Allocate memory for char array pointer of struct inside function

Question

I was looking around for about one day on how to solve my problem. I find solutions for problems similar to mine but when I apply changes error : error: request for member 'mark' in something not a structure or union keeps showing.

What I have so far is a struct and I want to initialize it on a function call.

Edit my code:

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

try to avoid too many *s in your code,

was able to run it after making some changes, please refer to the ideone link in the next line.

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; 
    }
 }

Answer 2

Just replace

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

With

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

is a pointer wich is the address of the struct, so ... 是一个指针， 是该结构的地址，所以...

1) first you need to _st , and... _st ，然后...
2) second, with the you get, you point to the field mark ，指向字段标记

That's all !