I was just going to write what ta0kira wrote. The GNU
date command is awesome. Anyway, in C, you can do
Code:
#include <stdio.h>
#include <time.h>
int main(void)
{
time_t now, then;
struct tm *split;
/* Get the current time */
now = time(NULL);
/* Convert the time to broken-down format */
split = localtime(&now);
/* Substract two days -- it is okay to go out of valid range */
split->tm_mday -= 2;
/* Renormalize the broken-down format, and return the time then. */
then = mktime(split);
printf("Two days ago was %04d-%02d-%02d, or %s\n",
split->tm_year + 1900, split->tm_mon + 1, split->tm_mday,
ctime(&then));
return 0;
}
This uses the local time as a basis. If you need UTC, use
gmtime instead of
locatime.
The call to
mktime both normalizes the split date, and returns the resulting time in the base
time_t format, seconds since epoch. See the
ctime, localtime, and mktime man page for details. This is in the POSIX standard, and should work as-is on all sane operating systems.
It shouldn't be too difficult to add parameter parsing to the above, to get exactly what you need.
Nominal Animal
