D for Win32

Windows

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

These are required:

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

    void exceptionHandler(Throwable e) {
        throw e;
    }

    try
    {
        Runtime.initialize(&exceptionHandler);
        result = myWinMain(hInstance, hPrevInstance, lpCmdLine, nCmdShow);
        Runtime.terminate(&exceptionHandler);
    }
    catch (Throwable e) // catch any uncaught exceptions
    {
        MessageBoxA(null, e.toString().toStringz(), "Error",
                    MB_OK | 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. 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. The presence of WinMain() is recognized by the compiler causing it to emit a reference to __acrtused_dll and the phobos.lib runtime library.