What are the default values of static variables in C?

Last Updated : 14 Apr, 2023

In C, if an object that has static storage duration is not initialized explicitly, then: — if it has pointer type, it is initialized to a NULL pointer; — if it has an arithmetic type, it is initialized to (positive or unsigned) zero; — if it is an aggregate, every member is initialized (recursively) according to these rules; — if it is a union, the first named member is initialized (recursively) according to these rules. For example, following program prints: Value of g = 0 Value of gs = 0 Value of s = 0 

Example no 1

C 
#include <stdio.h>
int g; // g = 0, global objects have static storage duration
static int gs; // gs = 0, global static objects have static
               // storage duration
int main()
{
    static int s; // s = 0, static objects have static
                  // storage duration
    printf("Value of g = %d", g);
    printf("\nValue of gs = %d", gs);
    printf("\nValue of s = %d", s);

    getchar();
    return 0;
}

Output
Value of g = 0
Value of gs = 0
Value of s = 0

Example no 2 

C 
#include <stdio.h>

void print_static_vars(void)
{
    static int i = 0;
    static float f = 0.0;
    static char c = '\0';

    i++;
    f += 0.1;
    c++;

    printf("i = %d, f = %f, c = %c\n", i, f, c);
}

int main()
{
    print_static_vars();
    print_static_vars();
    print_static_vars();

    return 0;
}

Output

i = 1, f = 0.100000, c = ☺
i = 2, f = 0.200000, c = ☻     
i = 3, f = 0.300000, c = ♥

Explanation 

  • In this program, a function print_static_vars is declared that contains three static variables: i, f, and c. The function increments each of these variables and then prints their values.
  • The main function calls the print_static_vars function three times. Since the variables are static, their values persist between calls, and their values are updated each time the function is called.
  • As you can see, the default value of a static integer variable is 0, the default value of a static float variable is 0.0, and the default value of a static character variable is \0 (the null character).
Comment

Explore