu na inputted usajili wako code?

560
00:33:35,690 --> 00:33:39,870
Unaweza aina ya hila ya kompyuta katika si kwenda hapa lakini badala yake kwenda hapa.

561
00:33:39,870 --> 00:33:45,100
Au kama wewe ni kweli wajanja, adui unaweza kweli aina katika saa keyboard, kwa mfano,

562
00:33:45,100 --> 00:33:50,690
si neno halisi, wahusika si 20, lakini nadhani yeye au yeye kweli aina katika

563
00:33:50,690 --> 00:33:52,770
baadhi ya wahusika kwamba kuwakilisha code.

564
00:33:52,770 --> 00:33:55,320
Na si kwenda kuwa C kificho, ni kweli kwenda kuwa wahusika

565
00:33:55,320 --> 00:33:59,290
kwamba kuwakilisha binary mashine code, sekunde 0 na 1s.

566
00:33:59,290 --> 00:34:01,290
Lakini tuseme wao uko wajanja kutosha kufanya hivyo,

567
00:34:01,290 --> 00:34:06,500
kwa namna fulani kuweka katika kitu GetString haraka ambayo kimsingi ni compiled kificho,

568
00:34:06,500 --> 00:34:09,980
na mwisho 4 ka overwrite kwamba anuani kurudi.

569
00:34:09,980 --> 00:34:13,360
Na nini anwani haina pembejeo kwamba kufanya?

570
00:34:13,360 --> 00:34:18,630
Ni kweli katika maduka ya Mstatili hii nyekundu anuani ya Byte kwanza ya buffer.

571
00:34:18,630 --> 00:34:23,070
Hivyo wewe kuwa kweli wajanja, na hii ni mengi ya kesi na makosa kwa watu mbaya huko nje,

572
00:34:23,070 --> 00:34:25,639
lakini kama unaweza kufikiri ni jinsi gani kubwa buffer hii ni

573
00:34:25,639 --> 00:34:28,820
vile kwamba mwisho ka chache katika pembejeo, kutoa kwa mpango

574
00:34:28,820 --> 00:34:33,540
kutokea kwa kuwa sawa na anuani ya mwanzo wa buffer yako, unaweza kufanya hivyo.

575
00:34:33,540 --> 00:34:39,320
Tukisema kawaida hujambo na \ 0, kwamba ni nini mwisho juu katika buffer.

576
00:34:39,320 --> 00:34:44,420
Lakini kama tupo zaidi wajanja na sisi kujaza kwamba buffer na kile tutaweza generically kuwaita mashambulizi code -

577
00:34:44,420 --> 00:34:48,860
AAA, mashambulizi, mashambulizi, mashambulizi - ambapo hii ni tu kitu ambacho hana kitu mbaya,

578
00:34:48,860 --> 00:34:51,820
kile kinachotokea kama wewe ni kweli wajanja, unaweza kufanya kazi hii.

579
00:34:51,820 --> 00:34:58,610
Katika sanduku nyekundu hapa ni mlolongo wa idadi - 80, C0, 35, 08.

580
00:34:58,610 --> 00:35:01,610
Ona kwamba kuwa mechi ya idadi hiyo ni hapa juu.

581
00:35:01,610 --> 00:35:04,430
Ni katika utaratibu reverse, lakini zaidi juu ya wakati kwamba baadhi nyingine.

582
00:35:04,430 --> 00:35:08,140
Ona kwamba anuani hii kurudi imekuwa makusudi ilibadilika

583
00:35:08,140 --> 00:35:12,020
kwa anuani sawa hapa, si anuani ya kuu.

584
00:35:12,020 --> 00:35:17,500
Hivyo kama mtu mbaya ni super smart, yeye au yeye ni kwenda kwa pamoja katika kificho kwamba mashambulizi

585
00:35:17,500 --> 00:35:20,930
kitu kama kufuta wote wa files mtumiaji au kunakili nywila

586
00:35:20,930 --> 00:35:24,680
au kuunda akaunti ya mtumiaji kwamba naweza kisha kuingia kwenye - chochote wakati wote.

