1 00:00:00,000 --> 00:00:09,780 >> [Music kucheza] 2 00:00:09,780 --> 00:00:11,150 >> ZAMYLA CHAN: Hebu kukabiliana na kupona. 3 00:00:11,150 --> 00:00:14,030 Kuokoa pengine ni pset favorite, na hasa kwa sababu mimi nadhani ni 4 00:00:14,030 --> 00:00:15,650 kweli, kweli baridi. 5 00:00:15,650 --> 00:00:19,040 Kimsingi, wewe ni kupewa kumbukumbu faili kadi ambayo 6 00:00:19,040 --> 00:00:20,900 picha kuwa imefutwa. 7 00:00:20,900 --> 00:00:23,650 Lakini nini ni kwenda kufanya ni kuokoa yao yote. 8 00:00:23,650 --> 00:00:24,250 >> OK. 9 00:00:24,250 --> 00:00:28,230 Hivyo ni kweli kusisimua, lakini labda kidogo vitisho, kwa sababu wewe ni 10 00:00:28,230 --> 00:00:32,430 kutokana na tupu C file na una kujaza in 11 00:00:32,430 --> 00:00:36,250 OK, hivyo hebu kuvunja hii katika sehemu manageable. 12 00:00:36,250 --> 00:00:38,160 Utasikia wanataka kufungua kadi ya kumbukumbu file. 13 00:00:38,160 --> 00:00:39,900 Hiyo inaonekana rahisi kutosha. 14 00:00:39,900 --> 00:00:43,030 Kisha, kupata mwanzo ya JPG picha. 15 00:00:43,030 --> 00:00:46,740 Mafaili yote juu ya kumbukumbu hii kadi ni kwenda kuwa JPGs. 16 00:00:46,740 --> 00:00:50,840 Basi, mara moja kupata mwanzo, wewe kwenda kufungua JPG mpya, kwamba 17 00:00:50,840 --> 00:00:57,610 ni, kama, kujenga JPG, na kuandika 512 byte wakati mpaka mpya JPG ni 18 00:00:57,610 --> 00:01:02,930 kupatikana, na kumalizia mpango huo, mara kuchunguza mwisho wa faili. 19 00:01:02,930 --> 00:01:06,400 >> Hatua hiyo ya kwanza ya kwanza ni kufungua kadi ya kumbukumbu file. 20 00:01:06,400 --> 00:01:09,850 Lakini unajua hii tayari, na kuna file I / O kazi hiyo kwenda 21 00:01:09,850 --> 00:01:12,030 kuthibitisha muhimu sana. 22 00:01:12,030 --> 00:01:12,820 OK. 23 00:01:12,820 --> 00:01:14,760 Kwa hiyo kile ni JPGs? 24 00:01:14,760 --> 00:01:16,330 Kwa sababu tunahitaji mwanzo. 25 00:01:16,330 --> 00:01:21,310 Naam, JPGs, kama ramani kidogo, ni Utaratibu wa tu ya ka. 26 00:01:21,310 --> 00:01:30,660 Kwa bahati nzuri, kila JPG kuanza na ama 0xff, 0xd8, 0xff, 0xe0, mlolongo moja 27 00:01:30,660 --> 00:01:33,610 ya ka, au nyingine mlolongo wa ka. 28 00:01:33,610 --> 00:01:37,250 >> Hivyo wale ka nne zinaonyesha mwanzo wa JPG. 29 00:01:37,250 --> 00:01:40,780 Hakuna wengine zaidi kuliko wale mchanganyiko mbili ya ka nne. 30 00:01:40,780 --> 00:01:44,840 Na kwa bahati yetu, ukweli mwingine kwamba sisi unaweza kuchukua faida ya ni kwamba kila 31 00:01:44,840 --> 00:01:48,550 JPG ni kuhifadhiwa upande kwa upande juu ya kadi ya kumbukumbu. 32 00:01:48,550 --> 00:01:52,210 Nimekuwa kuwakilishwa muundo wa kadi ya kumbukumbu schematically juu ya hili 33 00:01:52,210 --> 00:01:53,310 slide hapa. 34 00:01:53,310 --> 00:01:59,270 Hapa, kila mraba, kila mstatili, inawakilisha 512 ka, na kuanza 35 00:01:59,270 --> 00:02:01,750 rangi ya katika kwamba sisi si kweli kuwa JPG. 36 00:02:01,750 --> 00:02:05,700 >> Lakini basi sisi hatimaye kugonga kuzuia na nyota. 