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无法从结构成员变量中释放内存

转载 作者：太空宇宙 更新时间：2023-11-04 05:33:58 27 4
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我在 C 中对结构变量调用 free 后，检查该变量是否为 NULL，它告诉我它不是 NULL。所以 free 没有用？我的代码:

struct main_struct {
    struct my_file *file;
};

struct my_file {
    char *host;
    int port; // this cannot be malloc'ed and free'ed
};

struct my_file* read_file() {
    FILE *f;
    struct my_file *file;

    //open FILE for reading..

    file = malloc(sizeof(struct my_file)); //allocate memory for my_file struct
    memset(file, 0, sizeof(struct my_file));

    // while loop to read file content..
    // in the loop:
        char *value = line;
        file->host = malloc(sizeof(char) * strlen(value)); //allocate memory for host member variable
        strncpy(file->host, value, strlen(value)); //assign value to host variable

    return file;
}

int main() {
    struct main_struct *mstr;
    mstr = malloc(sizeof(struct main_struct)); //allocate memory to main_struct
    memset(mstr, 0, sizeof(struct main_struct));

    mstr->my_file = read_file(); //call to read file, allocate mem for my_file struct and the 'host' member variable

    // some code

    // call free here:
    if(mstr->my_file->host != NULL) {
        free(mstr->my_file->host);
    }
    // check if mem has been freed:
    if(mstr->my_file->host == NULL) {
        printf("mstr->my_file->host is NULL, good.\n");
    } else {
        printf("mstr->my_file->host is NOT NULL, bad.\n"); // I see this.
    }

    // I also try to free mstr->my_file:
    if(mstr->my_file != NULL) {
        free(mstr->my_file);
    }
    // check if mem has been freed:
    if(mstr->my_file == NULL) {
        printf("mstr->my_file is NULL, good.\n");
    } else {
        printf("mstr->my_file is NOT NULL, bad.\n"); // I see this.
    }

    // and also mstr itself..
}

我是否正确使用了 free 函数，因为我看到过这样调用 free 的示例:free(&mystruct->myfile->host); 通过发送指向 free 的指针地址。但我认为我现在调用免费电话的方式是正确的..？

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