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cstatic

Static variable inside of a function in C

What will be printed out? 6 6 or 6 7? And why?

void foo()
{
    static int x = 5;
    x++;
    printf("%d", x);
}

int main()
{
    foo();
    foo();
    return 0;
}
Solution

  • There are two issues here, lifetime and scope.

    The scope of variable is where the variable name can be seen. Here, x is visible only inside function foo().

    The lifetime of a variable is the period over which it exists. If x were defined without the keyword static, the lifetime would be from the entry into foo() to the return from foo(); so it would be re-initialized to 5 on every call.

    The keyword static acts to extend the lifetime of a variable to the lifetime of the programme; e.g. initialization occurs once and once only and then the variable retains its value - whatever it has come to be - over all future calls to foo().