strftime doesn't work

Hello,

i'm using strftime() to format my date ouputs, e.g. the birthday. But
strftime() does'nt accept negative timestamps, which results from dates
before 1.1.1970. I need strftime because it formats the date according to
the language set with setlocale() using "%x". Does anyone know this problem
or has a workaround?

Thanks,
Thomas