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copied!<p>If you want to get low level enough to detect key up events, you should process the WM_KEYDOWN and WM_KEYUP events:</p> <ul> <li><a href="http://msdn.microsoft.com/en-us/library/ms646267%28v=vs.85%29.aspx#_win32_Keystroke_Messages" rel="noreferrer">http://msdn.microsoft.com/en-us/library/ms646267%28v=vs.85%29.aspx#_win32_Keystroke_Messages</a></li> </ul> <blockquote> <p>Pressing a key causes a WM_KEYDOWN or WM_SYSKEYDOWN message to be placed in the thread message queue attached to the window that has the keyboard focus. Releasing a key causes a WM_KEYUP or WM_SYSKEYUP message to be placed in the queue.</p> <p>Key-up and key-down messages typically occur in pairs, but if the user holds down a key long enough to start the keyboard's automatic repeat feature, the system generates a number of WM_KEYDOWN or WM_SYSKEYDOWN messages in a row. It then generates a single WM_KEYUP or WM_SYSKEYUP message when the user releases the key.</p> </blockquote> <p>To distinguish between the left and right versions of the Shift, Ctrl, or Alt keys, you have to use the <code>MapVirtualKey()</code> function or the 'extended key' bit in the lParam passed with the virtual key's message. The following function will perform that translation for you - just pass in the virtual keycode and the lParam from the message, and you'll get back the left/right specific virtual keycodes as appropriate:</p> <pre><code>WPARAM MapLeftRightKeys( WPARAM vk, LPARAM lParam) { WPARAM new_vk = vk; UINT scancode = (lParam & 0x00ff0000) >> 16; int extended = (lParam & 0x01000000) != 0; switch (vk) { case VK_SHIFT: new_vk = MapVirtualKey(scancode, MAPVK_VSC_TO_VK_EX); break; case VK_CONTROL: new_vk = extended ? VK_RCONTROL : VK_LCONTROL; break; case VK_MENU: new_vk = extended ? VK_RMENU : VK_LMENU; break; default: // not a key we map from generic to left/right specialized // just return it. new_vk = vk; break; } return new_vk; } </code></pre> <p>If the virtual keycode passed in isn't one that maps to a left/right version, the original keycode is passed back unchanged. So you can just run the <code>WM_KEYDOWN</code>/<code>WM_KEYUP</code>/<code>WM_SYSKEYDOWN</code>/<code>WM_SYSKEYUP</code> message parameters through the function whenever you need to distinguish between the left and right variants.</p>

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