Structure Pointer in C Programming

Pointer to structure

A pointer to a structure can be used by the '&' operator.

Take the struct student and define the s1 variable of type struct student
struct student s1;

&s1 will give the starting address of the structure.

The variable and the pointer variable can be combined and declared as follows:

struct student
{
.
.
}
s1, *ptr_stud;
ptr_stud = &s1;

Accessing members of structure which has a pointer is
ptvar → member

Where,
ptvar is a structure type pointer variable
→ is comparable to the '.' operator.

The '.' operator requires a structure variable whereas a → requires a structure pointer on its left side.

Following table will tell us how the members of structures are accessed by using the structure pointer:

Member	Structure variable	Structure pointer
Ordinary variable	var.member s1.roll_no	ptvar → member (ptr_stud → roll_no) (*ptr_stud). roll_no
Array	var.member[expression] s1. name	ptvar → member[expression] ptr_stud → name (*ptr_emp).name
Nested structure	var.member.submember s1.n.last_name	ptrvar → member.submember ptr_stud → n.last_name (*ptr_stud).n.last_name

Passing the structures as parameters

A structure can be passed as a parameter to a function. This can be done by using three methods.

1. Individual structure members
As the members of the structures are individual entities they can be passed and returned from the functions.

Example : The coordinates of a point is returned

#include <stdio.h>
typedef struct
{
    int a;
    int b;
}point;

void d(int, int);
void main()
{
    point p1 = {5,10};
    d(p1.a, p1.b);
}

void d(int x, int y)
{
    printf("The coordinates are : %d %d",x,y);
}

Output:
The coordinates are : 5 10

2. Passing structure as a whole
An entire structure can be passed as an argument. It is passed by using the call by value method.

Syntax:
struct struct_name func_name (struct struct_name struct_var);

Note: The above syntax can vary as per the needs.

Example : Passing a structure to a function by using the call by value method

#include <stdio.h>
typedef struct
{
    int a;
    int b;
}point;

void d(point);
void main()
{
    point p1 = {15,20};
    d(p1);
}

void d(point p)
{
    printf("%d %d",p.a,p.b);
}

Output:
15 20

3. Passing pointer to structure

When large structures are required for passing a function using the call by value method is inefficient. Instead it can be done by using pointers.
It is common for creating a pointer to structure.
A pointer to a structure is not a structure itself but a variable which holds the address of the structure.

Syntax

struct struct_name
{
     member 1;
     member 2;
     .
     .
     member n;
}*ptr;

OR

struct struct_name *ptr;

Example:
struct student *ptr_stud, stud;

After this we need to assign an address of the stud to the pointer.

Hence, we will write
ptr_stud = &stud;

For accessing the members we will write
(*ptr_stud).fees

The above statement can also be written in the following format:
ptr_stud → fees = 50000;

It is more easier to work with this statement.