37 00:02:05,700 --> 00:02:10,940 Hiyo ina maana kwamba kwanza ka nne nje ya wale 512 ni moja ya hizo mbili 38 00:02:10,940 --> 00:02:13,230 kuanzia Utaratibu wa JPG. 39 00:02:13,230 --> 00:02:17,340 Na sisi kwenda huko, na kisha mara moja JPG moja kumalizika, moja ijayo huanza. 40 00:02:17,340 --> 00:02:20,990 Sisi si milele yoyote zaidi gray nafasi kati. 41 00:02:20,990 --> 00:02:25,550 >> Lakini jinsi gani sisi kweli kusoma hii, na kusoma ka 512 ili tuweze kufanya 42 00:02:25,550 --> 00:02:27,500 kulinganisha nafasi ya kwanza? 43 00:02:27,500 --> 00:02:33,470 Naam, hebu kwenda nyuma ya fread, ambayo inachukua katika struct ambayo yana 44 00:02:33,470 --> 00:02:34,470 ka kwamba wewe ni kusoma. 45 00:02:34,470 --> 00:02:36,570 Hivyo ni kwenda kuweka wale walio katika hapo - 46 00:02:36,570 --> 00:02:42,192 kawaida, idadi, na kisha inpointer kwamba wewe ni kusoma kutoka. 47 00:02:42,192 --> 00:02:49,900 Sasa, tunataka kusoma 512 kwa wakati mmoja, na tunataka kuhifadhi hii katika buffer, 48 00:02:49,900 --> 00:02:50,700 Mimi nina kwenda simu yake. 49 00:02:50,700 --> 00:02:54,100 >> Kimsingi, tunakwenda kushikilia kwenye wale ka 512 na kufanya 50 00:02:54,100 --> 00:02:55,500 mambo na hayo, right? 51 00:02:55,500 --> 00:02:58,260 Sisi ni kwenda aidha kwa kulinganisha kwanza ka nne, au tunakwenda 52 00:02:58,260 --> 00:02:59,830 kusoma katika, OK? 53 00:02:59,830 --> 00:03:05,050 Hivyo basi data pointer mapenzi kisha kutumika kama buffer yako, na 54 00:03:05,050 --> 00:03:07,745 inpointer, vizuri, kwamba ni kwenda tu kuwa kumbukumbu ya kadi yako. 55 00:03:07,745 --> 00:03:09,500 >> Nyuma kwa kadi ya kumbukumbu yetu schematic. 56 00:03:09,500 --> 00:03:14,690 Sisi ni kwenda kusoma 512 ka wakati huo, kuhifadhi kila block 512-Byte 57 00:03:14,690 --> 00:03:19,190 ndani ya buffer, kufanya kwenye wale buffer, wale ka 512, mpaka tunajua 58 00:03:19,190 --> 00:03:22,000 hasa nini cha kufanya yao. 59 00:03:22,000 --> 00:03:25,960 Hivyo mwanzo ni si kitu, hivyo tutaweza kusoma buffer, kulinganisha, na 60 00:03:25,960 --> 00:03:28,160 sisi haja ya kufanya kitu chochote kwa hayo. 61 00:03:28,160 --> 00:03:32,030 Na kisha, sisi hatimaye kugonga nyota kuzuia, kwa maana kwamba tumekuwa 62 00:03:32,030 --> 00:03:33,630 kupatikana JPG yetu ya kwanza. 63 00:03:33,630 --> 00:03:36,560 Hivyo buffer sasa kushikilia ka na kwamba JPG. 64 00:03:36,560 --> 00:03:40,220 >> wakati mwingine 512 ka, kwa sababu wao ni si kuzuia nyota, pia ni 65 00:03:40,220 --> 00:03:41,740 sehemu ya kwamba JPG. 66 00:03:41,740 --> 00:03:47,630 Na JPGs ni kuendelea kutoka huko katika, mpaka sisi kugonga JPG ijayo. 67 00:03:47,630 --> 00:03:51,880 Na kisha buffer kisha anashikilia 512 ka kwa kuwa JPG, na 68 00:03:51,880 --> 00:03:53,580 kadhalika, na kadhalika. 