[SOLVED] How to check if a variable is of "const" qualifier type in C?

Issue

Sample code to check

#include<stdio.h>

int main(void)
{
    const int i = 1;
    printf("Variable i is %s\n",
           __builtin_constant_p(i) ? "a const variable" : "not a const variable");
    return 0;
}

Output :

Variable i is not a const variable

Is __builtin_constant_p() not the right API to determine whether a variable is of type const or not?

Solution

You can use Generic selection (since C11):

#include <stdio.h> 

#define __is_constant_int(X) _Generic((&X), \
        const int *: "a const int", \
        int *:       "a non-const int")

int main(void)
{
    const int i = 1;
    printf("Variable i is %s\n", __is_constant_int(i));
    return 0;
}

Answered By - nalzok

Answer Checked By - David Goodson (WPSolving Volunteer)