无法释放内存

Question

gcc 4.4.4 c89

我有以下功能，但我不能释放内存。我在Valgrind中得到的消息是怀疑getline函数。但是，我可以释放函数末尾的文件指针。所以它不可能是那样的。

我有一个全局的指针数组，指向字符'candidate_names‘。但是，我还没有为它分配任何内存。

非常感谢你的建议，

我在valgrind中得到的消息如下所示。

HEAP SUMMARY:
==4021==     in use at exit: 840 bytes in 7 blocks
==4021==   total heap usage: 22 allocs, 15 frees, 1,332 bytes allocated
==4021== 
==4021== Searching for pointers to 7 not-freed blocks
==4021== Checked 48,412 bytes
==4021== 
==4021== 840 bytes in 7 blocks are still reachable in loss record 1 of 1
==4021==    at 0x4005BDC: malloc (vg_replace_malloc.c:195)
==4021==    by 0xAAE38D: getdelim (iogetdelim.c:68)
==4021==    by 0xAAADD2: getline (getline.c:34)
==4021==    by 0x804892B: load_candidates (candidate.c:61)
==4021==    by 0x8048686: main (driver.c:24)

我的源码：

#define NUMBER_OF_CANDIDATES 7
static char *candidate_names[NAME_SIZE] = {0};

int load_candidates()
{
    FILE *fp = NULL;
    size_t i = 0;
    ssize_t read = 0;
    size_t n = 0;
    char *found = NULL;

    fp = fopen("votes.txt", "r");

    /* open the votes file */
    if(fp == NULL) {
        fprintf(stderr, "Cannot open votes file [ %s ]\n", strerror(errno));
        return FALSE;
    }

    /* fill the structure with candidates */
    for(i = 0; i < NUMBER_OF_CANDIDATES; ) {
        read = getline(&candidate_names[i], &n ,fp);
        if(read == -1) {
            fprintf(stderr, "Cannot read candidate [ %d ] [ %s ]\n",
                    i, strerror(errno));
            candidate_names[i] = "Invalid candidate";
            i++;
            continue;
        }
        /* Just ignore the key work in the text file */
        if(strcmp("CANDIDATES\n", candidate_names[i]) != 0) {
            /* Find and remove the carriage return */
            found = strchr(candidate_names[i], '\n');
            if(found != NULL) {
                /* Remove the carriage return by nul terminating */
                *found = '\0';
            }
            i++;
        }
    }

    fclose(fp);

    return TRUE;
}

编辑并释放candidate_names ======

All heap blocks were freed -- no leaks are possible
==4364== 
==4364== ERROR SUMMARY: 84 errors from 2 contexts (suppressed: 12 from 8)
==4364== 
==4364== 42 errors in context 1 of 2:
==4364== Invalid free() / delete / delete[]
==4364==    at 0x40057F6: free (vg_replace_malloc.c:325)
==4364==    by 0x8048A95: destroy_candidate (candidate.c:107)
==4364==    by 0x8048752: main (driver.c:44)
==4364==  Address 0x401e1b8 is 0 bytes inside a block of size 120 free'd
==4364==    at 0x40057F6: free (vg_replace_malloc.c:325)
==4364==    by 0x8048A95: destroy_candidate (candidate.c:107)
==4364==    by 0x8048752: main (driver.c:44)
==4364== 
==4364== 
==4364== 42 errors in context 2 of 2:
==4364== Invalid read of size 1
==4364==    at 0x400730E: strcmp (mc_replace_strmem.c:426)
==4364==    by 0x8048A7F: destroy_candidate (candidate.c:106)
==4364==    by 0x8048752: main (driver.c:44)
==4364==  Address 0x401e1b8 is 0 bytes inside a block of size 120 free'd
==4364==    at 0x40057F6: free (vg_replace_malloc.c:325)
==4364==    by 0x8048A95: destroy_candidate (candidate.c:107)
==4364==    by 0x8048752: main (driver.c:44)


void destroy_candidate()
{
    size_t i = 0;
    for(i = 0; i < NUMBER_OF_CANDIDATES; i++) {
        if(strcmp(candidate_names[i], "Invalid candidate") != 0) {
            free(candidate_names[i]);
        }
    }
}

