generate a date string in HTTP response date format in C

Use strftime(), declared in <time.h>.

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

int main(void) {
  char buf[1000];
  time_t now = time(0);
  struct tm tm = *gmtime(&now);
  strftime(buf, sizeof buf, "%a, %d %b %Y %H:%M:%S %Z", &tm);
  printf("Time is: [%s]\n", buf);
  return 0;
}

See the code "running" at codepad.