KillTimer无法删除指定定时器问题求助

我最近写了一段代码来学习SetTimer和KillTimer的用法，逻辑是这样的：在WM_CREATE消息里设置一个定时器，然后在定时器的回调函数里调用KillTimer，想让定时器只被触发一次。我还在回调函数里加了一个MessageBox，用来提示定时器被调用了，本来以为这个弹窗只会出现一次——毕竟弹完之后就会调用KillTimer关掉定时器了。

但程序的运行结果完全不符合预期，KillTimer好像根本没按要求停止定时器，反而程序一直在弹出MessageBox，停都停不下来。有没有大佬能帮我看看问题出在哪？

下面是我的代码：

#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);
        }
}

备注：内容来源于stack exchange，提问作者Limina102