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The framework calls this member function when a nonsystem key is pressed.

afx_msg void OnKeyDown(
   UINT nChar,
   UINT nRepCnt,
   UINT nFlags 



Specifies the virtual key code of the given key. For a list of of standard virtual key codes, see Winuser.h


Repeat count (the number of times the keystroke is repeated as a result of the user holding down the key).


Specifies the scan code, key-transition code, previous key state, and context code, as shown in the following list:

Value Description


Scan code (OEM-dependent value).


Extended key, such as a function key or a key on the numeric keypad (1 if it is an extended key).


Not used.


Used internally by Windows.


Context code (1 if the ALT key is held down while the key is pressed; otherwise 0).


Previous key state (1 if the key is down before the call, 0 if the key is up).


Transition state (1 if the key is being released, 0 if the key is being pressed).

For a WM_KEYDOWN message, the key-transition bit (bit 15) is 0 and the context-code bit (bit 13) is 0.

A nonsystem key is a keyboard key that is pressed when the ALT key is not pressed or a keyboard key that is pressed when CWnd has the input focus.

Because of auto-repeat, more than one OnKeyDown call may occur before an OnKeyUp member function call is made. The bit that indicates the previous key state can be used to determine whether the OnKeyDown call is the first down transition or a repeated down transition.

For IBM Enhanced 101- and 102-key keyboards, enhanced keys are the right ALT and the right CTRL keys on the main section of the keyboard; the INS, DEL, HOME, END, PAGE UP, PAGE DOWN, and arrow keys in the clusters to the left of the numeric keypad; and the slash (/) and ENTER keys in the numeric keypad. Some other keyboards may support the extended-key bit in nFlags.


This member function is called by the framework to allow your application to handle a Windows message. The parameters passed to your function reflect the parameters received by the framework when the message was received. If you call the base-class implementation of this function, that implementation will use the parameters originally passed with the message and not the parameters you supply to the function.