WM_CHAR - incorrect wParam

Question

I have successfully built and run an example Win Api application. Next I have added handling for WM_CHAR and WM_SYSCHAR messages:

#include <windows.h>

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PWSTR pCmdLine, int nCmdShow)
{
    // Register the window class.
    const wchar_t CLASS_NAME[]  = L"Sample Window Class";

    WNDCLASS wc = { };

    wc.lpfnWndProc   = WindowProc;
    wc.hInstance     = hInstance;
    wc.lpszClassName = CLASS_NAME;

    RegisterClass(&wc);

    // Create the window.

    HWND hwnd = CreateWindowEx(
        0,                              // Optional window styles.
        CLASS_NAME,                     // Window class
        L"Learn to Program Windows",    // Window text
        WS_OVERLAPPEDWINDOW,            // Window style

        // Size and position
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,

        NULL,       // Parent window    
        NULL,       // Menu
        hInstance,  // Instance handle
        NULL        // Additional application data
    );

    if (hwnd == NULL)
    {
        return 0;
    }

    ShowWindow(hwnd, nCmdShow);

    // Run the message loop.

    MSG msg = { };
    while (GetMessage(&msg, NULL, 0, 0) > 0)
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return 0;
}

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch (uMsg)
    {
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;

    case WM_PAINT:
        {
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hwnd, &ps);

            // All painting occurs here, between BeginPaint and EndPaint.

            FillRect(hdc, &ps.rcPaint, (HBRUSH) (COLOR_WINDOW+1));

            EndPaint(hwnd, &ps);
        }
        return 0;
    case WM_CHAR:
    case WM_SYSCHAR:
        {
            UINT32 codepoint = (UINT32)wParam;
        }
        return 0;
    }
    return DefWindowProc(hwnd, uMsg, wParam, lParam);
}

The only purpose of the above code is to see during debugging a codepoint for the pressed key. According to my language settings I should get the codepoint 261 after pressing AltGr + a but I get the codepoint 185. I have also built and run an example application which uses GLFW library and set a char callback using glfwSetCharCallback fucntion. That callback is called with codepoint 261 after pressing AltGr + a. It looks like that my Win Api code has some lacks but after looking at GLFW source code I have no idea why I get a different codepoint in my application. It is not related to handling WM_KEYDOWN,WM_SYSKEYDOWN,WM_KEUP and WM_SYSKEYUP messages - I have commented out that code in GLFW and the char callback works fine. Where is the problem ?

Answer 1

Using the Unicode version of the RegisterClass function(RegisterClassW) works.

The WM_CHAR message uses UTF-16 (16-bit Unicode Transformation Format) code units in its wParam if the Unicode version of the RegisterClass function was used to register the window class.

UTF-16 will complement code point correctly.