我不明白为什么我肯定会丢失内存块

Question

作为一个项目，我正在创建一个学生数据库。但是根据 valgrind，我的程序中存在内存泄漏，我不知道为什么。 我真的不能说更多：我不明白为什么记忆肯定会丢失。

学生结构：

typedef struct {
    char student_number[7];
    char *first_name;
    char *last_name;
    int round_points[6];
} Student;

免责声明：我正在使用 gcc 选项 -std=c99，所以我必须实现自己的 strdup()。

重要的代码片段：

char *copy_string(const char *string) {
    int len = strlen(string);
    char *copy = calloc(len + 1, sizeof(char));
    if (copy == NULL)
        return NULL;
    strcpy(copy, string);
    /* copy[len] = '\0'; */
    return copy;
}

char **parse_one_line_params(const char *one_line, int param_count) {
    char *copy = copy_string(one_line);
    if (copy == NULL)
        return NULL;
    //copy_start is used to free the copy string in the end
    char *copy_start = copy;
    //It is assumed that one_line is of the form COMMAND|SPACE|ARGUMENTS
    //Move pointer to the first important character
    copy += 2;
    const char *separator = " ";
    char **content = malloc(sizeof(char *) * param_count);
    if (content == NULL)
        return NULL;
    int occurrences = 0;
    char *delimiter_start;
    while ((delimiter_start = strstr(copy, separator)) != NULL) {
        delimiter_start[0] = '\0';
        char *sub_string = copy_string(copy);
        if (sub_string == NULL)
            return NULL;
        if (sub_string[0] != '\0') {
            content[occurrences] = sub_string;
        }
        //Since separator is of the length of one
        copy = delimiter_start + 1;
        occurrences++;
    }
    //param n - 1 will be assigned from the last portion of copy
    if (occurrences != param_count - 1)
        return NULL;
    int last_len = strlen(copy);
    if (last_len > 0 && copy[last_len - 1] == '\n')
        copy[last_len - 1] = '\0';
    content[occurrences] = copy_string(copy);
    free(copy_start);
    return content;
}

char **deliver_payload(const char *one_line, int param_count) {
    if (one_line[1] != ' ') {
        printf("Command was longer than one character.\nPlease see manual for instructions\n");
        return NULL;
    }
    char **payload = parse_one_line_params(one_line, param_count);
    if (payload == NULL) {
        printf("Invalid arguments for given command\n");
        return NULL;
    }
    return payload;
}

有问题的错误是： （记录1至5与以下相同）

==15== 32 bytes in 4 blocks are definitely lost in loss record 5 of 7
==15==    at 0x4C2FB55: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==15==    by 0x400ECA: copy_string (projekti.c:80)
==15==    by 0x400F81: parse_one_line_params (projekti.c:106)
==15==    by 0x4010B6: deliver_payload (projekti.c:133)
==15==    by 0x4019A2: main (projekti.c:301)

第 301 行只是：

char **payload = deliver_payload(one_line, 3);

代码的编辑版本：

char **parse_one_line_params(const char *one_line, int param_count) {
    char *copy = copy_string(one_line);
    if (copy == NULL)
        return NULL;
    //copy_start is used to free the copy string in the end
    char *copy_start = copy;
    //It is assumed that one_line is of the form COMMAND SPACE ARGUMENTS
    //Move pointer to the first important character
    copy += 2;
    const char *separator = " ";
    char **content = malloc(sizeof(char *) * param_count);
    if (content == NULL) {
        free(copy_start);
        return NULL;
    }
    int occurrences = 0;
    char *delimiter_start;
    while ((delimiter_start = strstr(copy, separator)) != NULL) {
        delimiter_start[0] = '\0';
        char *sub_string = copy_string(copy);
        if (sub_string == NULL) {
            for (int i = 0; i < occurrences; i++) {
                free(content[i]);
            }
            free(copy_start);
            return NULL;
        }
        if (sub_string[0] != '\0') {
            int sub_len = strlen(sub_string);
            content[occurrences] = calloc(sub_len + 1, sizeof(char));
            strncpy(content[occurrences], sub_string, sub_len);
            free(sub_string);
        }
        //Since separator is of the length of one
        copy = delimiter_start + 1;
        occurrences++;
    }
    //param n - 1 will be assigned from the last portion of copy
     if (occurrences != param_count - 1) {
        printf("Too few parameters\nAborting\n");
        if (occurrences > 0) {
            for (int i = 0; i < occurrences; i++) {
                free(content[i]);
            }
        }
        free(content);
        return NULL;
    }
    int last_len = strlen(copy);
    if (last_len > 0 && copy[last_len - 1] == '\n')
        copy[last_len - 1] = '\0';
    content[occurrences] = calloc(last_len + 1, sizeof(char));
    strncpy(content[occurrences], copy, last_len);
    /* content[occurrences] = copy_string(copy); */
    free(copy_start);
    return content;
}

编辑 valgrind： （在完整输出中，有问题的行是 140 和 118，即 callocs）

==15== 13 bytes in 2 blocks are definitely lost in loss record 3 of 7
==15==    at 0x4C2FB55: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==15==    by 0x4011B0: parse_one_line_params (projekti.c:140)
==15==    by 0x401236: deliver_payload (projekti.c:153)
==15==    by 0x401B22: main (projekti.c:321)
==15== 
==15== 27 bytes in 6 blocks are definitely lost in loss record 4 of 7
==15==    at 0x4C2FB55: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==15==    by 0x401075: parse_one_line_params (projekti.c:118)
==15==    by 0x401236: deliver_payload (projekti.c:153)
==15==    by 0x401BBE: main (projekti.c:337)

最后一次编辑：我解决了这个特殊的问题：我忘了释放主函数中的参数列表，所以最后我叫错了树。

Answer 1

这里有内存泄漏

char **parse_one_line_params(const char *one_line, int param_count){
    char *copy = copy_string(one_line);
    if (copy == NULL)
        return NULL;

    /* ... */

    char **content = malloc(sizeof(char *) * param_count);
    if (content == NULL)
        return NULL;

如果malloc 为content 返回NULL，则您从函数返回而不释放copy 的内存。 malloc 极不可能失败，但如果您的其余代码以相同的模式编写，那么这就是泄漏的来源。

将每个malloc/strdup/calloc 与a free“平衡”是不够的。您必须跟踪分配内存的位置并释放它，以防您可以访问它的最后一个指针超出范围或被覆盖（感谢@Ctx）。

Answer 2

最后故障出在主函数中，我忘记释放新创建的参数列表。感谢@GSerg 和@datenwolf 指出我的代码中的其他错误。