Programming Forums > Application Development > C++

Writlaus · Mar 9th, 2006, 4:51 PM

I'm just getting started with the Win32 API, and I can't seem to display some simple text when the user clicks the middle button of the mouse. It doesn't show any error message--it just closes, as if I had closed it. Could anyone help? I'm sure it's something simple...

(Toggle Plain Text)

#include <windows.h>

const char g_szClassName[] = "myWindowClass";

// Step 4: the Window Procedure
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch(msg)
    {
        case WM_LBUTTONDOWN:
        {
            char szFileName[MAX_PATH];
            HINSTANCE hInstance = GetModuleHandle(NULL);

            GetModuleFileName(hInstance, szFileName, MAX_PATH);
            MessageBox(hwnd, szFileName, "This program is:", MB_OK | MB_ICONINFORMATION);
        }
        break;
        case WM_MBUTTONDOWN:
        {
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hwnd, &ps);

            TextOut(hdc,10,10,"Hello World",11);

            EndPaint(hwnd, &ps);
        }
        case WM_CLOSE:
            DestroyWindow(hwnd);
        break;
        case WM_DESTROY:
            PostQuitMessage(0);
        break;
        default:
            return DefWindowProc(hwnd, msg, wParam, lParam);
    }
    return 0;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
    LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASSEX wc;
    HWND hwnd;
    MSG Msg;

    //Step 1: Registering the Window Class
    wc.cbSize        = sizeof(WNDCLASSEX);
    wc.style         = 0;
    wc.lpfnWndProc   = WndProc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.hInstance     = hInstance;
    wc.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor       = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
    wc.lpszMenuName  = NULL;
    wc.lpszClassName = g_szClassName;
    wc.hIconSm       = LoadIcon(NULL, IDI_APPLICATION);

    if(!RegisterClassEx(&wc))
    {
        MessageBox(NULL, "Window Registration Failed!", "Error!",
            MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

    // Step 2: Creating the Window
    hwnd = CreateWindowEx(
        0,
        g_szClassName,
        "The title of my window",
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 240, 120,
        NULL, NULL, hInstance, NULL);

    if(hwnd == NULL)
    {
        MessageBox(NULL, "Window Creation Failed!", "Error!",
            MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

    // Step 3: The Message Loop
    while(GetMessage(&Msg, NULL, 0, 0) > 0)
    {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }
    return Msg.wParam;
}

#include <windows.h>

const char g_szClassName[] = "myWindowClass";

// Step 4: the Window Procedure
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch(msg)
    {
        case WM_LBUTTONDOWN:
        {
            char szFileName[MAX_PATH];
            HINSTANCE hInstance = GetModuleHandle(NULL);

            GetModuleFileName(hInstance, szFileName, MAX_PATH);
            MessageBox(hwnd, szFileName, "This program is:", MB_OK | MB_ICONINFORMATION);
        }
        break;
        case WM_MBUTTONDOWN:
        {
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hwnd, &ps);

            TextOut(hdc,10,10,"Hello World",11);

            EndPaint(hwnd, &ps);
        }
        case WM_CLOSE:
            DestroyWindow(hwnd);
        break;
        case WM_DESTROY:
            PostQuitMessage(0);
        break;
        default:
            return DefWindowProc(hwnd, msg, wParam, lParam);
    }
    return 0;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
    LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASSEX wc;
    HWND hwnd;
    MSG Msg;

    //Step 1: Registering the Window Class
    wc.cbSize        = sizeof(WNDCLASSEX);
    wc.style         = 0;
    wc.lpfnWndProc   = WndProc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.hInstance     = hInstance;
    wc.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor       = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
    wc.lpszMenuName  = NULL;
    wc.lpszClassName = g_szClassName;
    wc.hIconSm       = LoadIcon(NULL, IDI_APPLICATION);

    if(!RegisterClassEx(&wc))
    {
        MessageBox(NULL, "Window Registration Failed!", "Error!",
            MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

    // Step 2: Creating the Window
    hwnd = CreateWindowEx(
        0,
        g_szClassName,
        "The title of my window",
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 240, 120,
        NULL, NULL, hInstance, NULL);

    if(hwnd == NULL)
    {
        MessageBox(NULL, "Window Creation Failed!", "Error!",
            MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

    // Step 3: The Message Loop
    while(GetMessage(&Msg, NULL, 0, 0) > 0)
    {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }
    return Msg.wParam;
}

Cache · Mar 9th, 2006, 5:23 PM

The case statement for 'WM_MBUTTONDOWN' doesn't 'break', so it's falling through into the 'WM_CLOSE' case which closes the window.