587
00:35:24,680 --> 00:35:26,950
>> Na hii ni hatari zote na nguvu ya C.

588
00:35:26,950 --> 00:35:29,840
Kwa sababu unaweza kupata kumbukumbu kupitia kuyatumia

589
00:35:29,840 --> 00:35:32,520
na kwa hiyo unaweza kuandika kitu chochote unataka ndani ya kumbukumbu ya kompyuta,

590
00:35:32,520 --> 00:35:35,080
unaweza kufanya kompyuta kufanya kitu chochote unataka

591
00:35:35,080 --> 00:35:39,550
tu na baada yake kuruka karibu ndani ya nafasi yake mwenyewe kumbukumbu.

592
00:35:39,550 --> 00:35:44,650
Na hivyo kwa siku hii ya mipango mingi na tovuti nyingi kwamba ni kuathirika

593
00:35:44,650 --> 00:35:46,200
chemsha chini ya watu kuchukua faida ya hii.

594
00:35:46,200 --> 00:35:50,760
Na hii inaweza kuonekana kama mashambulizi super kisasa, lakini haina daima kuanza kwa njia hiyo.

595
00:35:50,760 --> 00:35:53,560
ukweli ni kwamba watu wabaya itakuwa kawaida kufanya ni,

596
00:35:53,560 --> 00:35:58,200
kama ni mpango katika mstari amri au mpango GUI au tovuti,

597
00:35:58,200 --> 00:35:59,940
wewe tu kuanza kutoa nonsense.

598
00:35:59,940 --> 00:36:03,980
Wewe aina katika neno kubwa kweli kweli ndani ya shamba tafuta na hit Enter,

599
00:36:03,980 --> 00:36:05,780
na wewe kusubiri kuona kama tovuti shambulio

600
00:36:05,780 --> 00:36:09,990
au wewe kusubiri kuona kama mpango hudhihirisha baadhi ujumbe wa makosa

601
00:36:09,990 --> 00:36:14,330
kwa sababu kama wewe kupata bahati kama mtu mbaya na wewe kutoa baadhi ya pembejeo mambo

602
00:36:14,330 --> 00:36:18,980
kwamba shambulio mpango, kwamba maana ya programu Hawakutarajia tabia yako mbaya,

603
00:36:18,980 --> 00:36:23,630
ambayo ina maana unaweza pengine kwa juhudi za kutosha, kesi ya kutosha na makosa,

604
00:36:23,630 --> 00:36:26,650
kufikiri jinsi ya kupigana mashambulizi sahihi zaidi.

605
00:36:26,650 --> 00:36:31,410
Hivyo kama sehemu kubwa ya usalama si tu kuepuka mashambulizi haya kabisa

606
00:36:31,410 --> 00:36:34,100
lakini kuchunguza yao na kwa kweli kuangalia magogo

607
00:36:34,100 --> 00:36:36,780
na kuona nini pembejeo mambo kuwa watu typed katika tovuti yako,

608
00:36:36,780 --> 00:36:38,960
nini tafuta masharti kuwa watu typed katika tovuti yako

609
00:36:38,960 --> 00:36:42,870
kwa matumaini ya kufurika baadhi buffer.

610
00:36:42,870 --> 00:36:45,500
Na hii yote majipu chini misingi rahisi ya nini safu

611
00:36:45,500 --> 00:36:49,080
na nini maana ya kutenga na kutumia kumbukumbu.

612
00:36:49,080 --> 00:36:51,710
>> Kuhusiana na kwamba basi pia ni hii.

613
00:36:51,710 --> 00:36:54,280
Hebu tu mtazamo ndani ya gari ngumu bado tena.

