Get Unix timestamp from SQL timestamp through libpq

I know I can convert SQL timestamp to unix timestamp, using the following way.

SELECT extract(epoch FROM now());

Now, I have a stored procedure function, which will directly return a table row to the caller. One of the row field is "timestamp" type.

In my application, I am using libpq. I wish to use libpq functions (or any c/c++ function), to convert "2010-01-11 13:10:55.283" into unix timestamp. Off course, I can create another stored procedure named

SQLTimestamp2UnixTimestamp
SELECT extract(epoch FROM $1);

But I just wish to accomplish this task with a single c/c++ function call, without involving stored procedure.

Any suggestion? Thanks!

Thanks and Regards
Yan Cheng CHEOK