C :: How To Share Imported DLL Functions Between Source Files

In general, my problem is that I've been trying to reorganize the project I and my group are working on into separate project files. Everything was working perfectly fine before, but now I'm facing the wrath of undefined reference errors when I try to call my DLL functions.

I have them declared and included in the central header file here :

Code:

/* DLL functions */
typedef void ( * t_wait )( int milliseconds, const int frames_per_seconds );
typedef clock_t ( * ft_timer )( int command, t_timer * timer_object ); /* clock_t is usually defined as long */
typedef void ( * t_SDL_errorexit )( const char * message );
typedef SDL_Surface * ( * t_load_image )( char * image_path, unsigned is_transparent );

[Code]...

Then I have them imported here :

Code:
/* ******************************************************** */
/* ********* win_error( char *, bool ) ********* */
/* ******************************************************** */
/* - Displays a GUI for a windows specific error message, */
/* pass true to it to have it exit the program, pass false */
/* to have it continue */
/* ******************************************************** */
extern void win_error( char * message, bool is_exit )
{
/* Note : win_error uses the Win32 Api */
/* ********************************** */
char buffer[BUFSIZ] = { 0 }; /*

[code]...

This doesn't work, as my compiler sees it that I am trying to call invalid functions, whereas I have made sure to import the functions before calling. Obviously my compiler can't tell that, and is trying to protect me from calling them.

The source files are compiled as C++, but I'm using C-style code instead of true C++ code.

Obviously I'm using Windows style DLL linking, but if the only ways to share imported functions are non-standard, only post ways that will work on as low as Windows XP.

I have tried to statically link them before, but that led to a problem that I posted a while back. Which led me to dynamically linking, which was problem-free until I separated my code into separate files.