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[Powered by Google Translate] [Valgrind]

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[Nate Hardison, Chuo Kikuu cha Harvard]

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Hii ni CS50, CS50.TV]

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Baadhi ya mende ngumu zaidi katika mipango ya C

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kuja kutoka usimamiaji mbovu wa kumbukumbu.

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Kuna idadi kubwa ya njia ya kufaidika mambo up,

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ikiwa ni pamoja na kugawa kiasi ya makosa ya kumbukumbu,

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kusahau initialize vigezo,

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kuandika kabla au baada ya mwisho wa buffer,

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na kumkomboa kutunza kumbukumbu mara nyingi.

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dalili mbalimbali kutoka shambulio vipindi

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kwa maadili ya mysteriously overwritten,

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mara nyingi katika sehemu na nyakati mbali kuondolewa kutoka katika makosa ya awali.

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Hazieleweki tatizo aliona nyuma sababu ya msingi mzizi

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inaweza kuwa changamoto,

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lakini bahati nzuri kuna mpango kusaidia aitwaye Valgrind

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ambayo inaweza kufanya mengi kusaidia.

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>> Wewe kukimbia chini ya mpango Valgrind ili kuwawezesha

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kina kuangalia ya mgao wa kumbukumbu chungu na wanapata.

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Wakati Valgrind hutambua tatizo, anakupa haraka,

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moja kwa moja habari kwamba utapata

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zaidi kupata urahisi na kurekebisha tatizo.

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Valgrind pia taarifa juu ya masuala ya chini mauti kumbukumbu,

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kama vile kumbukumbu uvujaji, kugawa lundo kumbukumbu,

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na kusahau ya bure yake.

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Kama compiler yetu, Clang, katika debugger yetu, GDB,

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Valgrind ni programu za bure, na ni imewekwa kwenye appliance.

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Valgrind anaendesha binary executable yako,

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si yako c. au. files chanzo h kificho,

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hivyo kuwa na uhakika kuwa compiled nakala up-to-date ya mpango wako

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kutumia Clang au kufanya.

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Kisha, mbio programu yako chini ya Valgrind inaweza kuwa

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rahisi kama tu prefixing kiwango mpango amri na Valgrind neno,

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ambayo kuanza juu Valgrind na anaendesha programu ndani yake.

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Wakati wa kuanza, Valgrind gani baadhi tata

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jiggering configure executable kwa hundi kumbukumbu,

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hivyo inaweza kuchukua kidogo kuamka na kukimbia.

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Mpango huo basi nitafanya kawaida, kuwa ni taratibu zaidi,

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na wakati atamaliza, Valgrind itakuwa magazeti muhtasari wa kumbukumbu matumizi yake.

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Kama yote inakwenda vizuri, itakuwa kuangalia kitu kama hii:

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Katika kesi hii, /. Clean_program

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ni njia ya mpango nataka kukimbia.

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Na wakati mmoja hii haina kuchukua hoja yoyote,

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kama alivyofanya mimi d tu tack yao ya mwisho wa amri kama kawaida.

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Mpango safi ni tu silly kidogo mpango nilianzisha

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kwamba kutenga nafasi kwa block ya ints juu ya chungu,

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kuweka maadili baadhi ndani yao, na frees block nzima.

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Hii ni nini ni risasi kwa, makosa hakuna uvujaji na hakuna.

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>> Mwingine metric muhimu ni jumla ya idadi ya ka zilizotengwa.

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Kutegemea mpango, kama mgao yako ni katika megabaiti au ya juu,

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pengine wewe kufanya kitu kibaya.

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Je unnecessarily hifadhi marudio?

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Je, unatumia chungu kwa ajili ya kuhifadhi, wakati itakuwa bora kutumia stack?

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Hivyo, kumbukumbu makosa unaweza kuwa kweli maovu.

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ndio zaidi overt kusababisha shambulio kuvutia,

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lakini hata basi bado unaweza kuwa vigumu pinpoint

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nini hasa ulisababisha ajali.

