为函数内部结构的char数组指针分配内存

Question

我花了大约一天的时间寻找如何解决我的问题。我找到了类似于我的问题的解决方案，但当我应用更改错误:error: request for member 'mark' in something not a structure or union一直显示。

到目前为止，我有一个struct，我想在函数调用中初始化它。

编辑代码:

typedef struct student * Student;
struct student {
    char *mark; /* or array[2] like array[0] = 'A' , array[1] = 'B' */
    int age;
    int weight;
};
typedef enum{
    MEMORY_GOOD,
    MEMORY_BAD} Status; 
int main(int argc, char* argv[]) {
    int status = 0; 
    Student john  

    /* Function  call to allocate memory*/
    status = initMemory(&john);
    return(0);
}

Status initMemory(Student *_st){
     _st =  malloc(sizeof(Student));

    printf("Storage size for student : %d n", sizeof(_st));
    if(_st == NULL)
    {
        return MEMORY_BAD;
    }   
    _st->mark = malloc(2*sizeof(char)); /* error: request for member 'mark' in something not a structure or union */
    return MEMORY_GOOD; 
}

Answer 1

直接替换

_st->mark = malloc(2 * sizeof(char));

(*_st)->mark = malloc(2 * sizeof(char));

_st是一个指针，其中内容是结构体的地址，所以…

1)首先需要对解引用_st，然后…
2)第二，用你得到的值指向字段标记

Answer 2

尽量避免代码中出现太多*，

在做了一些更改后能够运行它，请参阅下一行的ideone链接。

http://ideone.com/Ow2D2m

#include<stdio.h>
#include<stdlib.h>
typedef struct student* Student; // taking Student as pointer to Struct
int initMemory(Student );
struct student {
char* mark; /* or array[2] like array[0] = 'A' , array[1] = 'B' */
int age;
int weight;
};
typedef enum{
    MEMORY_GOOD,
    MEMORY_BAD} Status; 
int main(int argc, char* argv[]) {
    Status status;
    Student john;  /* Pointer to struct */
  /* Function  call to allocate memory*/
    status = initMemory(john);
    printf("got status code %d",status);
}
int initMemory(Student _st){
     _st =  (Student)malloc(sizeof(Student));
    printf("Storage size for student : %d n", sizeof(_st));
    if(_st == NULL)
    {
        return MEMORY_BAD;
    }   else {
        char* _tmp = malloc(2*sizeof(char)); /* error: request for member     'mark' in something not a structure or union */
    _st->mark = _tmp;
    return MEMORY_GOOD; 
    }
 }