614
00:36:54,280 --> 00:36:58,440
Unakumbuka kutoka wiki moja au mbili zilizopita kwamba wakati wewe Drag files yako kusaga bin au takataka unaweza,

615
00:36:58,440 --> 00:37:03,710
nini kinatokea? >> [Mwanafunzi] Hakuna. >> Kabisa kitu, sawa?

616
00:37:03,710 --> 00:37:05,740
Hatimaye kama wewe kukimbia chini juu ya nafasi disk,

617
00:37:05,740 --> 00:37:08,190
Windows au Mac OS itaanza kufuta faili kwa ajili yenu.

618
00:37:08,190 --> 00:37:10,390
Lakini kama wewe Drag kitu huko, kwamba si wote salama.

619
00:37:10,390 --> 00:37:13,800
Zote roommate yako au rafiki au familia ina kufanya ni bonyeza mara mbili na, voilà,

620
00:37:13,800 --> 00:37:16,310
kuna mafaili yote sketchy kwamba alijaribu kufuta.

621
00:37:16,310 --> 00:37:19,590
Wengi wetu angalau kujua kwamba una haki bonyeza au Udhibiti click

622
00:37:19,590 --> 00:37:22,310
na tupu takataka au kitu kama hicho.

623
00:37:22,310 --> 00:37:25,000
Lakini hata hivyo haina kabisa kufanya hila

624
00:37:25,000 --> 00:37:28,010
kwa sababu kile kinachotokea wakati una faili kwenye gari yako ngumu

625
00:37:28,010 --> 00:37:32,770
kwamba inawakilisha baadhi ya hati Neno au baadhi JPEG, na hii inawakilisha gari yako ngumu,

626
00:37:32,770 --> 00:37:35,350
na hebu sema hii Sliver hapa inawakilisha kwamba faili,

627
00:37:35,350 --> 00:37:38,390
na ni linajumuisha rundo zima la sekunde 0 na 1s.

628
00:37:38,390 --> 00:37:42,470
Nini kinatokea wakati wewe si tu Drag kwamba faili kwa takataka wanaweza au kusaga bin

629
00:37:42,470 --> 00:37:48,020
lakini pia ni tupu? Aina ya kitu.

630
00:37:48,020 --> 00:37:49,640
Ni si kitu kabisa sasa.

631
00:37:49,640 --> 00:37:54,290
Sasa ni kitu tu kwa sababu kitu kidogo kinachotokea katika fomu ya meza hii.

632
00:37:54,290 --> 00:37:58,370
Hivyo kuna baadhi ya aina ya database au meza ndani ya kumbukumbu ya kompyuta

633
00:37:58,370 --> 00:38:03,850
kwamba kimsingi ina moja kwa safu files 'majina na moja kwa safu files' mahali,

634
00:38:03,850 --> 00:38:07,720
ambapo hii inaweza kuwa mahali 123, tu idadi random.

635
00:38:07,720 --> 00:38:14,560
Hivyo sisi tupate kuwa na kitu kama x.jpeg na mahali 123.

636
00:38:14,560 --> 00:38:18,800
Kinachotokea baadae wakati kwa kweli tupu takataka yako?

637
00:38:18,800 --> 00:38:20,330
Kwamba huenda mbali.

638
00:38:20,330 --> 00:38:23,610
Lakini ni nini si kwenda mbali ni sekunde 0 na 1s.

639
00:38:23,610 --> 00:38:26,270
>> Basi nini basi uhusiano na pset4?

640
00:38:26,270 --> 00:38:31,240
Naam, na pset4, kwa sababu tu tumekuwa ajali erased kompakt flash kadi

641
00:38:31,240 --> 00:38:35,750
kwamba alikuwa zote za picha hizi au tu kwa sababu ni kwa bahati mbaya akawa kupotoshwa

642
00:38:35,750 --> 00:38:38,000
haina maana kwamba sekunde 0 na 1s si bado kuna.

