How to compile c program as dll

Question

I finished working on my Checkers game engine and about to make it CheckerBoard (http://www.fierz.ch/cbdeveloper.php) compatible, and it states that.

CheckerBoard expects your engine to be compiled as a dll and to be in the working directory of checkerboard.exe - or in the path. An engine must support 2 required functions. ..., you must provide 2 more functions for multi-version support. The calling convention for all functions is __stdcall().

Required Functions

The current CheckerBoard API (version 2) requires the following 2 functions:
int WINAPI getmove(int board[8][8], int color, double maxtime, char str[1024], int *playnow, int info, int moreinfo, struct CBmove *move);
int WINAPI enginecommand(char command[256], char reply[1024]);

my engine includes the two above functions, i've got everything setup (the code) but i'm having troubles compiling it as dll, heres what i tried (using gcc)

gcc -c engine.c
gcc -shared -o engine.dll engine.o

it creates the dll as expected but the dll doesn't export any of the functions (as expected).

I used the Dependency walker program to scan the engine.dll file, and it shows that the dll exports the functions

_getmove@28
_enginecommand@20

i scanned one of the engines in the CheckerBoard directory and i found that they export the following functions:

getmove
enginecommand

i cant figure out why the dll i created exports differently, maybe its got something to do with the WINAPI ?.

Any ideas ?

here's what it looks like

#define EXPORT __declspec(dllexport)

EXPORT int WINAPI getmove(int b[8][8], int color, double time, char str[1024], int *playnow, int info, int unused, struct CBmove *cbmove){
    // ....
    return 0;
}


EXPORT int WINAPI enginecommand (char str[256], char reply[1024]){
    // ...
    return 0;
}

i need both functions to be exported through the dll.

Please edit your question by giving some minimal reproducible example, or at least by showing the relevant code (and declarations) in your engine.c; show the lines declaring and defining getmove etc — Basile Starynkevitch

Basile Starynkevitch Basile Starynkevitch · Accepted Answer · 2017-11-26T19:40:14

You probably need to annotate (the declaration of) these exported functions with Windows function attributes like __attribute__((dllexport)); I recommend having a declaration like

extern WINAPI getmove(int b[8][8], int color, double time, 
                      char str[1024], int *playnow, int info, 
                      int unused, struct CBmove *cbmove) 
       __attribute__((dllexport));

before that function's definition.

You may need to compile your source as position independent code (on Linux it is nearly required with -fPIC, for Windows DLL you need to check your documentation).

So try to compile with gcc -Wall -O -g -fPIC -shared engine.c -o engine.dll

See also this related question (and answers there).

^{PS. I never used Windows (only Unix since 1987 and Linux since 1993). I recommend reading Levine's Linkers and loaders book}

How to compile c program as dll

1 Answers