问题
RAWINPUT provides two flags (RI_KEY_E0 and RI_KEY_E1) to check whether the left or right version of a key is pressed. This works great for CTRL, but not for left and right shift. In fact, the flags are the same for both, and the VKey is also the same (VK_SHIFT). How can I find out which shift was pressed? I'm working on Windows 7. Interestingly, the flags/vkey values are exactly the same no matter which shift key I'm pressing.
回答1:
Windows 7, and I only get VK_SHIFT, never the L/R variants
Which is part of the explanation why this doesn't work the way you think it should do. There's ancient history behind this. The keyboard controller was redesigned for the IBM AT, again for the Enhanced keyboard. It started sending out 0xe0 and 0xe1 prefixes for keys that were added to the keyboard layout. Like the right Ctrl and Alt keys.
But keyboards always had two shift keys. The original IBM PC didn't consider them special keys, they simply have a different scan code. Which was maintained in later updates. Accordingly, you don't get the RI_KEY_E0 or E1 flags for them. You have to distinguish them by the RAWKEYBOARD.MakeCode value. The left shift key has makecode 0x2a, the right key is 0x36.
Note that the left Ctrl and Alt keys don't have the flags either. They match the corresponding keys on the old PC keyboard layout. The description of the flags in the MSDN Library article is not very accurate.
来源：https://stackoverflow.com/questions/5920301/distinguish-between-left-and-right-shift-keys-using-rawinput