Thread: multiple (ctime) struct tm* objects

I would like to store multiple "struct tm*" time data objects in a data class. These object would need to hold different times (lets say a start time, and an end time). But it seems like anytime I modify one of the objects they both change. How do I work around this?

(i can insert example code if needed)

Code:

time_t now;
struct tm *tm_now;
struct tm *tm_later;

now      = time ( NULL );
tm_now   = localtime ( &now );
tm_later = localtime ( &now );

tm_later->tm_hour = 12;

printf ( "%s", asctime ( tm_now ) );
printf ( "%s", asctime ( tm_later ) );

This isn't the actual code, but it is an example of what I am talking about. How can I make tm_now, and tm_later have different times?

Read the manual

Code:

NOTES
       The four functions acstime(), ctime(), gmtime() and localtime()  return
       a  pointer  to  static data and hence are not thread‐safe.

Since localtime() returns a pointer to static data, you can only use one at one, unless you save the result elsewhere

Code:

time_t now;
struct tm tm_now;
struct tm tm_later;

now      = time ( NULL );
tm_now   = *localtime ( &now );
tm_later = *localtime ( &now );

tm_later.tm_hour = 12;

printf ( "%s", asctime ( &tm_now ) );
printf ( "%s", asctime ( &tm_later ) );