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[Powered by Google Translate] [Valgrind]

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[Nate Hardison, Università ta 'Harvard]

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Dan huwa CS50, CS50.TV]

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Uħud mill-bugs aktar diffiċli fil-programmi C

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ġejjin mill-ġestjoni ħażina tal-memorja.

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Hemm numru kbir ta 'modi biex screw affarijiet up,

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inkluż allokat l-ammont ħażin ta 'memorja,

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jinsa li initialize-varjabbli,

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miktub qabel jew wara t-tmiem ta 'buffer,

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u tillibera jżommu ħinijiet memorja multipli.

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Is-sintomi jvarjaw minn ħabtiet intermittenti

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għall-valuri mysteriously miktub fuq xulxin,

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spiss fil-postijiet u l-ħinijiet bogħod mill-iżball oriġinali.

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Tracing-problema osservata lura lill-għerq sottostanti

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jista 'jkun sfida,

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iżda fortunatament hemm programm utli imsejjaħ Valgrind

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li jistgħu jagħmlu ħafna biex jgħinu.

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>> Inti tmexxi programm taħt Valgrind biex

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verifika estensiva tal-allokazzjonijiet tal-memorja borġ u aċċessi.

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Meta Valgrind jiskopri problema, li tagħtik immedjat,

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informazzjoni diretta li jippermetti li inti

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aktar faċilment isibu u tiffissa l-problema.

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Valgrind wkoll rapporti dwar kwistjonijiet memorja inqas fatali,

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bħal tnixxijiet memorja, l-allokazzjoni tal-memorja borġ,

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u jinsa biex ħielsa minnha.

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Bħal kompilatur, tagħna clang, fil-debugger tagħna, GDB,

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Valgrind huwa softwer b'xejn, u huwa installat fuq il-appliance.

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Valgrind timxi fuq eżekutibbli binarju tiegħek,

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mhux tiegħek. c jew. fajls kodiċi h sors,

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sabiex ikun żgur li għandek miġbura kopja up-to-data tal-programm tiegħek

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użu clang jew Għamla.

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Imbagħad, ġiri program tiegħek taħt Valgrind jista 'jkun

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sempliċi kemm biss prefiss-kmand programm standard bl-Valgrind kelma,

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li jibda up Valgrind u jmexxi l-programm ġewwa ta 'dan.

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Meta jibdew, Valgrind ma xi kumpless

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jiggering biex jiġi kkonfigurat l-eżekutibbli għall-kontrolli tal-memorja,

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sabiex ikun jista 'jieħu ftit biex tikseb jibda jaħdem.

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Il-programm għandu mbagħad tesegwixxi normalment, ikun ferm aktar bil-mod,

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u meta jispiċċa, Valgrind se print sommarju ta 'użu tal-memorja tiegħu.

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Jekk kollox imur sew, se tfittex xi ħaġa bħal din:

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F'dan il-każ,. / Clean_program

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hija t-triq għall-programm Irrid jiddekorri.

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U filwaqt li dan wieħed ma jagħmel ebda argumenti,

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jekk hija ma I d biss tindi minnhom fuq sat-tmiem tal-kmand bħas-soltu.

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Programm Nadif huwa biss programm ftit iblah I maħluqa

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li jalloka spazju għal blokk ta 'ints fuq il-munzell,

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tpoġġi xi valuri ġewwa minnhom, u jillibera l-blokk kollu.

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Dan huwa dak li qed shooting għal, l-ebda żbalji u l-ebda tnixxijiet.

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>> Ieħor metrika importanti huwa n-numru totali ta 'bytes allokati.

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Jiddependi fuq il-programm, jekk allokazzjonijiet tiegħek huma fil-megabytes jew ogħla,

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int probabilment tagħmel xi ħaġa ħażina.

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Inti bla bżonn ħażna duplikati?

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Inti tuża l-borġ għall-ħażna, meta ikun aħjar li tuża l-munzell?

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Allura, żbalji memorja jista 'jkun verament ħażen.

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Dawk l-aktar evidenti jikkawżaw ħabtiet spettakolari,

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iżda anki allura xorta tista 'tkun diffiċli biex jiġu identifikati

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x'inhi eżattament wassal għall-tiġrifa.

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Aktar insidjuż, programm bi żball memorja

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xorta jistgħu jikkompilaw nadif

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u xorta jistgħu jidhru li qed jaħdmu b'mod korrett

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għaliex inti irnexxielhom jiksbu xortik tajba ħafna mill-ħin.

