Question

What are bit fields? What is the use of bit fields in a structure declaration?

Answer 1

Answer:

A bit field is a data structure used in computer programming. It consists of a number of adjacent computer memory locations which have been allocated to hold a sequence of bits, stored so that any single bit or group of bits within the set can be addressed. A bit field is most commonly used to represent integral types of known, fixed bit-width.

In C, we can specify size (in bits) of structure and union members. The idea is to use memory efficiently when we know that the value of a field or group of fields will never exceed a limit or is withing a small range.

For example, consider the following declaration of date without use of bit fields.

#include <stdio.h>  

  // A simple representation of date  

struct date  

{  

  unsigned int d;  

  unsigned int m;  

  unsigned int y;  

};  

  int main()  

{  

  printf("Size of date is %d bytes\n", sizeof(struct date));  

  struct date dt = {31, 12, 2014};  

  printf("Date is %d/%d/%d", dt.d, dt.m, dt.y);  

}