What is Structure Padding in C? - Examples

About Structure Padding in C

Structure padding is a concept in C that adds one or more empty bytes between the memory addresses to align the data in memory.

Let's first understand the structure padding in C

Syntax:

struct student  

{  

  char a; // 1 byte  

  char b; // 1 byte  

  int c; // 4 bytes   

}  

Examples of Structure Padding in C

1) Example

Code:

//include basic C library files

#include <stdio.h>

//including string data member in C

#include <string.h>

//creating first structure

struct first_structure

{

int rollNo1, rollNo2;

char firstName;

char character;

float salary;

};

//creating second structure

struct second_structure

{

int rollNo1;

char firstName;

int rollNo2;

char character;

float salary;

};

//main method to run the C application

int main()

{

//taking first structure reference

struct first_structure s1;

//taking second structure reference

struct second_structure s2;

//displaying first_structure and second_structure output

printf("===================FIRST STRUCTURE===============================\n");

printf("size of first_structure in bytes : %d\n",sizeof(s1));

printf ( "\n   Address of rollNo1        = %u",&s1.rollNo1 );

printf ( "\n   Address of rollNo2        = %u",&s1.rollNo2 );

printf ( "\n   Address of firstName       = %u",&s1.firstName );

printf ( "\n   Address of character          = %u",&s1.character);

printf ( "\n   Address of salary = %u",&s1.salary);

printf("\n===================SECOND STRUCTURE===============================\n");

printf("size of second_structure in bytes : %d\n",sizeof(s2));

printf ( "\n   Address of rollNo1        = %u",&s2.rollNo1 );

printf ( "\n   Address of rollNo2        = %u",&s2.rollNo2 );

printf ( "\n   Address of firstName       = %u",&s2.firstName );

printf ( "\n   Address of character          = %u",&s2.character);

printf ( "\n   Address of salary = %u",&s2.salary);

getchar();

return 0;

}

Output:

2) Example

Code:

//include basic C library files

#include<stdio.h>

//including string data member in C

#include <string.h>

//creating first structure

struct employee

{

char first_name[40];

char last_name[30];

};

//main method to run the C application

int main()

{

//taking first structure reference

struct employee e;

printf("Enter your first name:");

scanf("%s", &e.first_name);

printf("Enter your last name:");

scanf("%s",&e.last_name);

printf("First Name of Employee is :%s\n",e.first_name);

printf("Last Name of Employee is :%s\n", e.last_name);

//displaying output

printf("==================1ST STRUCTURE=========================\n");

printf("size of employee in bytes : %d\n",sizeof(e));

printf ( "\n   Address of first_name        = %u",&e.first_name);

printf ( "\n   Address of last_name        = %u",&e.last_name );

return 0;

}

Output:

3) Example

Overcome Structure padding problem in C

Code:

//include basic C library files

#include <stdio.h>

//including string data member in C

#include <string.h>

#pragma pack(1)

//creating first structure

struct first_structure

{

int rollNo1, rollNo2;

char firstName;

char character;

float salary;

};

//creating second structure

struct second_structure

{

int rollNo1;

char firstName;

int rollNo2;

char character;

float salary;

};

//main method to run the C application

int main()

{

//taking first structure reference

struct first_structure s1;

//taking second structure reference

struct second_structure s2;

//displaying first_structure and second_structure output

printf("===================FIRST STRUCTURE===============================\n");

printf("size of first_structure in bytes : %d\n",sizeof(s1));

printf ( "\n   Address of rollNo1        = %u",&s1.rollNo1 );

printf ( "\n   Address of rollNo2        = %u",&s1.rollNo2 );

printf ( "\n   Address of firstName       = %u",&s1.firstName );

printf ( "\n   Address of character          = %u",&s1.character);

printf ( "\n   Address of salary = %u",&s1.salary);

printf("\n===================SECOND STRUCTURE===============================\n");

printf("size of second_structure in bytes : %d\n",sizeof(s2));

printf ( "\n   Address of rollNo1        = %u",&s2.rollNo1 );

printf ( "\n   Address of rollNo2        = %u",&s2.rollNo2 );

printf ( "\n   Address of firstName       = %u",&s2.firstName );

printf ( "\n   Address of character          = %u",&s2.character);

printf ( "\n   Address of salary = %u",&s2.salary);

getchar();

return 0;

}

Output: