Return ISO 8601 timestamp

timestamp.c

/* -*- c-file-style: "k&r"; indent-tabs-mode: nil; -*- */
#include <stdio.h>
#include <stdlib.h>

#include <time.h>
 
/* returns a timestamp in the form of YYYY-mm-dd HH-MM.
 * buf needs to be able to hold 19+1 characters (incl. \0).
 * returns 0 on success -1 otherwise.
 */
int timestamp(char *buf)
{
     time_t ltime;
     struct tm *tm;
     
     buf[0] = '\0'; /* avoid undefined results */

     
     if (time(&ltime) == (time_t)-1) {
          return -1;
     }
     if ((tm = localtime(&ltime))==NULL) {
          return -1;
     }
     if (strftime(buf, 20, "%Y-%m-%dT%H:%M:%S", tm) != 19) {
         buf[0] = '\0'; /* avoid undefined results */
         return -1;
     }
     
     return 0;
}


int main(void)
{
     char buf[20];

     if (timestamp(buf) == 0) {
          printf("%s\n", buf);
     } else {
          printf("timestamp() failed\n");
     }
}