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Wara diversi "riżultati ta 'suċċess,"

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inti tista 'biss taħseb li crash huwa fluke tal-kompjuter,

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iżda l-kompjuter huwa qatt żbaljata.

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>> Running Valgrind jistgħu jgħinuk jillokalizzaw l-kawża ta 'żbalji memorja viżibbli

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kif ukoll isibu lurking żbalji inti lanqas biss għadhom jafu dwar.

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Kull darba Valgrind jiskopri problema, stampi informazzjoni dwar dak li osservat.

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Kull oġġett huwa pjuttost konċiż -

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il-linja sors ta 'l-istruzzjoni toffendi, dak il-kwistjoni hija,

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u info ftit dwar il-memorja involuti -

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iżda ħafna drabi huwa biżżejjed informazzjoni sabiex jidderieġu l-attenzjoni tiegħek għall-post dritt.

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Hawn hu eżempju ta 'Valgrind taħdem fuq programm Buggy

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li ma li taqra invalidu 'memorja borġ.

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Naraw l-ebda żbalji jew twissijiet fil-kompilazzjoni.

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Uh-oh, is-sommarju iżball jgħid li hemm żewġ żbalji -

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2 jaqra invalidi ta 'daqs 4 - bytes, li hu.

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Kemm ħażin jaqra seħħew fil-funzjoni prinċipali invalid_read.c,

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l-ewwel fuq il-linja 16 u t-tieni fuq il-linja 19.

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Ejja nħarsu lejn il-kodiċi.

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Id-Dehra tal-ewwel sejħa għall printf tipprova jinqraw wieħed int passat l-aħħar ta 'blokka tal-memorja tagħna.

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Jekk inħarsu lura lejn produzzjoni Valgrind s,

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naraw li Valgrind qalulna eżattament dan.

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L-indirizz aħna qed jippruvaw biex taqra jibda 0 bytes

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passat il-tarf tal-blokka ta 'daqs 16 bytes -

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4 32-bit ints li aħna allokati.

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Dan huwa, l-indirizz konna tipprova taqra jibda dritt fl-aħħar ta 'blokk tagħna,

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biss kif naraw fis-sejħa printf tagħna ħżiena.

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Issa, invalidu jaqra jista 'ma tidhirx bħal li kbar ta' ftehim,

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imma jekk inti qed tuża din id-data biex jikkontrolla l-fluss tal-programm tiegħek -

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per eżempju, bħala parti minn jekk id-dikjarazzjoni jew loop -

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allura l-affarijiet jistgħu imorru ħażin skiet.

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Watch kif I tista 'tmexxi l-programm invalid_read

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u xejn barra min-normal jiġri.

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Scary, huh?

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>> Issa, ejja nħarsu lejn uħud tipi aktar ta 'żbalji li inti tista' tiltaqa fil-kodiċi tiegħek,

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u aħna ser tara kif Valgrind jiskopri minnhom.

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Aħna biss raw eżempju ta 'invalid_read,

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hekk issa ejja check out invalid_write.

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Għal darb'oħra, l-ebda żbalji jew twissijiet fil-kompilazzjoni.

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Okay, Valgrind jgħid li hemm żewġ żbalji f'dan il-programm -

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u invalid_write u invalid_read.

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Ejja check out din il-kodiċi.

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Id-Dehra konna ltqajna każ ta 'l-strlen klassika u wieħed bug.

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Il-kodiċi ma malloc byte żejda ta 'l-ispazju

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għall-karattru / 0,

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hekk meta str kopja marru jiktbu dan fil ssubstrlen "cs50 blat!"

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hija kitbet 1 byte passat il-tarf tal-blokka tagħna.

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Il invalid_read ġejja meta nagħmlu sejħa tagħna għal printf.

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Printf jispiċċa qari memorja invalidu meta jaqra l / 0 karattru

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kif jidher fl-aħħar ta 'dan sekwenza E huwa l-istampar.

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Imma xejn minn dan maħruba Valgrind.

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Naraw li qabad il-invalid_write bħala parti mill-kopja str

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fuq il-linja 11 tat ewlenija, u l-invalid_read hija parti mill printf.

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Rock fuq, Valgrind.

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Għal darb'oħra, dan ma jista 'jidher bħala big deal.

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Aħna tista 'taħdem dan il-programm fuq u aktar barra tal Valgrind

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u ma tara l-ebda sintomi ta 'żball.

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>> Madankollu, ejja nħarsu lejn varjazzjoni żgħira ta 'dan biex tara

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kif l-affarijiet jistgħu jiksbu verament ħżiena.

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Għalhekk, mogħtija, aħna qed jabbużaw affarijiet aktar minn sempliċiment daqsxejn f'dan il-kodiċi.

