[SGVLUG] undefined reference to shared object

[Don Saxton]

I am compiling asterisk with app_rxfax, but at the link stage I get 
"undefined reference" for functions I know are in libspandsp.so.

I don't know how the linker confirms that the functions, etc are in the 
library.  Intuitively I think that the /usr/include/spandsp header files 
define the interface of the library, however that is not buying me much 
in trying to fix the problem..

Is it true that the linker needs those header files and is not finding them?
Can I add something to linker options to correct this?

Thanks