Date with year, month and day equal to zero is considered illegal (otherwise it what be regarded as 30.11.1999, which would be strange behavior).
?php $lastday = mktime (0,0,0,3,0,2000); echo strftime ("Le dernier jour de F eacute;vrier 2000 est: %d", $lastday); $lastday = mktime (0,0,0,4,-31,2000); echo strftime ("Le dernier jour de F eacute;vrier 2000 est: %d", $lastday);?