Question

This code gives me warnings:

$ cat test.c
#include<stdio.h>
#include<time.h>

int main() {

    time_t t;
    scanf("%lld", &t);
    printf("%lld\n", t);
    return 0;
}
$ gcc test.c -o test
test.c: In function ‘main’:
test.c:7: warning: format ‘%lld’ expects type ‘long long int *’, but argument 2 has type ‘time_t *’
test.c:8: warning: format ‘%lld’ expects type ‘long long int’, but argument 2 has type ‘time_t’
$ 

Apart from the warnings, the code works as expected.

What should I do to not get the warnings on compilation (no compiler pragma tricks please)?

Answer 1

The exact type of time_t depends on your platform and OS. It’s still quite often 32 bit (either int or long), not 64, and some even use floats. The correct thing to do is to read into a known-size integer (either int or long long) and then assign the value to a time_t as a second step.