Cache · Mar 9th, 2006, 6:45 PM

Also, MSDN specifies that:

Quote:

An application should not call BeginPaint except in response to a WM_PAINT message.

Writlaus · Mar 10th, 2006, 1:23 AM

Why thank you, that obviously helped a lot. I knew it was something simple

Writlaus · Mar 10th, 2006, 2:12 AM

Quote:

An application should not call BeginPaint except in response to a WM_PAINT message.

Does that mean it won't work if I call it when not responding to a WM_PAINT message? Because now my code won't close, but it also won't display the text.

Mjordan2nd · Mar 10th, 2006, 2:56 AM

If you want to do it outside WM_PAINT and not use BeginPaint(), you could use:

(Toggle Plain Text)

hdc=GetDC(hwnd);

When the device context is no longer needed, make sure you call:

(Toggle Plain Text)

ReleaseDC(hwnd, hdc);

grumpy · Mar 10th, 2006, 3:01 AM

Quote:

Originally Posted by Writlaus

Does that mean it won't work if I call it when not responding to a WM_PAINT message? Because now my code won't close, but it also won't display the text.

As I understand it, when a program receives a WM_PAINT message, there will be some defined region that has to be (re)painted. When a program receives other messages, such a region is not necessarily defined (it will normally be the whole screen or window, rather than a region to be repainted, but can also be related to some other settings that are unrelated to what the programmer is trying to do) so the effect of BeginPaint() or the code after it becomes unpredictable.

In particular, because BeginPaint() sets a clipping region (and invalidates background in some circumstances), it is possible that the code after it will not have intended effects (eg if it does things outside the clipping region).

As a general rule, when documentation for a library says "only do it this way", the reason is that the designers of that library found it impossible to ensure the function worked correctly if you ignore their statement. Library writers don't tend to like to admit defeat by adding such clauses and, when they do, there is usually a good reason.

Writlaus · Mar 10th, 2006, 4:11 PM

Ah, all is clear (for now, heh). The text displayed alright. Thank you, very much.