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Aħna biss allokazzjoni ta 'spazju fuq il-borġ għal żewġ kordi

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it-tul ta 'cs50 blat,

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din id-darba, ftakar l / 0 karattru.

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Imma allura aħna tarmi string super-twil fil-blokk memorja

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li S hija li tipponta lejn.

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X'effett se jkollu dan fuq il-blokka tal-memorja li l-punti T sa?

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Ukoll, jekk il-punti T għal memorja li jinsab biss maġenb S,

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ġejjin biss wara dan,

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allura aħna jista 'jkollha miktub fuq parti ta' T.

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Ejja run dan il-kodiċi.

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Ħares lejn dak li ġara.

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Il-kordi aħna maħżuna fi blokki munzell tagħna kemm dehret li stampati b'mod korrett.

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Xejn jidher ħażin fil-livelli kollha.

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Madankollu, ejja mmorru lura fis-kodiċi tagħna u

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jikkummentaw l-linja fejn aħna kopja cs50 blat

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fil-blokk memorja 2, innotat mill-t.

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Issa, meta aħna run dan il-kodiċi għandna

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biss tara l-kontenut tal-blokka tal-memorja 1 jistampa.

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Whoa, anke jekk aħna ma str kopja

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xi karattri ġewwa l-blokk munzell 2, l-1 indikat mill T,

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irridu jiksbu print out.

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Tabilħaqq, l-sekwenza aħna mimli fis ewwel blokk tagħna

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skorriet l-ewwel blokk u fil-blokk 2,

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jagħmlu kollox jidher normali.

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Valgrind, għalkemm, jgħidilna l-istorja vera.

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Hemm immorru.

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Kollha ta 'dawk invalidi jaqra u jikteb.

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>> Ejja nħarsu lejn eżempju ta 'tip ieħor ta' żball.

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Hawnhekk aħna nagħmlu xi ħaġa pjuttost sfortunati.

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Aħna grab spazju għal int fuq il-munzell,

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u aħna initialize l pointer int - p - għall-punt li dak l-ispazju.

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Madankollu, filwaqt li pointer tagħna huwa initialized,

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id-data li huwa tipponta lejn ftit ikun x'ikun junk huwa fil-parti tal-borġ.

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Allura meta aħna tagħbija li d-data fis INT i,

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aħna teknikament initialize i,

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iżda nagħmlu hekk ma 'data junk.

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Is-sejħa li jasserixxu, li huwa makro debugging handy

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definit fil-adattat issemmiet tasserixxi librerija,

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se abort-programm jekk il-kundizzjoni tat-test tagħha jonqos.

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Dan huwa, jekk i ma tkunx 0.

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Jiddependi fuq dak li kien fl-ispazju borġ, innotat mill p,

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dan il-programm jista 'jaħdem kultant u jonqsu f'ħinijiet oħra.

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Jekk din taħdem, aħna qed biss jkollna xxurtjati.

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Il-kompilatur mhux se jaqbdu dan l-iżball, imma Valgrind rieda żgur.

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Hemm naraw l-iżball li jirriżulta mill-użu tagħna ta 'dik id-data junk.

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>> Meta inti jallokaw memorja borġ iżda ma deallocate dan jew ħielsa it-

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li tissejjaħ nixxija.

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Għal żgħir, ħajja qasira programm li tmexxi u immedjatament ħruġ,

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tnixxijiet huma pjuttost ma jagħmlux ħsara,

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iżda għal proġett ta 'daqs akbar u / jew lonġevità,

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anke tnixxija żgħira tista kompost fis xi ħaġa kbira.

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Għal CS50, aħna ma jistennew li inti

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jieħdu ħsieb ta 'ħelsien kollha tal-memorja borġ li inti jallokaw,

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peress li aħna rridu li inti tibni il-ħiliet biex jimmaniġġjaw sew l-proċess manwali

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meħtieġa minn C.

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Biex tagħmel dan, il-programm tiegħek għandu jkollhom eżatta

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one-to-one korrispondenza bejn malloc u sejħiet b'xejn.

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Fortunatament, Valgrind jistgħu jgħinuk ma 'tnixxijiet memorja wisq.

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Hawnhekk huwa programm leaky imsejjaħ leak.c li jalloka

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ispazju fuq il-munzell, jikteb lilu, iżda ma ħielsa minnha.

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Aħna jikkompilaw bl Għamla u run taħt Valgrind,

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u naraw li, filwaqt li aħna għandna l-iżbalji memorja ebda,

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aħna għandna waħda nixxija.

