SendMessage用法问题

C/C++ code

#include "stdafx.h"#include "windows.h"#pragma comment(lib,"user32.lib")int _tmain(int argc, _TCHAR* argv[]){    HWND hWnd = FindWindow(NULL, _T("xxyy.txt - 记事本"));    if (hWnd != NULL)    {         printf("%s\n", "11111111111");                        SendMessage(hWnd, WM_KEYDOWN, VK_TAB, 0);    // 消息1    }    printf("%s\n", "2222222222222222");    return 0;}