Question

I can compile DLLs properly using mingw and do the exports/imports stuff. What I am looking for is defining the dll onload function properly as you would in MS VC products. Google didn’t turn up anything. Anyone have any ideas or a link to a tutorial?

Answer 1

Okay, so after some fiddling…it’s working. For anyone else that is having issues here it is. My issues weren’t related to compiling in instead of loading dynamically. It was a mash-up of a couple of tutorial/question/how-tos that got me to this point.

dll.c

#include <stdio.h>
#include <windows.h>
#include "dll.h"

//extern "C" BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD Reason, LPVOID LPV) {
//This one was only necessary if you were using a C++ compiler

BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved) {

    switch (fdwReason)
    {
        case DLL_PROCESS_ATTACH:
            // Code to run when the DLL is loaded
        printf ("Load working...\n");
            break;

        case DLL_PROCESS_DETACH:
            // Code to run when the DLL is freed
        printf ("Unload working...\n");
            break;

        case DLL_THREAD_ATTACH:
            // Code to run when a thread is created during the DLL's lifetime
        printf ("ThreadLoad working...\n");
            break;

        case DLL_THREAD_DETACH:
            // Code to run when a thread ends normally.
        printf ("ThreadUnload working...\n");
            break;
    }

    return TRUE;
} 

EXPORT void hello(void) {
    printf ("Hello\n");
}

dll.h

#ifndef DLL_H_
#define DLL_H_

#ifdef BUILD_DLL
/* DLL export */
#define EXPORT __declspec(dllexport)
#else
/* EXE import */
#define EXPORT __declspec(dllimport)
#endif

EXPORT void hello(void);

#endif /* DLL_H_ */

hello.c

#include <windows.h>
#include <stdio.h>

int main () {

    /*Typedef the hello function*/
    typedef void (*pfunc)();

    /*Windows handle*/
    HANDLE hdll;

    /*A pointer to a function*/
    pfunc hello;

    /*LoadLibrary*/
    hdll = LoadLibrary("message.dll");

    /*GetProcAddress*/
    hello = (pfunc)GetProcAddress(hdll, "hello");

    /*Call the function*/
    hello();
    return 0;
}

when compiled with

gcc -c -DBUILD_DLL dll.c
gcc -shared -o message.dll dll.o -Wl,--out-implib,libmessage.a
gcc -c hello.c
gcc -o hello.exe hello.o message.dll

produces the expected output of

Load working...
Hello
Unload working...