C++ CreateWindowEx返回NULL

Question

我试图使用C++设置一个简单的窗口，但我对CreateWindowEx的调用返回NULL。我使用的大部分代码都来自MSDN网站上的example。我尝试过的方法都不起作用，任何帮助都将不胜感激。

代码如下：

//Include the windows header
#include <Windows.h>

//Forward declaration of the WndProc function
LRESULT CALLBACK WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);

//Main entry point
int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PWSTR pCmdLine, int nCmdShow) {
    //Window class name
    const wchar_t windowName[] = L"Window Class";

    //Set up window class
    WNDCLASS wnd;
    wnd.lpfnWndProc = WndProc;
    wnd.hInstance = hInstance;
    wnd.lpszClassName = windowName;

    //Register window class
    RegisterClass(&wnd);

    //Create window
    //! This returns NULL
    HWND hWnd = CreateWindowEx(
        0,
        windowName,
        L"Windows Programming",
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        NULL,
        NULL,
        hInstance,
        NULL
        );

    //Simple check to see if window creation failed
    if(hWnd == NULL) {
            //Pause
        system("PAUSE");
        return -1;
    }

    //Show the window
    ShowWindow(hWnd, nCmdShow);

    //Main message loop
    MSG msg;
    while(GetMessage(&msg, NULL, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
}

//WndProc function
LRESULT CALLBACK WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam) {
    switch(msg) {
    case WM_PAINT:
        {
            PAINTSTRUCT ps;
            HDC hDc = BeginPaint(hWnd, &ps);

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

            EndPaint(hWnd, &ps);

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

    return DefWindowProc(hWnd, msg, wParam, lParam);
}

Answer 1

请注意，来自MSDN的示例在设置它所关心的字段之前将WNDCLASS的所有字段置零。

WNDCLASS wnd = { };  // from MSDN example

空大括号是C和C++的缩写，用于将整个结构初始化为0。将其编写为{ 0 }也很常见，它在技术上略有不同，但具有相同的净效果。

在您的代码中，您删除了初始化：

WNDCLASS wnd;  // your code

因此，您可能会在其他重要字段中获得一些垃圾值，比如cbClsExtra或cbWndExtra，这会导致类无法注册。因为类没有注册，所以不能创建该类的窗口。

Answer 2

我已经让你的代码正常工作了。基本上，我在使用WNDCLASS (或WNDCLASSEX)结构时所做的就是使用所有参数，以确保不会遗漏某些东西。

//Include the windows header
#include <Windows.h>

//Forward declaration of the WndProc function
LRESULT CALLBACK WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);

//Main entry point
int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PWSTR pCmdLine, int nCmdShow) {
    //Window class name
    const wchar_t windowName[] = L"Window Class";

    //Set up window class
    WNDCLASS wnd;
    wnd.cbClsExtra = 0;
    wnd.cbWndExtra = 0;
    wnd.hCursor = LoadCursor(0, IDC_ARROW);
    wnd.hIcon = LoadIcon(0, IDI_WINLOGO);
    wnd.lpszMenuName = 0;
    wnd.style = 0;
    wnd.hbrBackground = 0;
    wnd.lpfnWndProc = WndProc;
    wnd.hInstance = hInstance;
    wnd.lpszClassName = windowName;

    //Register window class
    RegisterClass(&wnd);

    //Create window
    //! This returns NULL
    HWND hWnd = CreateWindowEx(
        0,
        windowName,
        L"Windows Programming",
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        NULL,
        NULL,
        hInstance,
        NULL
        );

    //Simple check to see if window creation failed
    if(hWnd == NULL) {
            //Pause
        system("PAUSE");
        return -1;
    }

    //Show the window
    ShowWindow(hWnd, nCmdShow);

    //Main message loop
    MSG msg;
    while(GetMessage(&msg, NULL, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
}

//WndProc function
LRESULT CALLBACK WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam) {
    switch(msg) {
    case WM_PAINT:
        {
            PAINTSTRUCT ps;
            HDC hDc = BeginPaint(hWnd, &ps);

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

            EndPaint(hWnd, &ps);

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

    return DefWindowProc(hWnd, msg, wParam, lParam);
}