D for Win32

Introduction

This describes the D implementation for 32 bit Windows systems. Naturally, Windows specific D features are not portable to other platforms.

Instead of the:

#include <windows.h>

of C, in D there is:

import core.sys.windows.windows;

Calling Conventions

In C, the Windows API calling conventions are __stdcall. In D, it is simply:

extern (Windows)
{
    /* ... function declarations ... */
}

The Windows linkage attribute sets both the calling convention and the name mangling scheme to be compatible with Windows.

For functions that in C would be __declspec(dllimport) or __declspec(dllexport), use the export attribute:

export void func(int foo);

If no function body is given, it's imported. If a function body is given, it's exported.

Windows Executables

Windows GUI applications can be written with D. A sample such can be found in \samples\d\winsamp.d

On Win32, you can pass -L/subsystem:windows if you don't want a console to be automatically allocated.

Please note when compiling on Win64, you need to explicitly list -Lgdi32.lib -Luser32.lib on the build command. If you want the Windows subsystem too, use -L/subsystem:windows -L/entry:mainCRTStartup.

If using ldc instead of dmd, use -L/entry:wmainCRTStartup instead of mainCRTStartup; note the "w".

It is possible to do this with a mixin too in a library, see arsd.simpledisplay mixin EnableWindowsSubsystem for an example.

With the Windows subsystem, there is no console, so standard writeln will throw!

Alternative option:

1. Instead of a main function serving as the entry point, a WinMain function is needed.

2. WinMain must follow this form:

import core.runtime;
import core.sys.windows.windows;
import std.string;

extern (Windows)
int WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
            LPSTR lpCmdLine, int nCmdShow)
{
    int result;

    try
    {
        Runtime.initialize();
        result = myWinMain(hInstance, hPrevInstance, lpCmdLine, nCmdShow);
        Runtime.terminate();
    }
    catch (Throwable e) 
    {
        MessageBoxA(null, e.toString().toStringz(), null,
                    MB_ICONEXCLAMATION);
        result = 0;     // failed
    }

    return result;
}

int myWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
              LPSTR lpCmdLine, int nCmdShow)
{
    // ... insert user code here ...
    return 0;
}

The myWinMain() function is where the user code goes, the rest of WinMain is boilerplate to initialize and shut down the D runtime system.

3. A .def (Module Definition File) with at least the following two lines in it:

EXETYPE NT
SUBSYSTEM WINDOWS

Without those, Win32 will open a text console window whenever the application is run.

4. The presence of WinMain() is recognized by the compiler causing it to emit a reference to __acrtused_dll and the phobos.lib runtime library.

Windows Programming Examples

A collection of over 140 Windows D programming code examples is available at this Github repository.