使用free（）后，Valgrind报告丢失的字节数

Question

在阅读内存分配后，我一直在用C语言尝试一些东西。一切似乎都非常柔软和引人注目，直到我陷入这个程序。它按预期工作，但valgrind清楚地陈述了一个完全不同的故事。这是我的计划：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define NSTRINGS 3

int main()
{
    char **v = NULL;
    int sum = 0;
    char str[80]={'\0'};
    int i = 0, pos = 0;
    v = (char**) calloc((NSTRINGS * sizeof(char*)),1);

    while(1)
    {
        for(i = 0; i < NSTRINGS; i++)
        {
            printf("[%d] ", i+1);
            if(v[i] == NULL)
                printf("(Empty)\n");
            else
                printf("%s\n", v[i]);
        }

        do        
        {
            printf("New string's position (1 to %d): ", NSTRINGS);
            scanf("%d", &pos);
            getchar(); /* discards '\n' */
        }
        while(pos < 0 || pos > NSTRINGS);

        if (pos == 0){
            i = 0;
            break;
        }
        else{
            printf("New string: ");
            fgets(str, 80, stdin);
            str[strlen(str) - 1] = '\0';
            v[pos - 1] = realloc(v[pos - 1], strlen(str)+1);
            strcpy(v[pos - 1], str);
        }
    }
    free(v);
    v = NULL;
    return 0;
}

唯一的目标是根据所需的空间分配3个字符串（以保留未使用的空间）。但是，即使在使用free（v）之后，这也是valgrind返回给我的东西（按顺序填充它们1 2 3然后0）：

[...]
==6760== 
==6760== HEAP SUMMARY:
==6760==     in use at exit: 20 bytes in 3 blocks
==6760==   total heap usage: 6 allocs, 3 frees, 2,092 bytes allocated
==6760== 
==6760== 20 bytes in 3 blocks are definitely lost in loss record 1 of 1
==6760==    at 0x4C2FA3F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6760==    by 0x4C31D84: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6760==    by 0x4009EB: main (in /home/esdeath/Prog/PL2/a.out)
==6760== 
==6760== LEAK SUMMARY:
==6760==    definitely lost: 20 bytes in 3 blocks
==6760==    indirectly lost: 0 bytes in 0 blocks
==6760==      possibly lost: 0 bytes in 0 blocks
==6760==    still reachable: 0 bytes in 0 blocks
==6760==         suppressed: 0 bytes in 0 blocks
==6760== 
==6760== For counts of detected and suppressed errors, rerun with: -v
==6760== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0

有了这个，我有两个问题我一直试图回答，但我担心我的经历现在并没有真正让我：

• 首先，它表明我有3个alloc，即使我从未使用/达到realloc函数。这是否意味着calloc函数单独使用3个alloc？如果是这样，为什么？
• 其次，我怎样才能完全释放20个字节（在这种情况下）？我真的很困惑......

提前致谢。

---

旁注：我认为“realloc”可能会返回NULL（如果失败），我将其添加到程序中。除非它被错误地放置，Valgrind继续报告同样的问题，所以我最终删除它（在撤消过程中）......

Answer 1

你不是freeing由realloc分配的内存。加

for (int i = 0; i < NSTRINGS; ++i)
    free(v[i]);

之前

free(v);