how to debug functions called from other classes

[Grazia Russo-Lassner]

Hi,

the function BuildVcb is where the error message of my code comes from:

line50 : parser->BuildVcb(arg1, arg2);

But BuildVcb is actually a function implemented in a separate class.
Thus, when I use the gdb commands (run, next, step, where, etc.) I end up 
executing the function without being able to go step by step inside BuildVcb.
What gdb commands should I use ?
I would very much appreciate if someone could help, I am a novice in gdb.

thank you,

grazia