在执行 CS50 任务时
recover#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
int main(int argc, char *argv[])
{
if (argc != 2) {
printf("Usage: ./recover [argument]\n");
return 1;
}
FILE* sdCard = fopen(argv[1], "r");
if (sdCard == NULL) {
printf("Couldn't open %s in read-mode", argv[1]);
return 1;
}
uint8_t buffer[512];
// ###.png\0 => 8 characters
char file_name[8];
int fileNumber = 0;
FILE* recoveredJPG;
char* zeroes = NULL;
int foundFirstJPEG = 0;
// Create files
while(fread(buffer, sizeof(uint8_t), 512, sdCard)) {
if (buffer[0] == 0xFF && buffer[1] == 0xD8 && buffer[2] == 0xFF && (buffer[3] & 0xFF) == 0xE0) {
foundFirstJPEG = 1;
if (fileNumber < 10) {
zeroes = malloc(3*sizeof(char));
if (zeroes == NULL) {
printf("Memory allocation failed!");
fclose(sdCard);
sdCard = NULL;
if (recoveredJPG != NULL) {
fclose(recoveredJPG);
recoveredJPG = NULL;
}
return 1;
}
strcpy(zeroes, "00");
} else if (fileNumber >= 10) {
zeroes = malloc(2*sizeof(char));
if (zeroes == NULL) {
printf("Memory allocation failed!");
fclose(sdCard);
sdCard = NULL;
if (recoveredJPG != NULL) {
fclose(recoveredJPG);
recoveredJPG = NULL;
}
return 1;
}
strcpy(zeroes, "0");
}
if (zeroes == NULL) {
printf("Memory allocation failed!");
fclose(sdCard);
sdCard = NULL;
if (recoveredJPG != NULL) {
fclose(recoveredJPG);
recoveredJPG = NULL;
}
return 1;
}
sprintf(file_name, "%s%i.jpg", zeroes, fileNumber);
if (recoveredJPG != NULL){
fclose(recoveredJPG);
recoveredJPG = NULL;
}
recoveredJPG = fopen(file_name, "w");
if (recoveredJPG == NULL) {
printf("Error while creating %s.", file_name);
free(zeroes);
zeroes = NULL;
fclose(sdCard);
sdCard = NULL;
return 1;
}
free(zeroes);
zeroes = NULL;
fwrite(buffer, sizeof(uint8_t), 512, recoveredJPG);
fileNumber++;
} else if (foundFirstJPEG) {
fwrite(buffer, sizeof(uint8_t), 512, recoveredJPG);
}
}
if (recoveredJPG != NULL) {
fclose(recoveredJPG);
recoveredJPG = NULL;
}
fclose(sdCard);
sdCard = NULL;
if (zeroes != NULL) {
free(zeroes);
zeroes = NULL;
}
return 0;
}
我尝试了一切，删除后将每个文件清空，每次返回之前释放每个指针，确保在访问之前检查每个指针不为空。我仍然遇到可能的分段错误。
这是 valgind 的输出：
==3125== Memcheck, a memory error detector
==3125== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==3125== Using Valgrind-3.22.0 and LibVEX; rerun with -h for copyright info
==3125== Command: ./recover card.raw
==3125==
==3125== Conditional jump or move depends on uninitialised value(s)
==3125== at 0x10948C: main (recover.c:81)
==3125== Uninitialised value was created by a stack allocation
==3125== at 0x1091C4: main (recover.c:7)
==3125==
==3125== Use of uninitialised value of size 8
==3125== at 0x4A0E294: fclose@@GLIBC_2.2.5 (iofclose.c:48)
==3125== by 0x10949D: main (recover.c:82)
==3125== Uninitialised value was created by a stack allocation
==3125== at 0x1091C4: main (recover.c:7)
==3125==
==3125== Use of uninitialised value of size 8
==3125== at 0x4A0E33C: fclose@@GLIBC_2.2.5 (iofclose.c:51)
==3125== by 0x10949D: main (recover.c:82)
==3125== Uninitialised value was created by a stack allocation
==3125== at 0x1091C4: main (recover.c:7)
==3125==
==3125== Invalid read of size 8
==3125== at 0x4A0E353: fclose@@GLIBC_2.2.5 (iofclose.c:51)
==3125== by 0x10949D: main (recover.c:82)
==3125== Address 0x8 is not stack'd, malloc'd or (recently) free'd
==3125==
==3125==
==3125== Process terminating with default action of signal 11 (SIGSEGV): dumping core
==3125== Access not within mapped region at address 0x8
==3125== at 0x4A0E353: fclose@@GLIBC_2.2.5 (iofclose.c:51)
==3125== by 0x10949D: main (recover.c:82)
==3125== If you believe this happened as a result of a stack
==3125== overflow in your program's main thread (unlikely but
==3125== possible), you can try to increase the size of the
==3125== main thread stack using the --main-stacksize= flag.
==3125== The main thread stack size used in this run was 8388608.
==3125==
==3125== HEAP SUMMARY:
==3125== in use at exit: 4,571 bytes in 3 blocks
==3125== total heap usage: 3 allocs, 0 frees, 4,571 bytes allocated
==3125==
==3125== 3 bytes in 1 blocks are still reachable in loss record 1 of 3
==3125== at 0x4846828: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==3125== by 0x1092F2: main (recover.c:38)
==3125==
==3125== 472 bytes in 1 blocks are still reachable in loss record 2 of 3
==3125== at 0x4846828: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==3125== by 0x4A0EE6E: __fopen_internal (iofopen.c:65)
==3125== by 0x4A0EE6E: fopen@@GLIBC_2.2.5 (iofopen.c:86)
==3125== by 0x109210: main (recover.c:13)
==3125==
==3125== 4,096 bytes in 1 blocks are still reachable in loss record 3 of 3
==3125== at 0x4846828: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==3125== by 0x4A0E1A4: _IO_file_doallocate (filedoalloc.c:101)
==3125== by 0x4A1E513: _IO_doallocbuf (genops.c:347)
==3125== by 0x4A1CF3B: _IO_file_xsgetn (fileops.c:1288)
==3125== by 0x4A0F48A: fread (iofread.c:38)
==3125== by 0x10927A: main (recover.c:33)
==3125==
==3125== LEAK SUMMARY:
==3125== definitely lost: 0 bytes in 0 blocks
==3125== indirectly lost: 0 bytes in 0 blocks
==3125== possibly lost: 0 bytes in 0 blocks
==3125== still reachable: 4,571 bytes in 3 blocks
==3125== suppressed: 0 bytes in 0 blocks
==3125==
==3125== For lists of detected and suppressed errors, rerun with: -s
==3125== ERROR SUMMARY: 4 errors from 4 contexts (suppressed: 0 from 0)
/opt/cs50/bin/valgrind: line 13: 3125 Segmentation fault (core dumped) /usr/bin/valgrind "$@"
PS：请不要提供任何有关如何更有效地解决 CS50 任务
recover.cPPS：当我自己运行文件时，我没有收到错误，一切都正常运行。
感谢您的帮助。
好吧，你已经让 Valgrind 仔细研究它了，我们只需要解释这些消息：
条件跳转或移动取决于未初始化的值 ==3125==位于0x10948C：主要（recover.c：81）
是的，您在各处都使用
recoveredJPGfopenFILE* recoveredJPG = NULL;此外，出于可读性原因，程序可以拆分为较小的函数，而不是使用多个嵌套
if