69 00:03:53,580 --> 00:03:54,250 OK. 70 00:03:54,250 --> 00:03:58,980 >> Hivyo mara moja kugonga kwanza hoja ya kuzuia, JPG kwanza, jinsi gani unaweza 71 00:03:58,980 --> 00:04:01,910 kweli, vizuri, ni wazi? 72 00:04:01,910 --> 00:04:04,990 Hebu kufanya mpya JPG. 73 00:04:04,990 --> 00:04:08,846 filenames kwa JPG ni kwenda kuwa katika format, simu, namba ya, 74 00:04:08,846 --> 00:04:13,830 number.jpg, kwa kuwa wao ni jina lake katika utaratibu ambao wao ni kupatikana, 75 00:04:13,830 --> 00:04:14,780 kuanzia saa 0. 76 00:04:14,780 --> 00:04:19,890 >> Hivyo JPG kwanza kwamba kupata itakuwa 000.jpg. 77 00:04:19,890 --> 00:04:26,560 Kwa hiyo, pengine ni wazo nzuri kuweka wimbo jinsi JPGs wengi Nimepata hadi sasa. 78 00:04:26,560 --> 00:04:27,610 Hivyo kwamba ni jina la faili. 79 00:04:27,610 --> 00:04:29,660 Lakini jinsi gani unaweza kweli kufanya hivyo? 80 00:04:29,660 --> 00:04:34,310 Naam, sisi ni kwenda kutumia kazi kuitwa sprintf. 81 00:04:34,310 --> 00:04:38,260 kidogo sawa na printf, ambapo unaweza kutumia placeholders kwa masharti, 82 00:04:38,260 --> 00:04:42,420 ila katika kesi hii, sprintf magazeti file nje ndani ya sasa ya 83 00:04:42,420 --> 00:04:45,550 directory, si ndani ya wastaafu. 84 00:04:45,550 --> 00:04:46,120 >> OK. 85 00:04:46,120 --> 00:04:49,950 Kwa hiyo hapa tunaona kwamba tuna cheo, char safu kwamba kuhifadhi 86 00:04:49,950 --> 00:04:55,120 kamba matokeo, na sisi kupita katika jina la string halisi na 87 00:04:55,120 --> 00:04:58,720 placeholder, kama vile tumekuwa kujifunza kwa kufanya na printf. 88 00:04:58,720 --> 00:05:05,530 Lakini kanuni hii kwamba mimi hapa nitakupa 2.jpg, si 002.jpg. 89 00:05:05,530 --> 00:05:09,920 Basi, mimi itabidi kuondoka kwa wewe kujua jinsi ya kurekebisha placeholder kufanya 90 00:05:09,920 --> 00:05:11,920 jina sahihi. 91 00:05:11,920 --> 00:05:12,610 >> OK. 92 00:05:12,610 --> 00:05:17,390 Hivyo mara moja umefanya sprintf'd basi unaweza kufungua faili kwamba, kwa sababu ipo katika 93 00:05:17,390 --> 00:05:22,690 saraka yako, na fopen, kwa kutumia cheo, na kisha mode chochote unataka 94 00:05:22,690 --> 00:05:25,140 kufungua faili kwamba in 95 00:05:25,140 --> 00:05:30,260 Hivyo sasa kwamba tumekuwa kufunguliwa mpya JPG file, sasa tunaweza kuandika 512 ka katika 96 00:05:30,260 --> 00:05:33,320 wakati, mpaka JPG mpya kupatikana. 97 00:05:33,320 --> 00:05:36,640 Basi hebu tuangalie tena katika syntax ya fwrite. 98 00:05:36,640 --> 00:05:40,060 >> Najua kwamba nina kuonyesha hii slide a mengi, lakini mimi nataka tu kuhakikisha kwamba 99 00:05:40,060 --> 00:05:43,530 nyie hawapati pia kuchanganyikiwa, kwa sababu Najua kwamba ni rahisi sana kwa 100 00:05:43,530 --> 00:05:47,000 kuchanganya kwanza na mwisho hoja, hasa. 101 00:05:47,000 --> 00:05:54,390 Lakini kumbuka kwamba wewe ni kuandika kutoka buffer yako katika images nje file. 102 00:05:54,390 --> 00:05:59,250 >> Sasa kwa kuwa wewe kujua jinsi ya kuandika 512 ka katika JPG file yako kwamba wameweza 103 00:05:59,250 --> 00:06:03,230 kuundwa, vizuri, tunataka kuacha kuwa mchakato mara moja tumekuwa kufikiwa mwisho wa 104 00:06:03,230 --> 00:06:06,720 kadi yetu, kwa sababu hakutakuwa na picha yoyote zaidi kwa kupatikana. 