分段错误错误（NEW repost） [英] Segmentation fault error (NEW repost)

问题描述

In my code I changed some lines.

我收到分段错误，这里是valgrind的输出：

I get a segmentation fault, and here's valgrind's output:

==3587== Invalid read of size 4
==3587==    at 0x5E27CD0: fwrite (iofwrite.c:41)
==3587==    by 0x42D989: main (recover.c:61)
==3587==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==3587== 
==3587== 
==3587== Process terminating with default action of signal 11 (SIGSEGV)
==3587==  Access not within mapped region at address 0x0
==3587==    at 0x5E27CD0: fwrite (iofwrite.c:41)
==3587==    by 0x42D989: main (recover.c:61)
==3587==  If you believe this happened as a result of a stack
==3587==  overflow in your program's main thread (unlikely but
==3587==  possible), you can try to increase the size of the
==3587==  main thread stack using the --main-stacksize= flag.
==3587==  The main thread stack size used in this run was 8388608.
==3587== 
==3587== HEAP SUMMARY:
==3587==     in use at exit: 568 bytes in 1 blocks
==3587==   total heap usage: 1 allocs, 0 frees, 568 bytes allocated
==3587== 
==3587== LEAK SUMMARY:
==3587==    definitely lost: 0 bytes in 0 blocks
==3587==    indirectly lost: 0 bytes in 0 blocks
==3587==      possibly lost: 0 bytes in 0 blocks
==3587==    still reachable: 568 bytes in 1 blocks
==3587==         suppressed: 0 bytes in 0 blocks
==3587== Reachable blocks (those to which a pointer was found) are not shown.
==3587== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==3587== 
==3587== For counts of detected and suppressed errors, rerun with: -v
==3587== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
Segmentation fault

我的尝试：

What I have tried:

int main()
{
    typedef uint8_t BYTEINBITS;

    int pictcount = 0;
    
    
    FILE* card = fopen("card.raw", "r");
    
    FILE* newjpg = NULL;
  
     while ( true )
    {
        BYTEINBITS buffer[512];

         
        if ( fread( buffer, 512 * sizeof(char), 1, card) != 1 )
        {
           return 3;
        
        }
 
         
        bool jpg = true;
        
        if ( !( ( buffer[0] == 255 ) && ( buffer[1] == 216 ) && ( buffer[2] == 255) && ( buffer[3] > 224 ) ) )         
        {
            jpg = false;
        }
 
         
        if (jpg == true)
        {
            
            pictcount++;
            char title[8];
            sprintf(title,"%03d.jpg", pictcount);
            
            newjpg  = fopen(title, "w");
        
        }
         
            fwrite(buffer, 512 * sizeof(char), 1, newjpg);
         
    }
    
     fclose(card);
     fclose(newjpg);
    
}

推荐答案

在特定情况下代码可能会失败：

• 打开文件时 card.raw 失败（例如当前工作目录中不存在）：检查 card 不是 NULL
• 当 pictcount 大于999时（可能）不会发生实际代码）：使标题数组更大
• 当 pict.raw 不是JPEG文件时（使用 newjpg = NULL 调用 fwrite ：放置第一个 fread 循环前调用和JPEG检查

The code can fail under specific circumstances:

• When opening the file card.raw fails (e.g. does not exist in the current working directory): Check if card is not NULL
• When pictcount is greater than 999 (may not happen with the actual code): Make the title array larger
• When pict.raw is not a JPEG file (fwrite is called with newjpg = NULL): Place the first fread call and the JPEG check before the loop

错误信息告诉你所有。

The error message tells you all.

==3587== Invalid read of size 4
==3587==    at 0x5E27CD0: fwrite (iofwrite.c:41)
==3587==    by 0x42D989: main (recover.c:61)
==3587==  Address 0x0 is not stack'd, malloc'd or (recently) free'd

buffer 是一个数组，而wa你在 fwrite 中使用它是错误的， fwrite 使用的值是的包含缓冲区而不是其地址。

buffer is an array, and the way you use it in fwrite is wrong, the value used by fwrite is the contain of buffer instead of its address.

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