date of week in month

[roger5089]

Dear all
what's c++ function name is can use to know the
date of week in month
for example
today is 2007-12-19
this the day = 19 in this month is 3 weeks pass in this month
how if the day = 25 is next week in this month .
my question is does any idea i can use code to calculate which day of week in each month?

thank's