Mar 9th, 2006, 4:51 PM	#1
Writlaus Hobbyist Programmer Join Date: Nov 2005 Posts: 149 Rep Power: 3	win32 api I'm just getting started with the Win32 API, and I can't seem to display some simple text when the user clicks the middle button of the mouse. It doesn't show any error message--it just closes, as if I had closed it. Could anyone help? I'm sure it's something simple... (Toggle Plain Text) #include <windows.h> const char g_szClassName[] = "myWindowClass"; // Step 4: the Window Procedure LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) { switch(msg) { case WM_LBUTTONDOWN: { char szFileName[MAX_PATH]; HINSTANCE hInstance = GetModuleHandle(NULL); GetModuleFileName(hInstance, szFileName, MAX_PATH); MessageBox(hwnd, szFileName, "This program is:", MB_OK \| MB_ICONINFORMATION); } break; case WM_MBUTTONDOWN: { PAINTSTRUCT ps; HDC hdc = BeginPaint(hwnd, &ps); TextOut(hdc,10,10,"Hello World",11); EndPaint(hwnd, &ps); } case WM_CLOSE: DestroyWindow(hwnd); break; case WM_DESTROY: PostQuitMessage(0); break; default: return DefWindowProc(hwnd, msg, wParam, lParam); } return 0; } int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) { WNDCLASSEX wc; HWND hwnd; MSG Msg; //Step 1: Registering the Window Class wc.cbSize = sizeof(WNDCLASSEX); wc.style = 0; wc.lpfnWndProc = WndProc; wc.cbClsExtra = 0; wc.cbWndExtra = 0; wc.hInstance = hInstance; wc.hIcon = LoadIcon(NULL, IDI_APPLICATION); wc.hCursor = LoadCursor(NULL, IDC_ARROW); wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1); wc.lpszMenuName = NULL; wc.lpszClassName = g_szClassName; wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION); if(!RegisterClassEx(&wc)) { MessageBox(NULL, "Window Registration Failed!", "Error!", MB_ICONEXCLAMATION \| MB_OK); return 0; } // Step 2: Creating the Window hwnd = CreateWindowEx( 0, g_szClassName, "The title of my window", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, 240, 120, NULL, NULL, hInstance, NULL); if(hwnd == NULL) { MessageBox(NULL, "Window Creation Failed!", "Error!", MB_ICONEXCLAMATION \| MB_OK); return 0; } ShowWindow(hwnd, nCmdShow); UpdateWindow(hwnd); // Step 3: The Message Loop while(GetMessage(&Msg, NULL, 0, 0) > 0) { TranslateMessage(&Msg); DispatchMessage(&Msg); } return Msg.wParam; } #include <windows.h> const char g_szClassName[] = "myWindowClass"; // Step 4: the Window Procedure LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) { switch(msg) { case WM_LBUTTONDOWN: { char szFileName[MAX_PATH]; HINSTANCE hInstance = GetModuleHandle(NULL); GetModuleFileName(hInstance, szFileName, MAX_PATH); MessageBox(hwnd, szFileName, "This program is:", MB_OK \| MB_ICONINFORMATION); } break; case WM_MBUTTONDOWN: { PAINTSTRUCT ps; HDC hdc = BeginPaint(hwnd, &ps); TextOut(hdc,10,10,"Hello World",11); EndPaint(hwnd, &ps); } case WM_CLOSE: DestroyWindow(hwnd); break; case WM_DESTROY: PostQuitMessage(0); break; default: return DefWindowProc(hwnd, msg, wParam, lParam); } return 0; } int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) { WNDCLASSEX wc; HWND hwnd; MSG Msg; //Step 1: Registering the Window Class wc.cbSize = sizeof(WNDCLASSEX); wc.style = 0; wc.lpfnWndProc = WndProc; wc.cbClsExtra = 0; wc.cbWndExtra = 0; wc.hInstance = hInstance; wc.hIcon = LoadIcon(NULL, IDI_APPLICATION); wc.hCursor = LoadCursor(NULL, IDC_ARROW); wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1); wc.lpszMenuName = NULL; wc.lpszClassName = g_szClassName; wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION); if(!RegisterClassEx(&wc)) { MessageBox(NULL, "Window Registration Failed!", "Error!", MB_ICONEXCLAMATION \| MB_OK); return 0; } // Step 2: Creating the Window hwnd = CreateWindowEx( 0, g_szClassName, "The title of my window", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, 240, 120, NULL, NULL, hInstance, NULL); if(hwnd == NULL) { MessageBox(NULL, "Window Creation Failed!", "Error!", MB_ICONEXCLAMATION \| MB_OK); return 0; } ShowWindow(hwnd, nCmdShow); UpdateWindow(hwnd); // Step 3: The Message Loop while(GetMessage(&Msg, NULL, 0, 0) > 0) { TranslateMessage(&Msg); DispatchMessage(&Msg); } return Msg.wParam; }

Mar 10th, 2006, 2:56 AM	#6
Mjordan2nd The Supreme Ruler Join Date: May 2004 Location: Houston Posts: 1,476 Rep Power: 6	If you want to do it outside WM_PAINT and not use BeginPaint(), you could use: (Toggle Plain Text) hdc=GetDC(hwnd); hdc=GetDC(hwnd); When the device context is no longer needed, make sure you call: (Toggle Plain Text) ReleaseDC(hwnd, hdc); ReleaseDC(hwnd, hdc); __________________ "Every gun that is made, every warship launched, every rocket signifies, in the final sense, a theft from those who hunger and are not fed, from those who are cold and are not clothed. The world in arms is not spending money alone. It is spending the sweat of its laborers, the genius of its scientists, the hopes of its children." - Dwight D. Eisenhower

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Mar 9th, 2006, 5:23 PM	#2
Cache Hobbyist Join Date: Sep 2005 Posts: 261 Rep Power: 4	The case statement for 'WM_MBUTTONDOWN' doesn't 'break', so it's falling through into the 'WM_CLOSE' case which closes the window.

Mar 10th, 2006, 1:23 AM	#4
Writlaus Hobbyist Programmer Join Date: Nov 2005 Posts: 149 Rep Power: 3	Why thank you, that obviously helped a lot. I knew it was something simple

Mar 10th, 2006, 4:11 PM	#8
Writlaus Hobbyist Programmer Join Date: Nov 2005 Posts: 149 Rep Power: 3	Ah, all is clear (for now, heh). The text displayed alright. Thank you, very much.

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Programming Forums > Application Development > C++

win32 api