Test if strftime sets errno

strftime.c

#include <time.h>
#include <stdio.h>
#include <errno.h>

int main(int argc, char* argv[])
{
    time_t t = time(0);
    char mbstr[100] = { 0 };
    printf("errno: %d\n", errno);
    size_t s = strftime(mbstr, sizeof(mbstr), ((argc>1) ? argv[1] : "%c"), localtime(&t));
    if (s)
        printf("%s\n", mbstr);
    else
        printf("errno: %d\n", errno);
}