#include <windows.h>
    #include <vector>

    struct EnumWindowsCallbackArgs {
        EnumWindowsCallbackArgs(DWORD p) : pid(p) { }
        const DWORD pid;
        std::vector<HWND> handles;
    };

    static BOOL CALLBACK EnumWindowsCallback(HWND hnd, LPARAM lParam)
    {
        EnumWindowsCallbackArgs *args = (EnumWindowsCallbackArgs *)lParam;

        DWORD windowPID;
        (void)::GetWindowThreadProcessId(hnd, &windowPID);
        if (windowPID == args->pid) {
            args->handles.push_back(hnd);
        }

        return TRUE;
    }

    std::vector<HWND> getToplevelWindows()
    {
        EnumWindowsCallbackArgs args(::GetCurrentProcessId());
        if (::EnumWindows(&EnumWindowsCallback, (LPARAM)&args) == FALSE) {
            // XXX Log error here
            return std::vector<HWND>();
        }
        return args.handles;
    }