Windows 键盘消息和 Alt 键

Question

我试图了解消息循环和一般键盘消息在Windows系统中是如何工作的。 我编写了一个带有消息循环的简单程序：

// include the basic windows header file
#include <windows.h>
#include <windowsx.h>
#include <stdio.h>

// the WindowProc function prototype
LRESULT CALLBACK WindowProc(HWND hWnd,
    UINT message,
    WPARAM wParam,
    LPARAM lParam);

char MsgBuff[300];

template <typename T>
char* BinVal(T SrcVal) {

    const short BitsCount = sizeof(T) * CHAR_BIT;
    const short SeparatorCount = sizeof(T) * 2 - 1;
    static char BinValStr[BitsCount + SeparatorCount] = { 0 };

    printf("BitsCount: %d\n", BitsCount);
    printf("SeparatorCount: %d\n", SeparatorCount);
    printf("BinValStr size: %d\n", BitsCount + SeparatorCount);

    int i = 0;
    int j = 0;

    for (i = BitsCount + SeparatorCount - 1; i >= 0; i--) {

        if ((j + 1) % 5 == 0) {
            BinValStr[i] = ' ';
        }
        else {
            if ((SrcVal & 1) == 1)
                BinValStr[i] = '1';
            else
                BinValStr[i] = '0';
            SrcVal >>= 1;
        }
        j++;
        //printf(": %d, %d\n", i, SrcVal&1);

    }
    return BinValStr;
}

// the entry point for any Windows program
int WINAPI WinMain(
    _In_ HINSTANCE hInstance,
    _In_opt_ HINSTANCE hPrevInstance,
    _In_ LPSTR lpCmdLine,
    _In_ int nCmdShow) {
    // the handle for the window, filled by a function
    HWND hWnd;
    // this struct holds information for the window class
    WNDCLASSEX wc;



    // clear out the window class for use
    ZeroMemory(&wc, sizeof(WNDCLASSEX));

    // fill in the struct with the needed information
    wc.cbSize = sizeof(WNDCLASSEX);
    wc.style = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc = WindowProc;
    wc.hInstance = hInstance;
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)COLOR_WINDOW;
    wc.lpszClassName = L"WindowClass1";

    // register the window class
    RegisterClassEx(&wc);

    // create the window and use the result as the handle
    hWnd = CreateWindowEx(NULL,
        L"WindowClass1",    // name of the window class
        L"Our First Windowed Program",    // title of the window
        WS_OVERLAPPEDWINDOW,    // window style
        300,    // x-position of the window
        300,    // y-position of the window
        500,    // width of the window
        400,    // height of the window
        NULL,    // we have no parent window, NULL
        NULL,    // we aren't using menus, NULL
        hInstance,    // application handle
        NULL);    // used with multiple windows, NULL

// display the window on the screen
    ShowWindow(hWnd, nCmdShow);

    // enter the main loop:

    // this struct holds Windows event messages
    MSG msg;

    // Enter the infinite message loop
    while (TRUE) {
        // Check to see if any messages are waiting in the queue
        while (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
        {
            // translate keystroke messages into the right format
            TranslateMessage(&msg);

            // send the message to the WindowProc function
            DispatchMessage(&msg);
        }

        // If the message is WM_QUIT, exit the while loop
        if (msg.message == WM_QUIT)
            break;

    }

    // return this part of the WM_QUIT message to Windows
    return msg.wParam;
}

int LoopCnt = 0;
int BinMask = 0b00000000'00000000'00000000'11111111;

// this is the main message handler for the program
LRESULT CALLBACK WindowProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam) {
    switch (message) {

        case WM_DESTROY: {
            PostQuitMessage(0);
        } break;

        case WM_KEYDOWN: {
            sprintf_s(MsgBuff, 300, "WM_KEYDOWN(#%i) wParam (virtual-key code): %d (%Xh), scan code: %X, lParam(bin): %s\n", LoopCnt, wParam, wParam, lParam & BinMask, BinVal(lParam));
            OutputDebugStringA(MsgBuff);
        } break;

        case WM_CHAR: {
            sprintf_s(MsgBuff, 300, "WM_CHAR(#%i) wParam (virtual-key code): %d (%Xh), scan code: %X, lParam(bin): %s\n", LoopCnt, wParam, wParam, lParam & BinMask, BinVal(lParam));
            OutputDebugStringA(MsgBuff);
        } break;

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

    }

    LoopCnt++;
}

在那里我检查了扫描代码发送的WM_KEYDOWN消息lParam参数。

现在我有以下问题：

1. 为什么left Alt键不会生成WM_KEYDOWN消息，而right Alt会生成？ （调试器不会 go 进入WM_KEYDOWN:按下左 Alt 时的case 语句）
2. 为什么按下right Alt键会同时生成两条WM_KEYDOWN消息 - 分别具有 1D（十六进制）和 38（十六进制）扫描码？