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我在使用 valgrind 时得到这个输出：

==19923== Invalid read of size 1
==19923==    at 0x52CCCC0: vfprintf (vfprintf.c:1632)
==19923==    by 0x52F4772: vasprintf (vasprintf.c:59)
==19923==    by 0x52D3A56: asprintf (asprintf.c:35)
==19923==    by 0x400D77: addToList (pa1.c:124)
==19923==    by 0x4010AF: md5Hash (pa1.c:220)
==19923==    by 0x401138: newFile (pa1.c:244)
==19923==    by 0x401260: searchDirects (pa1.c:280)
==19923==    by 0x401451: main (pa1.c:339)
==19923==  Address 0x585b720 is 0 bytes inside a block of size 27 free'd
==19923==    at 0x4C2EDEB: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==19923==    by 0x401144: newFile (pa1.c:246)
==19923==    by 0x401260: searchDirects (pa1.c:280)
==19923==    by 0x401382: directoryCheck (pa1.c:312)
==19923==    by 0x4012CD: searchDirects (pa1.c:290)
==19923==    by 0x401451: main (pa1.c:339)
==19923==  Block was alloc'd at
==19923==    at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==19923==    by 0x52F47D7: vasprintf (vasprintf.c:73)
==19923==    by 0x52D3A56: asprintf (asprintf.c:35)
==19923==    by 0x40112C: newFile (pa1.c:239)
==19923==    by 0x401260: searchDirects (pa1.c:280)
==19923==    by 0x401382: directoryCheck (pa1.c:312)
==19923==    by 0x4012CD: searchDirects (pa1.c:290)
==19923==    by 0x401451: main (pa1.c:339)

这是我将其缩小为代码中的问题的地方：

else
{    
    currentList = headList;
    printf("This is where I will put the code to create the Linked list!\n");
    if(currentList != 0)
    {
        while(currentList->nextList != 0)
        {
            if(currentList->key = key)
            {
                asprintf(&buff, "%s %s", currentList->value, dirValue); // PROBLEM IS HERE
                printf("Here is the new string that holds the directory paths: %s\n", buff);
                currentList->value = buff;
                free(buff);
                printf("Here is the new string that holds the directory paths: %s\n", currentList->value);
                return;
            }
            currentList = currentList->nextList;
        }

        currentList->nextList = malloc(sizeof(struct List));
        printf("Adding a new node\n");
        //Reached the end of the Linked list and didn't find the
        //same key so create a new node.
        currentList = currentList->nextList;
        currentList->key = key;
        currentList->nextList = NULL;
        currentList->value = dirValue;
    }
}

我有很多错误，我觉得提供整个 valgrind 输出会有点矫枉过正。我遇到的所有错误都会回到我使用 asprintf() 的地方("addToList (pa1.c:124)" line in the report)。在我初始化的代码上方char *buff = NULL;，并currentList->value保存一个我想使用 asprintf 附加到的字符串。任何关于我为什么会收到大量 Invalid read size 1 错误的猜测都将不胜感激。此外，当我从 asprintf() 打印出结果时，字符串会按预期附加，谢谢。

4

1 回答 1

2

无效读取位于已释放内存块的开头；您在释放内存后尝试使用它。 

currentList->value = buff;
free(buff);
printf("Here is the new string that holds the directory paths: %s\n", currentList->value);
return;

你currentList->value = buff;在 中使用printf()，但你刚刚释放了buff. 这预示着一场即将到来的灾难。如果currentList->value要在 之后用于调用函数return，那么您将遇到重大问题。

您可以通过移动printf()前的来修复一个警告free()，但代码看起来您​​将遇到重大问题。删除可能会更好free(buff);——尽管您必须找出实际释放数据的位置。

于 2017-01-16T05:51:59.730 回答