使用main.c =====================中的代码进行编辑

typedef struct Candidate_data_t {
    size_t candidate_data_id;
    Candidates_t *candidate;
} Candidate_data;

static Candidate_data* create_candidate_data(Candidates_t *candidate, size_t i);
static void destroy_candidata_data(Candidate_data *cand_data);

int main(void)
{
    Candidates_t *candidate = NULL;
    Candidate_data *cand_data[NUMBER_OF_CANDIDATES] = {0};
    size_t i = 0;

    load_candidates();

    for(i = 0; i < NUMBER_OF_CANDIDATES; i++) {
         candidate = create_candidates(i);
         if(candidate == NULL) {
             fprintf(stderr, "Cannot failed to initalize candidate [ %d ]\n", i);
         }

         /* Create array of candidates */
         cand_data[i] = create_candidate_data(candidate, i);
         fill_candidates(cand_data[i]->candidate);
    }

    /* Display each candidate */
    for(i = 0; i < NUMBER_OF_CANDIDATES; i++) {
        display_candidate(cand_data[i]->candidate);
        printf("\n");
    }

    for(i = 0; i < NUMBER_OF_CANDIDATES; i++) {
        destroy_candidata_data(cand_data[i]);
    }

    return 0;
}

static Candidate_data* create_candidate_data(Candidates_t *candidate, size_t id)
{
    Candidate_data *cand_data = NULL;

    cand_data = malloc(sizeof *cand_data);

    if(cand_data == NULL) {
        fprintf(stderr, "Failed to allocate memory [ %s ]\n",
                strerror(errno));

        return NULL;
    }
    cand_data->candidate_data_id = id;
    cand_data->candidate = candidate;

    return cand_data;
}

static void destroy_candidata_data(Candidate_data *cand_data)
{
    destroy_candidate(cand_data->candidate);
    free(cand_data);
}

Answer 1

getline分配存储在candidate_names指针数组中的内存。这些指针不会被释放。当您使用完它们时，您应该调用：

for(i = 0; i < NUMBER_OF_CANDIDATES; i++)
{
    if (strcmp(candidate_names[i], "Invalid candidate") != 0)
        free(candidate_names[i]);
}

此外，该数组应声明为：

static char *candidate_names[NUMBER_OF_CANDIDATES];

在你的getline之前，你需要：

candidate_names[i] = NULL;

不需要NAME_SIZE，因为该内存是动态分配的，除非您在其他地方将其用于输入验证或其他用途。

Answer 2

看一看getline() man page。

如果*lineptr为空，则getline()将分配一个缓冲区来存储该行，该缓冲区应由用户程序释放。(在这种情况下，*n中的值被忽略。)

在程序结束时，您需要遍历candidate_names数组并在非NULL条目上调用free，但在这种情况下，您不能像@pmg在他的回答中指出的那样执行candidate_names[i] = "Invalid candidate";，因为您将尝试释放字符串文字。

还要注意：

或者，在调用

()之前，*lineptr可以包含一个指针，指向一个大小为*n字节的malloc(3)-allocated缓冲区。如果缓冲区不足以容纳该行，getline()会使用realloc(3)调整它的大小，并根据需要更新*lineptr和*n。

在这两种情况下，在成功调用时，*lineptr和*n将分别更新以反映缓冲区地址和分配的大小。

Answer 3

什么是candidate_names？它是一个指针数组。

当你这样做的时候

candidate_names[i] = "Invalid candidate";

将指针赋值给字符串文字。也许在稍后的程序中，你会想要free它。这是一个NO-NO！

在任何情况下，candidate_names[i]之前的值都会丢失。如果值不是NULL，那么您只是泄漏了一些内存。