C Structure Pointers

C Structure Pointers

The way We can have a pointer pointing to an int, or a pointer pointing to a float similarly we can have a pointer pointing to a struct user defined type. such pointers are called as structure pointers.

In programming, we usally deal with collection of ints, chars and floats rather than isolated entities.

Example an entity book is a collection of things like a title, an author, total pages, date of publication and price etc..

Structure is user defined data type which combines dissimilar data types into an entity.

Structure Pointers C program

This c program shows how to use the structure pointers.

Declared ptr structure pointer and gets the address of structure variable 'b1' of structure 'book'.

Prints the structure variable b1 enitire elements using structure variable b1 and also using structure pointer ptr and results shows the same.

#include<stdio.h>                                                          
                                                                                
struct book                                                                     
{                                                                               
  int id;                                                                       
  char *title;                                                                  
  char *author;                                                                 
  float price;                                                                  
};                                                                              
                                                                                
void main()                                                                     
{                                                                               
                                                                                
  struct book  b1 = {1, "book1", "author1", 20.5};                              
  struct book *ptr;                                                             
                                                                                
  ptr = &b1;                                                                    
                                                                                
  printf("\nbook id\ttitle \t auther \t price \n");                             
  printf("%d\t%s\t%s \t%f\n", b1.id, b1.title, b1.author, b1.price);            
  printf("%d\t%s\t%s \t%f\n", ptr->id, ptr->title, ptr->author, ptr->price);    
}  

Output:

$ cc structure.c
$ ./a.out 

book id	title 	 auther 	 price 
1	book1	author1 	20.500000
1	book1	author1 	20.500000

We will update one of the element 'title' of the structure variable 'b1' using structure pointer 'ptr' and will check the results again shows same or different. Obiously will be the same result.

#include<stdio.h>                                                                   
                                                                                
struct book                                                                     
{                                                                               
  int id;                                                                       
  char *title;                                                                  
  char *author;                                                                 
  float price;                                                                  
};                                                                              
                                                                                
void main()                                                                     
{                                                                               
                                                                                
  struct book  b1 = {1, "book1", "author1", 20.5};                              
  struct book *ptr;                                                             
                                                                                
  ptr = &b1;                                                                    
  ptr->title = "book2";                                                         
  printf("\nbook id\ttitle \t auther \t price \n");                             
  printf("%d\t%s\t%s \t%f\n", b1.id, b1.title, b1.author, b1.price);            
  printf("%d\t%s\t%s \t%f\n", ptr->id, ptr->title, ptr->author, ptr->price);    
} 

Output:

$ cc structure.c
$ ./a.out 

book id	title 	 auther 	 price 
1	book2	author1 	20.500000
1	book2	author1 	20.500000