The GetAsyncKeyState function determines whether a key is up or down at the time the function is called, and whether the key was pressed after a previous call to GetAsyncKeyState.
SHORT GetAsyncKeyState(
int vKey // virtual-key code
);
Windows NT: You can use left- and right-distinguishing constants to specify certain keys. See the Remarks section for further information.
If the function succeeds, the return value specifies whether the key was pressed since the last call to GetAsyncKeyState, and whether the key is currently up or down. If the most significant bit is set, the key is down, and if the least significant bit is set, the key was pressed after the previous call to GetAsyncKeyState. The return value is zero if a window in another thread or process currently has the keyboard focus.
Windows 95: Windows 95 does not support the left- and right-distinguishing constants. If you call GetAsyncKeyState with these constants, the return value is zero.
The GetAsyncKeyState function works with mouse buttons. However, it checks on the state of the physical mouse buttons, not on the logical mouse buttons that the physical buttons are mapped to. For example, the call GetAsyncKeyState(VK_LBUTTON) always returns the state of the left physical mouse button, regardless of whether it is mapped to the left or right logical mouse button. You can determine the system's current mapping of physical mouse buttons to logical mouse buttons by calling
GetSystemMetrics(SM_SWAPBUTTON)
which returns TRUE if the mouse buttons have been swapped.
You can use the virtual-key code constants VK_SHIFT, VK_CONTROL, and VK_MENU as values for the vKey parameter. This gives the state of the shift, ctrl, or alt keys without distinguishing between left and right.
Windows NT: You can use the following virtual-key code constants as values for vKey to distinguish between the left and right instances of those keys.
| Code | Meaning |
|---|---|
| VK_LSHIFT | VK_RSHIFT |
| VK_LCONTROL | VK_RCONTROL |
| VK_LMENU | VK_RMENU |
These left- and right-distinguishing constants are only available when you call the GetKeyboardState, SetKeyboardState, GetAsyncKeyState, GetKeyState, and MapVirtualKey functions.
Windows CE: The GetAsyncKeyState function supports the left and right virtual key constants, so you can determine whether the left key or the right key was pressed. These constants are VK_LCONTROL, VK_RCONTROL, VK_LMENU, VK_RMENU, VK_LSHIFT, and VK_RSHIFT.
The least significant bit of the return value is not valid in Windows CE, and should be ignored.
GetAsyncKeyState will return the current key state even if a window in another thread or process currently has the keyboard focus.
You can also use the VK_LBUTTON virtual-key code constant to determine the state of the stylus tip, (up/down), on the touch-screen.
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winuser.h.
Import Library: Use user32.lib.
Keyboard Input Overview, Keyboard Input Functions, GetKeyboardState, GetKeyState, GetSystemMetrics, MapVirtualKey, SetKeyboardState