CreateWindowEx function (User32)

Namespace: User32 Header: Winuser.h

Syntax

HWND CreateWindowExW(
    DWORD     dwExStyle,
    LPCWSTR   lpClassName,
    LPCWSTR   lpWindowName,
    DWORD     dwStyle,
    int       X,
    int       Y,
    int       nWidth,
    int       nHeight,
    HWND      hWndParent,
    HMENU     hMenu,
    HINSTANCE hInstance,
    LPVOID    lpParam
);
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The Unicode version (CreateWindowExW) is recommended; an ANSI version (CreateWindowExA) also exists.

Parameters

Name	Type	Description
dwExStyle	DWORD	Extended window style flags. See Extended Window Styles.
lpClassName	LPCWSTR	Pointer to a null‑terminated string or a class atom created by `RegisterClassEx`.
lpWindowName	LPCWSTR	Pointer to a null‑terminated string that specifies the window’s title.
dwStyle	DWORD	Window style flags. See Window Styles.
X	int	Initial horizontal position of the window.
Y	int	Initial vertical position of the window.
nWidth	int	Width of the window.
nHeight	int	Height of the window.
hWndParent	HWND	Handle to the parent or owner window.
hMenu	HMENU	Handle to a menu, or child‑window identifier.
hInstance	HINSTANCE	Handle to the instance of the module creating the window.
lpParam	LPVOID	Pointer to a value passed to the window via `WM_CREATE`.

Return Value

If the function succeeds, the return value is a handle to the new window (HWND). If it fails, the return value is NULL. To get extended error information, call GetLastError.

Remarks

The window class must be registered before calling CreateWindowEx.
Use AdjustWindowRectEx to calculate the required size of the window rectangle based on the desired client area.
After creation, the system sends a WM_CREATE message to the window procedure before the function returns.
To display the window, call ShowWindow and UpdateWindow after creation.

Examples

#include <windows.h>

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch (msg) {
        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;
    }
    return DefWindowProc(hwnd, msg, wParam, lParam);
}

int WINAPI wWinMain(HINSTANCE hInst, HINSTANCE, PWSTR, int nCmdShow)
{
    const wchar_t CLASS_NAME[] = L"SampleWindowClass";

    WNDCLASSEXW wc = {0};
    wc.cbSize        = sizeof(WNDCLASSEXW);
    wc.lpfnWndProc   = WndProc;
    wc.hInstance     = hInst;
    wc.lpszClassName = CLASS_NAME;
    wc.hCursor       = LoadCursor(nullptr, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);

    RegisterClassExW(&wc);

    HWND hwnd = CreateWindowExW(
        0,                              // Optional window styles.
        CLASS_NAME,                     // Window class
        L"CreateWindowEx Sample",       // Window text
        WS_OVERLAPPEDWINDOW,            // Window style

        // Size and position
        CW_USEDEFAULT, CW_USEDEFAULT, 500, 400,

        nullptr,       // Parent window    
        nullptr,       // Menu
        hInst,         // Instance handle
        nullptr);      // Additional application data

    if (hwnd == nullptr) return 0;

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

    MSG msg = {0};
    while (GetMessage(&msg, nullptr, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return (int)msg.wParam;
}

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