C++ undefined reference to defined function

Question

I cannot figure out why this is not working. I will put up all three of my files and possibly someone can tell me why it is throwing this error. I am using g++ to compile the

Answer 1

Though previous posters covered your particular error, you can get 'Undefined reference' linker errors when attempting to compile C code with g++, if you don't tell the compiler to use C linkage.

For example you should do this in your C header files:

extern "C" {

...

void myfunc(int param);

...

}

To make 'myfunc' available in C++ programs.

If you still also want to use this from C, wrap the extern "C" { and } in #ifdef __cplusplus preprocessor conditionals, like

#ifdef __cplusplus
extern "C" {
#endif

This way, the extern block will just be “skipped” when using a C compiler.