Using C string function within flex files

[nodo8]

Hello guys!!
I´m a spaniard student and I´m trying to do an xml processor using flex
and yacc. But now I have a hard problem to solve.
Every time a use a string function (i.e. strcpy(), strcmp(), etc.), the
program breaks down. I mean, I can compile with flex, I can compile with
yacc, and also I can compile with the C compiler (in this case bcc32,
the C compiler of Buirder C++), but when I execute the exe file, the
program fail when it try to call a string function.

Do anybody have any idea about this problem? I know is difficult to work
with strings but this is ridiculous.

Thanks to everybody who can help me.