用GetKeyState判断指定按键是否按下
SHORT GetKeyState(int nVirtKey /* virtual-key code,eg.VK_F1 */);
//If the high-order bit is 1, the key is down; otherwise, it is up.
//If the low-order bit is 1, the key is toggled.
//例如：
GetKeyState(VK_MENU) & 0x8000
//Alt按下
GetKeyState(VK_CONTROL) & 0x8000
//Ctrl按下
文章来自：http://www.cnblogs.com/dgx/p/5491561.html