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Zaidi hila na njama zilizotengenezwa, mpango na makosa kumbukumbu

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bado anaweza kukusanya cleanly

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na bado anaweza kuonekana kazi ipasavyo

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kwa sababu wewe imeweza kupata bahati zaidi ya muda.

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Baada ya kadhaa "matokeo ya mafanikio,"

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unaweza tu kufikiri kwamba ajali ni fluke ya kompyuta,

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lakini kompyuta ni kamwe makosa.

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>> Mbio Valgrind inaweza kukusaidia kufuatilia chini sababu ya makosa inayoonekana kumbukumbu

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kama vile kupata lurking makosa huna hata bado kujua juu.

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Kila wakati Valgrind hutambua tatizo, ni Prints taarifa kuhusu ni nini aliona.

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Kila kipengele ni uungwana terse -

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line chanzo cha mafundisho offending, nini suala hilo ni,

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na info kidogo juu ya kumbukumbu wanaohusika -

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lakini mara nyingi ni ya kutosha habari kuelekeza mawazo yako mahali pa haki.

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Hapa ni mfano wa Valgrind mbio juu ya mpango Buggy

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kwamba hana kusoma batili ya kumbukumbu chungu.

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Sisi kuona makosa hakuna maonyo au katika mkusanyiko.

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Uh-oh, muhtasari kosa anasema kuwa kuna makosa mawili -

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mbili batili wasomaji wa kawaida 4 - ka, kwamba ni.

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Wote mbaya anasoma ilitokea katika kazi kuu ya invalid_read.c,

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kwanza katika mstari wa 16 na ya pili juu ya mstari 19.

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Hebu tuangalie code.

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Inaonekana kama ya kwanza mwito kwa printf inajaribu kusoma moja int zamani mwisho wa kumbukumbu block yetu.

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Kama sisi kuangalia nyuma katika pato la Valgrind,

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tunaona kwamba Valgrind alituambia hasa ile.

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anuani ya sisi ni kujaribu kusoma kuanza ka 0

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nyuma mwisho wa block ya kawaida 16 ka -

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nne ya 32-bit ints kwamba sisi zilizotengwa.

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Hiyo ni, anuani tulikuwa kujaribu kusoma kuanza kulia katika mwisho wa kuzuia yetu,

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tu kama sisi kuona katika wito wetu mbaya printf.

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Sasa, batili wasomaji wanaweza kuonekana kama kwamba kubwa ya mpango huo,

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lakini kama wewe ni kutumia data kwamba kudhibiti mtiririko wa mpango wako -

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kwa mfano, kama sehemu ya kama maelezo au kitanzi -

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mambo yanaweza kwenda mbaya kimya.

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Kuangalia jinsi naweza kuendesha programu invalid_read

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na chochote nje ya kawaida hutokea.

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Inatisha, huh?

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>> Sasa, hebu tuangalie baadhi ya aina zaidi ya makosa ambayo unaweza kukutana katika code yako,

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na tutaweza kuona jinsi Valgrind hutambua yao.

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Sisi tu aliona mfano wa invalid_read,

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hivyo sasa hebu angalia invalid_write.

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Tena, hakuna makosa au maonyo katika mkusanyiko.

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Okay, Valgrind anasema kwamba kuna makosa mawili katika mpango huu -

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na invalid_write na invalid_read.

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Hebu angalia hii code.

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Inaonekana kama sisi tumepewa mfano wa strlen classic plus moja mdudu.

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code haina malloc Byte ziada wa nafasi

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kwa tabia / 0,

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hivyo wakati nakala str akaenda kuandika katika ssubstrlen "miamba cs50!"

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ni aliandika 1 Byte zamani mwisho wa kuzuia yetu.

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invalid_read inakuja wakati sisi kufanya wito wetu kwa printf.

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Printf mwisho juu ya kusoma kumbukumbu batili wakati anasoma / 0 tabia

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kama inaonekana katika mwisho wa kamba hii E ni uchapishaji.

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Lakini hakuna hii alitoroka Valgrind.

