This macro expands to a string constant that describes the date on which the preprocessor is being run. The string constant contains eleven characters and looks like "Feb 12 1996" . If the day of the month is less than 10, it is padded with a space on the left.
If GCC cannot determine the current date, it will emit a warning message (once per compilation) and __DATE__ will expand to "??? ?? ????" .
__TIME__
This macro expands to a string constant that describes the time at which the preprocessor is being run. The string constant contains eight characters and looks like "23:59:01" .
In my case, the compiler ran at 1pm but __TIME__ is set to 7am.