学生结构中的 C 内存分配不起作用

Question

我必须在下面的 internal.h 中实现这些函数:

#ifndef STUDENT_INTERNAL_H
#define STUDENT_INTERNAL_H

#include "student.h"

/** Allocate memory for a new @ref student object. */
struct student *student_alloc(void);

/*** Initialize an already-allocated @ref student object.
* @returns   NULL on failure but does not free the memory
*/

struct student *student_init(struct student *, const char *name, size_t namelen, 
                             struct student_id, student_complete);

#endif /* STUDENT_INTERNAL_H */

这是我到目前为止所拥有的，但我很困惑并且它不起作用:

#include <sys/types.h>
#include "common.h"
#include "student.h"
#include "transcript.h"
#include "internal.h"

/**
* Initialize an already-allocated @ref student object.
* @returns   NULL on failure but does not free the memory
*/
struct student *student_init(struct student *student, const char *name, size_t namelen,
                             struct student_id stud_id, student_complete stud_complete) {

    struct student *initialized_student;

    name = malloc(sizeof(namelen));
    initialized_student = malloc(sizeof (student));

    if (student_alloc()) {
        initialized_student->s_name = name;
        initialized_student->s_id = stud_id;
        initialized_student->s_complete = stud_complete;

        return initialized_student;
    } else {
        return 0;
    }
}

stud_complete 这里是一个函数指针，它在不同的头文件 student.h 中声明，如 typedef int (*student_complete)(struct Student *);

Answer 1

API 令人困惑:

什么是namelen？

• 是学生姓名name开头前缀的长度吗？在这种情况下，您应该为空终止符分配一个额外的字节并适本地复制名称。
• 这是学生姓名的最大长度吗？同样，如果这是长度而不是大小，则您需要一个额外的字节作为空终止符。
• 无论如何，sizeof(namelen) 都是不合适的。

student_alloc() 做什么？

同样，传递给 malloc() 来分配 student 结构的大小应该是 struct Student 的大小，或更可靠的是目标指针指向的类型。

这是更正后的版本:

struct student *student_init(struct student *student, const char *name, size_t namelen,
                             struct student_id stud_id, student_complete stud_complete) {

    struct student *initialized_student = malloc(sizeof(*initialized_student));
    char *s_name = calloc(namelen + 1);

    if (initialized_student && s_name && student_alloc()) {
        strncat(s_name, name, namelen);
        initialized_student->s_name = s_name;
        initialized_student->s_id = stud_id;
        initialized_student->s_complete = stud_complete;
        return initialized_student;
    } else {
        free(initialized_student);
        free(s_name);
        return 0;
    }
}