Page 113 - DCAP408_WEB_PROGRAMMING

Unit 7: Character Sets, Fonts and the Keyboard

When the window procedure obtains the WM_KEYDOWN message, it should inspect the virtual- Notes
key code that accompanies the message to find out how to process the keystroke. The virtual-
key code is included in the wParamparameter of the message.
The lParam parameter of a keystroke message includes additional data regarding the keystroke
that produced the message. The following table displays the additional keystroke data that is
needed by the lParam parameter.
Data Description
Context code The value is 1 if the ALT key was pressed or 0 if the pressed key was released.
Previous key state The value is 1 if the pressed key was down before or 0 if the pressed key was
up before. The value is 1 for WM_KEYDOWN and WM_SYSKEYDOWN
keystroke messages that were produced by automatic repeat functionality.
Repeat count States the number of times that the keystroke was repeated as a result of the
user holding down the key.
Scan code Provides the hardware-dependent key scan code.
Transition state The value is 1 if the key was released or if the key was pressed.

Usually, an application processes only the keystrokes that are produced by noncharacter keys.

Example: The following code example displays the window procedure framework that
a usual application uses to obtain and process keystroke messages.
case WM_KEYDOWN:
switch (wParam)
{
case VK_HOME:
// Insert code here to process the HOME key
// ...
break;

case VK_END:
// Insert code here to process the END key
// ...
break;

case VK_INSERT:
// Insert code here to process the INS key
// ...
break;

case VK_F2:
// Insert code here to process the F2 key
// ...
break;

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