为什么我无法释放内存？无效的 free() / delete / delete[] / realloc()

Question

我正在尝试改进丑陋的 C 代码，它会导致内存泄漏。 Valgrind 点数：

==19046== 1,001 bytes in 1 blocks are definitely lost in loss record 1 of 1
==19046==    at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==19046==    by 0x109D0B: save_params (ugly.c:188)

save_params很长，去掉其他部分后可以这样呈现：

/* Save params to file */
int save_params(int nb_iter) {
    char *word = malloc(sizeof(char) * MAX_STRING_LENGTH + 1); // <----- ugly.c:188 line 
    FILE *fid, *fout, *fgs;

        for (a = 0; a < vocab_size; a++) {
            if (fscanf(fid,format,word) == 0) {free(word); return 1;}
            if (strcmp(word, "<unk>") == 0) {free(word); return 1;}
            fprintf(fout, "%s",word);
            //...
            if (save > 0) {
                fprintf(fgs, "%s",word);
            if (fscanf(fid,format,word) == 0) {free(word); return 1;}
        }

        if (use_unk_vec) {
            word = "<unk>";
            fprintf(fout, "%s",word);
        }

        fclose(fid);
        fclose(fout);
        if (save > 0) fclose(fgs);

    }
    free(word); <--------- that free is "invalid"
    return 0;
}

Valgrind 输出：

==19046== Invalid free() / delete / delete[] / realloc()
==19046==    by 0x10AAC6: save_params (ugly.c:288)
==19046== 
==19046== HEAP SUMMARY:
==19046==     in use at exit: 1,001 bytes in 1 blocks
==19046==   total heap usage: 78 allocs, 78 frees, 13,764,515 bytes allocated
==19046== 
==19046== 1,001 bytes in 1 blocks are definitely lost in loss record 1 of 1
==19046==    by 0x109D0B: save_params (ugly.c:188)

==19046== LEAK SUMMARY:
==19046==    definitely lost: 1,001 bytes in 1 blocks
==19046==    indirectly lost: 0 bytes in 0 blocks

==19046== 
==19046== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)

你能告诉我我做错了什么吗？我应该如何释放 malloc 保留的内存？

Answer 1

你不能释放它，因为你做了:

word = "<unk>";

现在word不再指向你分配的内存，它指向这个文字串。你有内存泄漏，当你试图释放它时出错。

没有必要在那里重新分配 word。只需将文字字符串写入文件即可。

if (use_unk_vec) {
    fprintf(fout, "<unk>");
}

也不清楚为什么首先需要使用 malloc() 和 free()。由于您在此函数中仅使用 word，因此您应该将其声明为本地数组：

char word[MAX_STRING_LENGTH + 1];

为什么我无法释放内存？无效的 free() / delete / delete[] / realloc()

Why I am not able to free memory? Invalid free() / delete / delete[] / realloc()

c

memory

gcc

valgrind

memory-leaks