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Limina102's questions

Martin Hope
Limina102
Asked: 2024-11-17 14:43:40 +0800 CST
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我写了一段代码来学习SetTimer和KillTimer，首先在WM_CREATE中设置一个定时器，然后在定时器的回调函数中写上KillTimer，这样定时器只会被调用一次。

我在定时器回调函数中放置了一个 MessageBox，这样当定时器被调用时，MessageBox 会弹出来提示。MessageBox 预计只会弹出一次，因为定时器会在 MessageBox 调用后立即被 KillTimer 关闭。

但是，程序并没有按照预期运行。看来 KillTimer 并没有按照指示停止计时器。相反，程序不断弹出消息框。

以下是代码：

#include <stdio.h>
#include <windows.h>

VOID CALLBACK timer_proc(HWND hwnd, UINT msg, UINT timer_id, DWORD time)
{
        char buf[1024];
        sprintf(buf, "TIMER PROC CALLED AT %d, ID %d", time, timer_id);
        MessageBoxA(hwnd, buf, "MSGBOX", MB_ICONINFORMATION);
        KillTimer(hwnd, timer_id);
}

void wm_paint(HWND hwnd)
{
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hwnd, &ps);
        TextOutA(hdc, 20, 20, "Hi?", 3);
        EndPaint(hwnd, &ps);
}

LRESULT CALLBACK wndproc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp)
{
        switch (msg) {
        case WM_CREATE:
                SetTimer(hwnd, 1, 500, timer_proc);
                return 0;
        case WM_PAINT: wm_paint(hwnd); return 0;
        case WM_SIZE: return 0;
        case WM_DESTROY: PostQuitMessage(0); return 0;
        default: return DefWindowProc(hwnd, msg, wp, lp);
        }
}

void init_wndclass(WNDCLASS *w, HINSTANCE hinstance, char *class_name)
{
        w->style = CS_HREDRAW | CS_VREDRAW;
        w->lpfnWndProc = wndproc;
        w->cbClsExtra = w->cbWndExtra = 0;
        w->hInstance = hinstance;
        w->hIcon = LoadIcon(NULL, IDI_APPLICATION);
        w->hCursor = LoadCursor(NULL, IDC_ARROW);
        w->hbrBackground = GetStockObject(WHITE_BRUSH);
        w->lpszMenuName = NULL;
        w->lpszClassName = class_name;
}

HWND create_window(HINSTANCE hinstance)
{
        WNDCLASS wndclass;
        char *class_name = "main window class";
        init_wndclass(&wndclass, hinstance, class_name);
        RegisterClass(&wndclass);
        return CreateWindowA(class_name, "TIMER TEST", WS_OVERLAPPEDWINDOW,
                        CW_USEDEFAULT, CW_USEDEFAULT, // position
                        CW_USEDEFAULT, CW_USEDEFAULT, // window size
                        NULL, /* owner window */ NULL, /* menu */
                        hinstance, NULL /* window-creation data */);
}

int WINAPI WinMain(HINSTANCE hinstance, HINSTANCE prev, PSTR cmdline,
                   int cmdshow)
{
        HWND hwnd = create_window(hinstance);
        ShowWindow(hwnd, cmdshow);
        UpdateWindow(hwnd);

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