643
00:38:38,000 --> 00:38:40,410
Labda wachache wao ni kupotea kwa sababu kitu got kupotoshwa

644
00:38:40,410 --> 00:38:43,320
kwa maana kwamba sekunde 0 baadhi akawa 1s na 1s akawa sekunde 0.

645
00:38:43,320 --> 00:38:47,240
Mambo mabaya yanaweza kutokea kwa sababu ya programu Buggy au defective vifaa.

646
00:38:47,240 --> 00:38:50,370
Lakini wengi wa bits wale, labda hata 100% ya nao, bado kuna.

647
00:38:50,370 --> 00:38:55,050
Ni tu kwamba kompyuta au kamera hajui ambapo JPEG1 ilianza

648
00:38:55,050 --> 00:38:56,910
na ambapo JPEG2 kuanza.

649
00:38:56,910 --> 00:39:01,070
Lakini kama wewe, programu, kujua na kidogo ya savvy ambapo wale JPEGs ni

650
00:39:01,070 --> 00:39:06,010
au nini wao kuangalia kama hivyo unaweza kuchambua JPEG sekunde 0 na 1s na kusema, JPEG,

651
00:39:06,010 --> 00:39:09,440
unaweza kuandika mpango na kimsingi tu kwa wakati au kitanzi

652
00:39:09,440 --> 00:39:12,820
kwamba recovers kila mmoja files wale.

653
00:39:12,820 --> 00:39:16,030
Hivyo basi ni somo kuanza salama erasing files yako

654
00:39:16,030 --> 00:39:18,340
kama Ningependa ili kuepuka hili kabisa. Ndiyo.

655
00:39:18,340 --> 00:39:21,010
>> [Mwanafunzi] Jinsi kuja anasema juu ya kompyuta yako

656
00:39:21,010 --> 00:39:23,550
kwamba una kumbukumbu zaidi kuliko alivyofanya kabla?

657
00:39:23,550 --> 00:39:27,820
Kuwa na zaidi ya kumbukumbu ya wewe alifanya mbele - >> [mwanafunzi] Zaidi inapatikana kumbukumbu.

658
00:39:27,820 --> 00:39:29,630
Oh. Nzuri swali.

659
00:39:29,630 --> 00:39:32,360
Hivyo kwa nini basi baada ya kumwaga maji ya takataka haina kompyuta yako kukuambia

660
00:39:32,360 --> 00:39:34,910
kwamba una zaidi bure nafasi kuliko wewe alifanya mbele?

661
00:39:34,910 --> 00:39:36,770
Kwa kifupi, kwa sababu ni uongo.

662
00:39:36,770 --> 00:39:40,740
Zaidi ya kitaalam, una nafasi zaidi kwa sababu sasa umesema

663
00:39:40,740 --> 00:39:43,680
unaweza kuweka mambo mengine ambapo faili kwamba mara moja mara.

664
00:39:43,680 --> 00:39:45,450
Lakini hiyo haina maana bits ni kwenda mbali,

665
00:39:45,450 --> 00:39:48,590
na hiyo haina maana bits ni kuwa iliyopita kwa sekunde 0 wote, kwa mfano,

666
00:39:48,590 --> 00:39:50,150
kwa kinga yako.

667
00:39:50,150 --> 00:39:54,640
Hivyo kwa kulinganisha, kama wewe salama erase files au kimwili kuharibu kifaa,

668
00:39:54,640 --> 00:39:57,300
kwamba kweli ni njia pekee wakati mwingine kuzunguka kwamba.

669
00:39:57,300 --> 00:40:02,020
>> Hivyo kwa nini sisi kuondoka kwamba kumbuka nusu inatisha, na sisi kuona juu ya Jumatatu.

670
00:40:02,020 --> 00:40:07,000
[Applause]

671
00:40:07,780 --> 00:40:10,000
>> [CS50.TV]