What are the default values of static variables in C? (original) (raw)

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).