Thread: Pointer to Structure not working

Hi,

In the following program, the structure "Root" is defined globally. Pointer to this structure gives compilation error.

Code:

#include<stdio.h>

typedef struct
{
int a;
float f;
}Root;


int main()
{
        Root *root, root_h;

        root_h.a=1;
        root_h.f=10.11;

        root = &root_h;

        printf("\n Values : \n root.a = %d \n root.f = %f \n", root_h->a, root_h->f);

        return 0;
}

The compilation error is:

error: invalid type argument of ‘->''

How to resolve this error?

Try with this one.
printf("\n Values : \n root.a = %d \n root.f = %f \n", root->a, root->f);

Ok. Thanks.

If the program is using a pointer to strutcure, why it gives error if value is assigned directly to struct elements, as follows?

Code:

#include<stdio.h>

typedef struct 
{
int a[2];
float f;
}Root;

int main()
{
	Root *root;

	root.a[0]=0;
	root.a[1]=1;
	root.f=10.11;

	printf("\n Values : \n root.a[0] = %d \n root.a[1] = %d \n root.f = %f \n", root.a[0], root.a[1], root.f);

	return 0;
}

The compilation error is:

# gcc -g ker_data.c -o ker_data
ker_data.c: In function ‘main’:
ker_data.c:13: error: request for member ‘a’ in something not a structure or union
ker_data.c:14: error: request for member ‘a’ in something not a structure or union
ker_data.c:15: error: request for member ‘f’ in something not a structure or union
ker_data.c:17: error: request for member ‘a’ in something not a structure or union
ker_data.c:17: error: request for member ‘a’ in something not a structure or union
ker_data.c:17: error: request for member ‘f’ in something not a structure or union

Why these errors? Because, if:

int *a;

we can use: a = 10;

But why not the same with struct?

Dont mess up with Object of a structure and pointer to a structure.
When you declare pointer to structure, it doesn't contain memory for the structure variables.