输入数据到结构成员是一个指针

Question

#include<stdio.h>
#include<stdlib.h>
struct test
{
    int x;
    int *y;
};

main()
{
    struct test *a;
    a = malloc(sizeof(struct test));

    a->x =10;
    a->y = 12;
    printf("%d %d", a->x,a->y);
}

I get the o/p but there is a warning

 warning: assignment makes pointer from integer without a cast

and

 warning: format ‘%d’ expects type ‘int’, but argument 3 has type ‘int *’

how to input a value to *y in struct test

Answer 1

To access, you need to dereference the pointer returned by the expression a->y to maniputlate the pointed at value. To do this, use the unary * operator:

You also need to allocate memory for y to make sure it points at something:

a->y = malloc(sizeof(int));
...
*(a->y) = 12;
...
printf("%d %d", a->x,*(a->y));

And be sure to free malloc'd data in the reverse order it was malloc'd

free(a->y);
free(a);