105 00:06:06,720 --> 00:06:10,760 Basi hebu kwenda nyuma fread mara moja zaidi, mimi ahadi. 106 00:06:10,760 --> 00:06:15,600 fread anarudi vitu wangapi wa kawaida, ukubwa, walikuwa tayari katika mafanikio. 107 00:06:15,600 --> 00:06:19,440 Kusema ukweli, hii ni kwenda kuwa chochote kupita katika kwa idadi, sawa? 108 00:06:19,440 --> 00:06:24,140 Kwa sababu wewe ni kujaribu kusoma idadi ya mambo ya kawaida, ukubwa. 109 00:06:24,140 --> 00:06:29,380 Lakini kama fread ni si uwezo wa kusoma kwamba idadi ya vipengele, basi itabidi kurudi 110 00:06:29,380 --> 00:06:32,530 chochote idadi ni kusoma kwa mafanikio. 111 00:06:32,530 --> 00:06:36,310 >> Sasa, jambo moja muhimu kutambua ni kwamba kama matumizi ya faili mwingine I / O 112 00:06:36,310 --> 00:06:43,860 kazi kama fgetc, kutakuwa na pia kurudi jinsi vitu vingi ni kusoma kwa mafanikio. 113 00:06:43,860 --> 00:06:48,000 Nini muhimu kuhusu kazi hii ni kwamba kama matumizi ya kazi ndani ya 114 00:06:48,000 --> 00:06:53,190 hali, kutakuwa na kutekeleza yenyewe wakati kuamua kwamba hali, ambayo ni 115 00:06:53,190 --> 00:06:54,340 tu muhimu kweli kweli. 116 00:06:54,340 --> 00:07:00,440 Hivyo kama una hali ya hii, kusema, kama fread buffer, sizeof DOG, 2, 117 00:07:00,440 --> 00:07:04,870 pointer, sawa na sawa na 1, kwamba ina maana kwamba Ningependa kusoma 118 00:07:04,870 --> 00:07:06,540 2 mbwa wakati huo. 119 00:07:06,540 --> 00:07:13,490 Lakini kama fread anarudi 1 badala ya 2 kama ilivyotarajiwa, hiyo ina maana kwamba kuna 2 120 00:07:13,490 --> 00:07:16,480 mbwa wa kushoto katika faili yangu, lakini badala ya 1. 121 00:07:16,480 --> 00:07:22,450 Lakini kama kuirudisha 2, basi mimi bado na wale mbwa 2 ndani ya buffer yangu. 122 00:07:22,450 --> 00:07:26,280 >> Hivyo sasa kwamba inatoa hisia ya jinsi ya kuangalia kwa mwisho wa faili, lakini 123 00:07:26,280 --> 00:07:28,940 hebu kwenda kwa njia ya sasa mantiki. 124 00:07:28,940 --> 00:07:32,460 Je, sisi kweli kipande wote ya mambo haya pamoja? 125 00:07:32,460 --> 00:07:36,880 Mara baada ya sisi kugonga JPG wetu wa kwanza, tangu tunajua kwamba JPGs ni kuhifadhiwa 126 00:07:36,880 --> 00:07:40,910 contiguously, tutaweza kuwa na kuandika mpaka sisi kufikia mwisho wa faili kadi. 127 00:07:40,910 --> 00:07:43,950 Lakini hatutaki kuandika kitu mpaka wakati huo. 128 00:07:43,950 --> 00:07:48,710 Hivyo mambo, si tu kwamba tuko katika mwanzoni mwa msimu mpya JPG, lakini kama 129 00:07:48,710 --> 00:07:50,655 tumekuwa tayari kupatikana JPG au la. 130 00:07:50,655 --> 00:07:55,390 >> Kama Ni mwanzoni mwa msimu mpya JPG, tutaweza unataka karibu JPG faili wetu sasa kama 131 00:07:55,390 --> 00:07:59,110 tuna wazi moja, na wazi mwezi mmoja kuandika ndani. 