/* cc -Wall -g strp.c -o strp */
#define _XOPEN_SOURCE
#include <time.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
    struct tm tm;
    char *c;

    c = strptime(argv[1], "%s", &tm);

    printf("%s", asctime(&tm));

    return 0;
}

##</code><code>##

$ TZ=MSK ./strp 1415998800
Fri Nov 14 21:00:00 2014