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Tunaona kwamba hawakupata invalid_write kama sehemu ya nakala str

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kwenye mstari wa 11 kuu, na invalid_read ni sehemu ya printf.

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Rock juu, Valgrind.

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Tena, hii inaweza kuonekana kama mpango kubwa.

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Tunaweza kuendesha programu hii tena na tena nje ya Valgrind

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na wala kuona dalili zozote makosa.

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>> Hata hivyo, hebu angalia tofauti kidogo ya hii kuona

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jinsi mambo wanaweza kupata mbaya kweli kweli.

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Hivyo, nafasi, sisi ni abusing mambo zaidi kuliko kidogo tu katika kanuni hii.

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Sisi ni tu kugawa nafasi kwenye chungu kwa masharti mawili

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urefu wa miamba cs50,

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wakati huu, wakikumbuka / 0 tabia.

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Lakini basi sisi kutupa katika string super-muda mrefu ndani ya kuzuia kumbukumbu

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S ni kwamba akizungumzia.

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Nini athari itakuwa kwamba kuwa juu ya kuzuia kumbukumbu kwamba Simu pointi?

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Naam, kama T pointi kwa kumbukumbu kwamba tu karibu na S,

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kuja tu baada ya hayo,

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kisha sisi tupate kuwa imeandikwa juu ya sehemu ya T.

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Hebu kukimbia hii code.

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Kuangalia nini kilitokea.

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masharti sisi kuhifadhiwa katika vitalu yetu lundo wote alionekana kuwa na kuchapishwa kwa usahihi.

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Hakuna inaonekana vibaya wakati wote.

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Hata hivyo, hebu kwenda nyuma katika kanuni zetu na

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maoni nje mstari ambapo sisi nakala miamba cs50

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katika block pili kumbukumbu, alisema kwa t.

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Sasa, wakati sisi kukimbia hii code tunapaswa

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tu kuona yaliyomo ya kuzuia kwanza kumbukumbu magazeti nje.

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Ho, ingawa hatukuwa str nakala

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yoyote wahusika katika block pili chungu, alisema kwa moja na T,

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sisi kupata magazeti nje.

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Hakika, kamba sisi stuffed katika block wetu wa kwanza

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akaivamia block kwanza na katika block ya pili,

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kufanya kila kitu kuonekana ya kawaida.

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Valgrind, ingawa, inatuambia hadithi ya kweli.

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Kuna sisi kwenda.

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Wote wa wale batili anasoma na anaandika.

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>> Hebu tuangalie mfano wa aina nyingine ya ufisadi.

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Hapa sisi kufanya kitu bahati mbaya.

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Sisi kunyakua nafasi kwa int juu ya chungu,

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na sisi initialize pointer int - p - kwa uhakika na nafasi hiyo.

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Hata hivyo, wakati pointer yetu ni initialized,

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data kwamba ni akizungumzia tu ina chochote Junk ni katika sehemu hiyo ya chungu.

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Hivyo wakati sisi mzigo data kwamba katika int i,

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sisi kitaalam initialize i,

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lakini sisi kufanya hivyo pamoja na data Junk.

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wito kwa kudai, ambayo ni Handy debugging jumla

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inavyoelezwa katika maktaba aptly aitwaye kudai,

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mapenzi abort mpango kama mtihani wake hali inashindwa.

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Hiyo ni, kama i si 0.

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Kutegemea juu ya nini alikuwa katika nafasi chungu, alisema kwa p,

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mpango huu inaweza kufanya kazi wakati mwingine na kushindwa mara kwa mara nyingine.

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Kama ni kazi, sisi ni kupata tu bahati.

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compiler si kukamata kosa hili, lakini Valgrind mapenzi uhakika.

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Kuna sisi kuona makosa yanayotokana na matumizi yetu ya data kwamba Junk.

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>> Wakati wewe kutenga chungu kumbukumbu lakini si deallocate au huru yake,

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kiitwacho leak.

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Kwa wadogo, muda mfupi mpango kwamba anaendesha na mara exits,

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uvujaji ni uungwana wapole,

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lakini kwa ajili ya mradi wa ukubwa kubwa na / au longevity,

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hata leak ndogo inaweza kuzidisha katika kitu makubwa.