132 00:07:59,110 --> 00:08:03,340 Kama siyo mwanzo wa JPG mpya, ingawa, tutaweza kuweka sawa JPG file 133 00:08:03,340 --> 00:08:05,910 kufungua na kuandika ndani ya hiyo. 134 00:08:05,910 --> 00:08:10,100 Tutaweza kuandika buffer yetu katika namna yoyote JPG file tuna wazi, mradi 135 00:08:10,100 --> 00:08:12,120 tuna wazi moja, bila shaka. 136 00:08:12,120 --> 00:08:16,190 Kama hatuna kupatikana JPG wetu wa kwanza Hata hivyo, sisi wala kuandika kitu chochote. 137 00:08:16,190 --> 00:08:20,290 Na mchakato huu unaendelea mpaka kufikia mwisho wa faili kadi. 138 00:08:20,290 --> 00:08:23,410 >> Na hatimaye, utasikia wanataka kufanya kuhakikisha kwamba fclose yoyote 139 00:08:23,410 --> 00:08:25,800 files kwamba umefanya fopened. 140 00:08:25,800 --> 00:08:28,360 Mara baada ya wewe ni starehe na dhana, tuangalie baadhi ya 141 00:08:28,360 --> 00:08:30,840 pseudocode, ambayo nimekuwa ni pamoja na hapa. 142 00:08:30,840 --> 00:08:34,830 Kwanza, unataka kufungua faili kadi, na kisha kurudia utaratibu zifuatazo 143 00:08:34,830 --> 00:08:37,144 mpaka wameweza kufikiwa mwisho wa kadi. 144 00:08:37,144 --> 00:08:40,880 Unataka kusoma 512 ka ndani ya buffer. 145 00:08:40,880 --> 00:08:43,934 Kwa kutumia buffer, utasikia wanataka kuangalia kama wewe ni mwanzo wa 146 00:08:43,934 --> 00:08:45,300 JPG mpya au la. 147 00:08:45,300 --> 00:08:48,400 Na jibu la swali hilo mapenzi kuathiri usimamizi file yako - 148 00:08:48,400 --> 00:08:51,940 ambayo files kufungua, ambayo ndio je, karibu. 149 00:08:51,940 --> 00:08:55,220 >> Basi, wewe tayari kupatikana JPG? 150 00:08:55,220 --> 00:08:57,740 Gani wamekuwa kutunza wimbo wa hiyo? 151 00:08:57,740 --> 00:09:01,735 Basi, kulingana na kwamba, itabidi ama kuandika katika JPG sasa kwamba 152 00:09:01,735 --> 00:09:07,090 kuwa wazi, au si kuandika wakati wote, kwa sababu una hakuonekana JPG bado. 153 00:09:07,090 --> 00:09:10,870 Hatimaye, mara moja Umefikia mwisho wa file, utasikia wanataka karibu yoyote 154 00:09:10,870 --> 00:09:12,590 files kwamba una wazi iliyobaki. 155 00:09:12,590 --> 00:09:14,590 Tunataka kuwa na tidy hapa. 156 00:09:14,590 --> 00:09:18,790 >> Na kwa kuwa, umefanya zinalipwa yote ya files kukosa na kwamba kumbukumbu 157 00:09:18,790 --> 00:09:21,620 kadi, ambayo ni feat pretty ajabu. 158 00:09:21,620 --> 00:09:23,430 Hivyo pat mwenyewe juu ya nyuma. 159 00:09:23,430 --> 00:09:27,560 Lakini, kuna moja zaidi hiki kwa Pset, ambayo ni kugombea. 160 00:09:27,560 --> 00:09:30,920 Utakuta kwamba wote wa picha kwamba umefanya zinalipwa ni kweli 161 00:09:30,920 --> 00:09:32,820 picha za wafanyakazi CS50 ya. 162 00:09:32,820 --> 00:09:38,500 Hivyo kama wewe ni juu ya chuo au mahali fulani karibu, basi unaweza kuchukua picha na 163 00:09:38,500 --> 00:09:42,600 wafanyakazi, na sehemu ambayo ina picha zaidi kwa wafanyakazi 164 00:09:42,600 --> 00:09:46,940 kutoka mafaili yao zinalipwa mapenzi kupata tuzo ya kutisha. 165 00:09:46,940 --> 00:09:50,650 Pamoja na kwamba, basi kumaliza kuokoa pset. 166 00:09:50,650 --> 00:09:53,600 Jina langu ni Zamyla, na hii ni CS50. 167 00:09:53,600 --> 00:10:01,835