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Hemm 16 bytes definittivament mitlufa,

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li jfisser li l-pointer għal dak memorja ma kienx fl-ambitu tiegħu meta l-programm ħareġ.

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Issa, Valgrind ma tagħtina ton ta 'informazzjoni dwar il-tnixxija,

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imma jekk aħna isegwu din in-nota ftit li tagħti l isfel lejn il-qiegħ tar-rapport tagħha

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li terġa 'ssir bl - leak-check = full

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biex tara d-dettalji sħaħ ta 'memorja nixxew,

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aħna ser tikseb aktar informazzjoni.

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Issa, fis-sommarju munzell,

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Valgrind tgħidilna meta l-memorja li kien mitluf kien inizjalment allokati.

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Just kif nafu minn tfittex fil-kodiċi tas-sors,

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Valgrind tinforma lilna li aħna nixxew l-memorja

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allokat ma 'sejħa għall malloc fuq il-linja 8 tal leak.c

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fil-funzjoni ewlenija.

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Pretty nifty.

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>> Valgrind categorizes tnixxijiet jużaw dawn it-termini:

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Żgur mitlufa - dan huwa borġ memorja allokat

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li l-programm ma għadx għandha pointer.

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Valgrind jaf li inti darba kellhom l-pointer iżda peress tilef rekord ta 'dan.

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Din il-memorja huwa definittivament nixxew.

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Indirettament mitlufa - dan huwa borġ memorja allokat

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li għalihom il-pointers biss għal wkoll huma mitlufa.

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Per eżempju, jekk int mitluf pointer tiegħek għall-node 1 ta 'lista marbuta,

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allura l-node 1 nnifisha tkun definittivament mitlufa,

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filwaqt li xi lymph sussegwenti tkun indirettament mitlufa.

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Possibilment mitlufa - dan huwa borġ memorja allokat

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li Valgrind ma jistax ikun ċert jekk hemmx pointer jew le.

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Still jista 'jintlaħaq huwa borġ memorja allokat

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li l-programm għad għandha pointer fuq ħruġ,

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li tipikament ifisser li l-punti varjabbli globali lilha.

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Biex tiċċekkja għal dawn tnixxijiet, tkun taf ukoll biex jinkludu l-għażla

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- Għadu-jista 'jintlaħaq = iva

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fil invokazzjoni tiegħek ta 'Valgrind.

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>> Dawn il-każijiet differenti jistgħu jeħtieġu strateġiji differenti għat-tindif up,

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iżda tnixxijiet għandhom jiġu eliminati.

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Sfortunatament, l-iffissar tnixxijiet jista 'jkun diffiċli li tagħmel,

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ladarba telefonati mhux korretti għall ħielsa tista 'blow up program tiegħek.

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Per eżempju, jekk inħarsu lejn invalid_free.c,

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naraw eżempju ta deallocation memorja ħażina.

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X'għandu jkun hemm sejħa waħda biex ħielsa l-blokk kollu

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tal-memorja indikat mill int_block,

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Minflok sar tentattiv biex ħielsa kull sezzjoni int 'daqs medju

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tal-memorja individwalment.

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Dan se jonqsu katastrofiku.

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Boom! Liema żball.

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Dan huwa definittivament mhux tajba.

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Jekk int mwaħħla ma 'dan it-tip ta' żball, għalkemm, u ma tafx fejn tfittex,

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jaqgħu lura fuq l-aqwa ħabib tiegħek ġodda.

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Qtajt - Valgrind.

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Valgrind, bħal dejjem, ikun jaf eżattament x'hemm up.

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L-għadd ALLOC u ħielsa ma jaqblu.

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Imxejna ltqajna 1 alloc u 4 jillibera.

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U Valgrind wkoll tgħidilna meta l-ewwel sejħa ħielsa ħażina -

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il-wieħed li wassal għall-blowup - ikun ġej minn -

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linja 16.

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Kif qed taraw, sejħiet ħżiena biex ħielsa huma tassew ħżiena,

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hekk aħna nirrakkomandaw kiri nixxija program tiegħek

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waqt li qed jaħdmu fuq jkollna l-funzjonalità korretta.

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Tibda tfittex għal tnixxijiet biss wara program tiegħek qed jaħdem kif suppost,

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mingħajr l-ebda żbalji oħra.

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>> U li kollox konna ltqajna għal dan il-video.

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Issa dak li huma inti tistenna?

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Mur jimxu Valgrind fuq programmi tiegħek dritt issa.

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Jisimni Nate Hardison. Dan huwa CS50. [CS50.TV]