I need to add seconds to a date. For example, if I have a date such as 2009127000000, I need to add the seconds to this date. Another example, add 50 seconds to 20091231235957.
Is this possible in C?
In POSIX a time_t
value is specified to be seconds, however that's not guaranteed by the C standard, so it might not be true on non-POSIX systems. It commonly is (in fact, I'm not sure how often it isn't a value representing seconds).
Here's an example of adding time values that doesn't assume a time_t
represents seconds using the standard library facilities, which are really not particularly great for manipulating time:
#include <time.h>
#include <stdio.h>
int main()
{
time_t now = time( NULL);
struct tm now_tm = *localtime( &now);
struct tm then_tm = now_tm;
then_tm.tm_sec += 50; // add 50 seconds to the time
mktime( &then_tm); // normalize it
printf( "%s\n", asctime( &now_tm));
printf( "%s\n", asctime( &then_tm));
return 0;
}
Parsing your time string into an appropriate struct tm
variable is left as an exercise. The strftime()
function can be used to format a new one (and the POSIX strptime()
function can help with the parsing).
Use types and functions from <time.h>
.
time_t now = time(0);
time_t now_plus_50_seconds = now + 50;
time_t now_plus_2_hours = now + 7200;
<time.h>
declares functions that deal with time_t
and struct tm
types. These functions can do all you want.
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