C Programming Structure and Pointer

Pointers can be accessed along with structures. A pointer variable of structure can be created as below:

struct name {
    member1;
    member2;
    .
    .
};
-------- Inside function -------
struct name *ptr;

Here, the pointer variable of type struct name is created.

Structure's member through pointer can be used in two ways:

  1. Referencing pointer to another address to access memory
  2. Using dynamic memory allocation

Consider an example to access structure's member through pointer.

#include <stdio.h>
struct name{
   int a;
   float b;
};
int main(){
    struct name *ptr,p;
    ptr=&p;            /* Referencing pointer to memory address of p */
    printf("Enter integer: ");
    scanf("%d",&(*ptr).a);
    printf("Enter number: ");
    scanf("%f",&(*ptr).b);
    printf("Displaying: ");
    printf("%d%f",(*ptr).a,(*ptr).b);
    return 0;
}

In this example, the pointer variable of type struct name is referenced to the address of p. Then, only the structure member through pointer can can accessed.

Structure pointer member can also be accessed using -> operator.

(*ptr).a is same as ptr->a
(*ptr).b is same as ptr->b

Accessing structure member through pointer using dynamic memory allocation

To access structure member using pointers, memory can be allocated dynamically using malloc() function defined under "stdlib.h" header file.

Syntax to use malloc()

ptr=(cast-type*)malloc(byte-size)

Example to use structure's member through pointer using malloc() function.

#include <stdio.h>
#include<stdlib.h>
struct name {
   int a;
   float b;
   char c[30];
};
int main(){
   struct name *ptr;
   int i,n;
   printf("Enter n: ");
   scanf("%d",&n);
   ptr=(struct name*)malloc(n*sizeof(struct name));
/* Above statement allocates the memory for n structures with pointer ptr pointing to base address */
   for(i=0;i<n;++i){
       printf("Enter string, integer and floating number  respectively:\n");
       scanf("%s%d%f",&(ptr+i)->c,&(ptr+i)->a,&(ptr+i)->b);
   }
   printf("Displaying Infromation:\n");
   for(i=0;i<n;++i)
       printf("%s\t%d\t%.2f\n",(ptr+i)->c,(ptr+i)->a,(ptr+i)->b);
   return 0;
}

Output

Enter n: 2
Enter string, integer and floating number  respectively:
Programming
2
3.2
Enter string, integer and floating number  respectively:
Structure
6
2.3
Displaying Information
Programming      2      3.20
Structure      6      2.30