Win32 DLL which have a Window

Question

I'd like to make a Win32 DLL.

This DLL will have only one function of which name is DS_Entry().

Dll's DS_Entry() function should create a window which have only [Close] button.

If I create Win32 DLL project, DllMain() exists.

In case of Win32 Application, there's WinMain and WndProc.

I have no idea where do I add this code in DLL.

Can anybody give some idea?

Answer 1

For a quick start, just call MessageBox from your function. The button will be labeled OK, with some other options.

By the way a DLL can have only one function only if its name is DllMain. Otherwise, it wold have two or more functions ;)

Answer 2

WinMain is the entry point for a windows application (.exe). The entry point for a DLL is DLLMain.

WndProc is a function known as a window procedure.  Every window has a window procedure that handles window messages that are dispatched to the related window or passes them to the default window procedure for processing. The RegisterClass/RegisterClassEx functions associate a WndProc with the window created by CreateWindow/CreateWindowEx.

If you use the Visual Studio new project wizard to create a Win32 application project and a Win32 DLL project you will be able to see these items in the source code that is generated by the wizard.

You can include all the code necessary within a DLL to create a window. You will have to properly export a function from the DLL so that it is accessible to an application that uses it.  If you use the Win32 DLL project wizard to create a DLL project make sure to specify that it should create exports.  The generated code will then include examples of exported functions. 

Answer 3

The following is some eample code that creates a DLL. The DLL exports a function that can be used to create a window.  I hope you find it informative.

MyDLL.h :

// The following ifdef block is the standard way of creating macros which make exporting 
// from a DLL simpler. All files within this DLL are compiled with the MYDLL_EXPORTS
// symbol defined on the command line. This symbol should not be defined on any project
// that uses this DLL. This way any other project whose source files include this file see 
// MYDLL_API functions as being imported from a DLL, whereas this DLL sees symbols
// defined with this macro as being exported.
#ifdef MYDLL_EXPORTS
#define MYDLL_API __declspec(dllexport)
#else
#define MYDLL_API __declspec(dllimport)
#endif

// Functions exported from the MyDLL.dll
MYDLL_API int CALLBACK  plus(int x, int y);
MYDLL_API HWND CALLBACK ShowDLLWindow(HWND hParent, LPCWSTR lpszWindowCaption);

MyDLL.cpp

// MyDLL.cpp : Defines the exported functions for the DLL application.
//

#include "stdafx.h"
#include "resource.h"
#include "MyDLL.h"

HMODULE hDLLInstance; // set in DLLMain

LRESULT CALLBACK	DLLWndProc(HWND, UINT, WPARAM, LPARAM);

// DLLMain defines the entry point for the DLL.
BOOL APIENTRY DllMain(HMODULE hModule,
	DWORD  ul_reason_for_call,
	LPVOID lpReserved
	)
{
	switch (ul_reason_for_call)
	{
	case DLL_PROCESS_ATTACH:
	case DLL_THREAD_ATTACH:
	case DLL_THREAD_DETACH:
	case DLL_PROCESS_DETACH:
		hDLLInstance = hModule;
		break;
	}
	return TRUE;
}


//  Register the window class used in the ShowDLLWindow function to create a window.
ATOM RegisterDLLWndClass(HINSTANCE hInstance)
{
	WNDCLASSEX wcex;

	wcex.cbSize = sizeof(WNDCLASSEX);

	wcex.style = CS_HREDRAW | CS_VREDRAW;
	wcex.lpfnWndProc = DLLWndProc;
	wcex.cbClsExtra = 0;
	wcex.cbWndExtra = 0;
	wcex.hInstance = hInstance;
	wcex.hIcon = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_ICON1));
	wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
	wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
	wcex.lpszMenuName = NULL;
	wcex.lpszClassName = L"MyDLLWindow";
	wcex.hIconSm = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_ICON2));

	return RegisterClassEx(&wcex);
}


//This is the WndProc for the window created by the exported DLL ShowDLLWindow function
LRESULT CALLBACK DLLWndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	PAINTSTRUCT ps;
	HDC hdc;

	switch (message)
	{
	case WM_PAINT:
		hdc = BeginPaint(hWnd, &ps);
		// TODO: Add any drawing code here...
		EndPaint(hWnd, &ps);
		break;

	default:
		return DefWindowProc(hWnd, message, wParam, lParam);
	}
	return 0;
}


//This function is exported and creates a window
MYDLL_API HWND CALLBACK ShowDLLWindow(HWND hParent, LPCWSTR lpszWindowCaption)
{
	RegisterDLLWndClass(hDLLInstance);

	HWND hWnd = CreateWindow(L"MyDLLWindow", lpszWindowCaption, WS_OVERLAPPEDWINDOW,
		CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, hParent, NULL, hDLLInstance, NULL);

	if (hWnd != NULL)
	{
		ShowWindow(hWnd, SW_SHOW);
		UpdateWindow(hWnd);
	}

	return hWnd;
}

// This is an example of an exported function.
MYDLL_API  int CALLBACK plus(int x, int y)
{
	return (x + y);
}