keeping DLL loop seperate from main app
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Thread: keeping DLL loop seperate from main app

  1. #1
    Join Date
    Jul 2009
    Posts
    4

    keeping DLL loop seperate from main app

    For my first program, instead of "Hello world", I made a console application that allows you to type in the name of a DLL, and the console will load it and explicitly run a function named "Initiate" from the DLL. I have a DLL that creates a Win32 window, and it goes through the usual loop to keep the window alive. It seems to work great. I can even 'cout' messages to the console from the DLL, which is kinda cool.

    So when I close the Win32 window, it frees the DLL and the console remains open, which has a goto statement to start over, and allow more input for another DLL. The problem that I am having, is that I want to be able to allow input to open another DLL right away. I'm assuming that the loop to keep the Win32 window open to proccess messages, is preventing the console from executing any further.

    However, I'm not really sure how to approach this problem. Infact, the only way I was able to get as far as I did, is with Google. But now I'm not even really sure what search term to use. I don't really know much about threads, but that would be my best guess for this situation. Is that close, or far off?

    Here is my code...

    RunDLL: (console app to load DLL)
    Code:
    #include <iostream>
    #include <string>
    #include <windows.h>
    
    std::string str_input;
    typedef int (*INIT)(HWND, HINSTANCE, int);
    
    int main()
    {
    	char t[500]; // Create var to hold title
    	GetConsoleTitleA(t, 500); // Get title and assign to var
    	HWND hwndConsole = FindWindowA( NULL, t ); // Assign HWND by search for title
    	HINSTANCE hInstance = (HINSTANCE)GetWindowLong(hwndConsole, GWL_HINSTANCE); // Get handle instance using HWND
    
    	load: // LOAD SEQUENCE
    	std::cout << "> ";
    	std::cin >> str_input;
    
    	if (str_input == TEXT("exit")) goto exit;
    
    	HINSTANCE hInstLibrary = LoadLibrary(str_input.c_str());
    
    	if (hInstLibrary)
    	{
    		INIT Initiate = (INIT)GetProcAddress(hInstLibrary, "Initiate");
    
    		if (Initiate)
    		{
    			Initiate(hwndConsole, hInstance, SW_SHOWNORMAL);
    		}
    
    		FreeLibrary(hInstLibrary);
    	}
    	else
    	{
    		std::cout << "DLL failed to load" << std::endl;
    	}
    
    	goto load;
    
    	exit: // EXIT SEQUENCE
    	return 0;
    }
    DLL:
    Code:
    #include "windows.h"
    #include <iostream>
    #include <string>
    
    extern "C"
    {
    	__declspec(dllexport) int Initiate(HWND, HINSTANCE, int);
    }
    
    LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam);
    void console_msg(std::string coutMsg);
    
    extern "C"
    {
    //	DECLDIR int Initiate(HWND conhwnd, HINSTANCE hInstance, LPSTR lpszCmdLine, int nCmdShow)
    	__declspec(dllexport) int Initiate(HWND conhwnd, HINSTANCE hInstance, int nCmdShow)
    	{
    		console_msg("Initiate called");
    
    		WNDCLASS wc;
    		wc.cbClsExtra = 0;
    		wc.cbWndExtra = 0;
    		wc.hbrBackground = (HBRUSH)GetStockObject( WHITE_BRUSH );
    		wc.hCursor = LoadCursor( NULL, IDC_ARROW );
    		wc.hIcon = LoadIcon( NULL, IDI_APPLICATION );
    		wc.hInstance = hInstance;
    		wc.lpfnWndProc = WndProc;
    		wc.lpszClassName = TEXT("WinClass");
    		wc.lpszMenuName = 0;
    		wc.style = CS_HREDRAW | CS_VREDRAW;
    		RegisterClass(&wc);
    
    		HWND hwnd = CreateWindow(TEXT("WinClass"), TEXT("windows title"), WS_OVERLAPPEDWINDOW, 10, 10, 200, 200, NULL, NULL, hInstance, NULL );
    
    		ShowWindow(hwnd, nCmdShow);
    		UpdateWindow(hwnd);
    
    		MSG msg;
    
    		while(GetMessage(&msg, NULL, 0, 0))
    		{
    			TranslateMessage(&msg);
    			DispatchMessage(&msg);
    		}
    
    		return msg.wParam;
    	}
    }
    
    LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam)
    {
    	switch( message )
    	{
    		case WM_CREATE:
    			console_msg("Window created");
    		break;
    		case WM_PAINT:
    		break;
    		case WM_DESTROY:
    			console_msg("Unloading library...");
    			PostQuitMessage( 0 ) ;
    			return 0;
    		break;
    	}
    
    	return DefWindowProc( hwnd, message, wparam, lparam );
    }
    
    void console_msg(std::string coutMsg)
    {
    	std::cout << "DLL.dll> " << coutMsg << std::endl;
    }
    If anyone decides to compile this, compile it with character set "not set". That was a real pain to figure out. This conversation is open for any kind of suggestions or feedback, so please comment.

    For RunDLL, I see a future problem I'm going to need to figure out.
    Code:
    		INIT Initiate = (INIT)GetProcAddress(hInstLibrary, "Initiate");
    
    		if (Initiate)
    		{
    			Initiate(hwndConsole, hInstance, SW_SHOWNORMAL);
    		}
    
    		FreeLibrary(hInstLibrary);
    It frees the library as soon as 'Initiate' is finished. I realize this, and I'm sure it's not a big deal as of right now...

  2. #2
    Join Date
    Feb 2009
    Location
    India
    Posts
    444

    Re: keeping DLL loop seperate from main app

    Create a new thread each time the name of a DLL is entered using CreateThread.
    The LoadLibrary and the if / else code must be put into the thread function.
    _Superman_
    I love work. It gives me something to do between weekends.

    Microsoft MVP (Visual C++)

  3. #3
    Join Date
    Jul 2009
    Posts
    4

    Re: keeping DLL loop seperate from main app

    Thank you very much. It's weird how searching Google for "C++ CreateThread" happens to come up with some better examples, then searching for something like "C++ threads".

  4. #4
    Join Date
    Jul 2009
    Posts
    4

    Re: keeping DLL loop seperate from main app

    I found this great example on MSDN, through this site.
    http://msdn.microsoft.com/en-us/libr...16(VS.85).aspx

    Just for anyone who might have troubles finding it, one more link might make it easier.

  5. #5
    Join Date
    Jul 2009
    Posts
    4

    Re: keeping DLL loop seperate from main app

    I have a question; when a thread function returns, does the thread terminate?

  6. #6
    Join Date
    Feb 2009
    Location
    India
    Posts
    444

    Re: keeping DLL loop seperate from main app

    That is correct.
    _Superman_
    I love work. It gives me something to do between weekends.

    Microsoft MVP (Visual C++)

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