I have a function func.h that I am trying to compile into a shared library so that it can be linked to in other functions. I run the command

g++ -fPIC -shared /obj/func.o -o /lib/libFunction.so

which is fine, and then when I try to compile my function main.cpp (which has a line in it, #include "func.h"), and link it to this library, using the command

g++ -I/include -g -lm -fPIC -Wall -lFunction main.cpp -o /bin/main

I get the error:

In function 'main':
main.cpp:51: undefined reference to 'func(args)'

I have double checked to make sure that main has a #include line with the func.h header in it, and that the arguments listed in the error for the function func are consistent with what is being attempted, but everything seems fine. Am I somehow linking incorrectly or missing an important flag? Thanks in advance for your help.

Is "func()" also implemented? That is, do you have more than just its prototype?

func() is implemented, but I noticed in the header it is implemented as

func( const vector< double > &input )

whereas in the cpp file it is given as

func( vector< double > &input )

I didn't even think to check this - and now it compiles. Thanks for your help!

Its sometimes easy to overlook things like this, and assume its a more complicated issue at hand. Therefore, its always good to check the prototype against its implementation (or do a copy/paste when you implement the prototype to make sure its the same). Good to see you got it working now.