How to declare DLL in user32.dll (aka stdcall?) fashion? - c

Question

I have a third party application that allows you to call C functions from DLL files. Provided sample to this app shows you can call MessageBoxW from user32.dll. It also allows you to call C functions from your DLL files.
I've did a DLL from a file.h file like this:
_declspec (dllexport) void example(int);
and file.c like this:
#include <stdio.h>
#include "file.h"
_declspec (dllexport) void example(int s1)
{
printf("dsa");
}
And compile it with C/C++ Compiler Version 15 from Windows SDK like this:
cl file.c /DLL /LD
And i get proper compilation with DLL file. In DLL functions examiner I see my function. I drop this file into System32 folder and call it from this third party application.
Application finds the file, but is unable to find the function.
I think the cause of the problem is that i declare (or compile) my DLL in other fashion/way/standard that Windows libraries (like user32.dll) because user32.dll works fine.
I've found that the third party app uses this kind of calling functions in DLL:
winapi_abi Used for calling Windows system functions. These are
declared as stdcall on Windows, but do not have mangled names.
So my question is: how to prepare and compile DLL file in the user32.dll fashion (stdcall?) so it will work with third party app?

Answer 1

The easy answer is:
__declspec(dllexport) void __stdcall example(int);
And the same in the implementation, of course.
If you look into windows.h and friends you'll see:
#define WINUSERAPI __declspec(dllexport)
#define WINAPI __stdcall
And then:
WINUSERAPI int WINAPI MessageBoxW(HWND,LPCWSTR,LPCWSTR,UINT);
But if you just define a few functions there is no need for the macros.

Answer 2

Include a .def file to defeat stdcall name decoration. Then you can get rid of the __declspec(dllexport) clutter.

Answer 3

You are not specifying any calling convention in your function declaration, so the compiiler will default to __cdecl, which decorates the exported name. Also, if you compile in C++ instead of C, additional decorating occurs as well. You need to do something like the following in your code to get around all of that:
file.h:
#ifndef fileH
#define fileH
#ifdef _BUILDING_DLL_
#define MYEXPORT __declspec (dllexport)
#else
#define MYEXPORT __declspec (dllimport)
#endif
#ifdef __cplusplus
extern "C" {
#endif
MYEXPORT void __stdcall example(int);
#ifdef __cplusplus
}
#endif
#endif
file.c:
#include <stdio.h>
#define _BUILDING_DLL_
#include "file.h"
void __stdcall example(int s1)
{
printf("dsa");
}

Answer 4

Thank you all. The solution was to add def file with exports, include it in compiler by /DEF:file.def, use Remy version (without #define _BUILDING...) and remove _stdcall.