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Kwa CS50, hatuwezi kutarajia wewe

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utunzaji wa kumkomboa yote ya kumbukumbu chungu kwamba wewe kutenga,

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tangu tunataka kujenga stadi vizuri kushughulikia mchakato mwongozo

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inavyotakiwa na C.

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Kwa kufanya hivyo, mpango wako awe kamili

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moja kwa moja ya mawasiliano kati ya malloc na wito bure.

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Bahati nzuri, Valgrind inaweza kukusaidia na uvujaji kumbukumbu pia.

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Hapa ni mpango leaky kuitwa leak.c kwamba inatenga

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nafasi kwenye chungu, anaandika kwa hilo, lakini haina huru yake.

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Sisi ni pamoja na kukusanya Matokeo na kukimbia chini ya Valgrind,

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na sisi kuona kwamba, wakati tuna makosa kumbukumbu hakuna,

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sisi kufanya kuwa moja ya uvujaji.

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Kuna 16 ka dhahiri waliopotea,

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maana kwamba pointer kumbukumbu ambayo haikuwa katika wigo wakati mpango exited.

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Sasa, Valgrind hautupatii tani ya taarifa kuhusu leak,

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lakini kama sisi kufuata kumbuka hii kidogo kwamba anatoa chini kuelekea chini ya ripoti yake

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kwa rerun na - leak-kuangalia = kamili

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kuona maelezo kamili ya kumbukumbu kuvuja,

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tutaweza kupata habari zaidi.

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Sasa, katika muhtasari wa chungu,

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Valgrind inatuambia ambapo kumbukumbu aliyepotea awali zilizotengwa.

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Tu kama sisi kujua kutoka kuangalia katika chanzo code,

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Valgrind inatufahamisha ya kwamba sisi kuvuja kumbukumbu

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zilizotengwa kwa mwito wa malloc kwenye mstari 8 ya leak.c

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katika kazi kuu.

197
00:10:00,000 --> 00:10:02,000
Pretty nifty.

198
00:10:02,000 --> 00:10:04,000
>> Valgrind categorizes uvujaji kwa kutumia sheria hizi:

199
00:10:04,000 --> 00:10:07,000
Dhahiri waliopotea - hii ni chungu zilizotengwa kumbukumbu

200
00:10:07,000 --> 00:10:10,000
ambayo mpango tena ina pointer.

201
00:10:10,000 --> 00:10:14,000
Valgrind anajua kwamba wewe mara moja alikuwa pointer lakini tangu waliopotea track yake.

202
00:10:14,000 --> 00:10:17,000
Kumbukumbu hii ni dhahiri kuvuja.

203
00:10:17,000 --> 00:10:20,000
Moja kwa moja walipoteza - hii ni chungu zilizotengwa kumbukumbu

204
00:10:20,000 --> 00:10:24,000
ambayo kuyatumia tu kwa hiyo pia ni kupotea.

205
00:10:24,000 --> 00:10:27,000
Kwa mfano, kama wewe waliopotea pointer yako na nodi ya kwanza ya orodha wanaohusishwa,

206
00:10:27,000 --> 00:10:30,000
kisha nodi kwanza yenyewe itakuwa dhahiri waliopotea,

207
00:10:30,000 --> 00:10:34,000
wakati nodes yoyote baadae itakuwa moja waliopotea.

208
00:10:34,000 --> 00:10:37,000
Uwezekano waliopotea - hii ni chungu zilizotengwa kumbukumbu

209
00:10:37,000 --> 00:10:41,000
ambayo Valgrind haiwezi kuwa na uhakika kama kuna pointer au la.

210
00:10:41,000 --> 00:10:44,000
Bado ni reachable lundo zilizotengwa kumbukumbu

211
00:10:44,000 --> 00:10:47,000
ambayo bado ina mpango pointer katika exit,

212
00:10:47,000 --> 00:10:50,000
ambayo kwa kawaida ina maana kwamba kimataifa variable pointi hiyo.

