undefined symbol with flex/bison

Hi,
I am trying to write two parsers using bison/flex.  I can get the parsers to work independantly but i need both of them in the same executable.  So i used the -P and -p options for flex and bison respectively, giving them "aef".  Everything compiles fine but during runtime i get  

symbol lookup error: <lib name>: undefined symbol: aefin

i changed the declarations to

extern "C" FILE* aefin;
extern "C" int aeflex();
extern "C" void aeferror(const char*);
extern int aefparse(void*);

instead of yyXXX but i still get the undefined symbol error.

Any help would be greatly appreciated.