C 中的 Valgrind 无效的 free() / delete / delete[] / realloc()

Question

Valgrind 告诉我，内存中有泄漏，我试图释放它，但我想它没有正确完成。有任何想法吗？谢谢。

Invalid free() / delete / delete[] / realloc() at 0x4C27D4E: free (vg_replace_malloc.c:427)

by 0x400C00: main (main.c:149)

Address 0x51ba138 is 0 bytes after a block of size 8 alloc'd

at 0x4C28BED: malloc (vg_replace_malloc.c:263) by 0x400B0E: main (main.c:119)

HEAP SUMMARY: in use at exit: 2 bytes in 1 blocks total heap usage: 5 allocs, 5 frees, 14 bytes allocated

2 bytes in 1 blocks are definitely lost in loss record 1 of 1

at 0x4C28BED: malloc (vg_replace_malloc.c:263)

by 0x40084F: strdup (main.c:19)

by 0x4009C4: permute (main.c:83)

by 0x400B9C: main (main.c:138)

char *strdup (const char *s)
{
    char *d = malloc (strlen (s) + 1);  // Space for length plus null //line 19
    if (d == NULL) {
        return NULL;            // No memory
    }
    strcpy (d, s);              // Copy the characters
    return d;                   // Return the new string
}

void permute (char *arrayOfPermutations, int startIndex, int stopIndex,
            char ***permuts)
{
    int i;
    if (startIndex == stopIndex) {
        **permuts = strdup (arrayOfPermutations);       //save generated string //line 83
        *permuts += 1;          //increment location
    } else {
        for (i = startIndex; i <= stopIndex; i++) {
            swap ((arrayOfPermutations + startIndex),
                (arrayOfPermutations + i));
            permute (arrayOfPermutations, startIndex + 1, stopIndex, permuts);
            swap ((arrayOfPermutations + startIndex),
                (arrayOfPermutations + i));
        }
    }
}

int main (int argc, char *argv[])
{
    char *stringInput, c = 0;
    unsigned int j = 0, i = 0, stringSize, facto;
    char **permuts, **work;

    stringInput = (char *) malloc (sizeof (char));

    while (c != '\n') {
        c = getc (stdin);       //read the input from keyboard standard input
        stringInput = (char *) realloc (stringInput, (j + 1) * sizeof (char));  //re-allocate (resize) memory for character read to be stored
        stringInput[j] = c;     //store read character by making pointer point to c
        j++;
    }

    stringInput[j - 1] = '[=10=]';  //add null termination
    stringSize = strlen (stringInput);
    facto = factorial (stringSize);

    permuts = (char **) malloc (facto * sizeof (char *));       // allocate n! pointers //line 119
    work = permuts;

    printf ("String size: %d\n", stringSize);

    ...some printfs here...permute (stringInput, 0, stringSize - 1, &work);     //creates permutations of chars //line 138

    qsort (permuts, facto, sizeof (char *), compare);   //sorts strings alphabetically

    for (i = 0; i <= facto - 1; i++) {
        printf ("\"%s\"\n", permuts[i]);
    }

    free (work);                //free the memory //line 149
    free (permuts);             //free the memory
    free (stringInput);         //free the memory
}

Answer 1

在我阅读你的代码之前。 Valgrind 报告无效释放错误不是因为内存泄漏，而是您尝试释放无效内存（或多次释放同一内存）。使用编译器标志 -g（gdb 调试）编译您的代码，将启用更多调试信息，使来自 valgrind 的回溯更好。

快速猜测：

  ..
  for(i = 0; i <= facto-1; i++)
   {
    printf("\"%s\"\n", permuts[i]);
    free (permuts[i]); /* free the text, allocated with strdup(); */
  }

  free(permuts);//free the memory
  free(stringInput);//free the memory
}

Answer 2

除其他问题外，您的代码的一个主要问题是：

double free or corruption (out): 0x000000000074a060 ***

原因：

char **permuts, **work;
...
work = permuts;
...
free (work);                //free the memory //line 149
free (permuts);             //free the memory

您正在释放同一块内存两次。

C 中的 Valgrind 无效的 free() / delete / delete[] / realloc()

Valgrind Invalid free() / delete / delete[] / realloc() in C

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malloc

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valgrind

memory-leaks