213
00:10:50,000 --> 00:10:53,000
Ili kuangalia kwa uvujaji hizi, itabidi pia kuwa ni pamoja na chaguo

214
00:10:53,000 --> 00:10:55,000
- Bado-reachable = ndiyo

215
00:10:55,000 --> 00:10:58,000
katika sala yako ya Valgrind.

216
00:10:58,000 --> 00:11:01,000
>> Hizi kesi mbalimbali wanaweza kuhitaji mikakati mbalimbali kwa ajili ya kusafisha yao juu,

217
00:11:01,000 --> 00:11:05,000
lakini uvujaji wanapaswa kuondolewa.

218
00:11:05,000 --> 00:11:08,000
Kwa bahati mbaya, fixing uvujaji inaweza kuwa vigumu kufanya,

219
00:11:08,000 --> 00:11:11,000
tangu sahihi wito kwa bure wanaweza kulipua programu yako.

220
00:11:11,000 --> 00:11:14,000
Kwa mfano, kama sisi kuangalia invalid_free.c,

221
00:11:14,000 --> 00:11:18,000
tunaona mfano wa deallocation mbaya kumbukumbu.

222
00:11:18,000 --> 00:11:21,000
Kile lazima wito moja kwa huru block nzima

223
00:11:21,000 --> 00:11:24,000
ya kumbukumbu alisema kwa int_block,

224
00:11:24,000 --> 00:11:27,000
ina badala kuwa jaribio la kumwondolea kila sehemu int ukubwa

225
00:11:27,000 --> 00:11:29,000
ya kumbukumbu mmoja mmoja.

226
00:11:29,000 --> 00:11:32,000
Hii kushindwa catastrophically.

227
00:11:32,000 --> 00:11:34,000
Boom! Nini kosa.

228
00:11:34,000 --> 00:11:36,000
Hii ni dhahiri si nzuri.

229
00:11:36,000 --> 00:11:39,000
Kama wewe ni kukwama kwa aina hii ya makosa, ingawa, na huwezi kujua wapi kuangalia,

230
00:11:39,000 --> 00:11:41,000
kuanguka nyuma rafiki yako mpya bora.

231
00:11:41,000 --> 00:11:44,000
You guessed it - Valgrind.

232
00:11:44,000 --> 00:11:47,000
Valgrind, kama siku zote, anayejua hasa nini juu.

233
00:11:47,000 --> 00:11:50,000
makosa na alloc bure hayaoani up.

234
00:11:50,000 --> 00:11:52,000
Sisi tumepewa 1 alloc na 4 frees.

235
00:11:52,000 --> 00:11:55,000
Na Valgrind pia inatuambia ambapo kwanza mbaya bure wito -

236
00:11:55,000 --> 00:11:58,000
moja kwamba yalisababisha blowup - anakuja kutoka -

237
00:11:58,000 --> 00:12:00,000
mstari 16.

238
00:12:00,000 --> 00:12:03,000
Kama unaweza kuona, mbaya wito kwa huru ni mbaya kweli kweli,

239
00:12:03,000 --> 00:12:05,000
hivyo sisi kupendekeza kuruhusu mpango wako leak

240
00:12:05,000 --> 00:12:08,000
wakati wewe kazi kupata utendaji sahihi.

241
00:12:08,000 --> 00:12:12,000
Kuanza kuangalia kwa uvujaji tu baada ya mpango wako ni kazi vizuri,

242
00:12:12,000 --> 00:12:14,000
bila makosa yoyote nyingine.

243
00:12:14,000 --> 00:12:16,000
>> Na kwamba wote sisi tumepewa kwa video hii.

244
00:12:16,000 --> 00:12:18,000
Sasa ni wewe kusubiri?

245
00:12:18,000 --> 00:12:21,000
Nenda kukimbia Valgrind juu ya mipango yako sasa hivi.

246
00:12:21,000 --> 00:12:25,000
Jina langu ni Nate Hardison. Hii ni CS50. [CS50.TV]