Page 115 - DCAP408_WEB_PROGRAMMING

Unit 7: Character Sets, Fonts and the Keyboard

7.4 WM_CHAR Message Notes

WM_CHAR message is posted to the window with the keyboard focus when a WM_KEYDOWN
message is converted by the Translate Message function.

The WM_CHAR message includes the character code of the key that was pressed.
#define WM_CHAR 0x0102

7.4.1 Parameters

wParam: It is the character code of the key.
lParam: The repeat count, scan code, extended-key flag, context code, previous key-state flag,
and transition-state flag, as displayed in the following table.

Bits Meaning
0-15 The repeat count for the existing message. The value is the number of times the keystroke
is auto repeated as a consequence of the user holding down the key. If the keystroke is
held long enough, numerous messages are sent. However, the repeat count is not
cumulative.
16-23 The scan code. The value relies on the OEM.
24 Signifies whether the key is an extended key, like the right-hand ALT and CTRL keys that
appear on an enhanced 101- or 102-key keyboard. The value is 1 if it is an extended key; or
else, it is 0.
25-28 Reserved; do not use.
29 The context code. The value is 1 if the ALT key is held down while the key is pressed; or
else, the value is 0.
30 The previous key state. The value is 1 if the key is down before the message is sent, or it is
0 if the key is up.
31 The transition state. The value is 1 if the key is being released, or it is 0 if the key is being
pressed.

7.4.2 Return Value

An application should return zero if it processes this message.

Remarks

The WM_CHAR message utilizes Unicode Transformation Format (UTF)-16.
Since there is not necessarily a one-to-one correspondence among keys pressed and character
messages produced, the information in the high-order word of the lParam parameter is usually
not useful to applications. The information in the high-order word applies only to the most
recent WM_KEYDOWN message that precedes the posting of the WM_CHAR message.
For improved 101- and 102-key keyboards, extensive keys are the right ALT and the right CTRL
keys on the chief 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 divide (/) and ENTER
keys in the numeric keypad. Some other keyboards may sustain the extended-key bit in the
lParam parameter.
The WM_UNICHAR message is the similar as WM_CHAR, except it utilizes UTF-32. It is
intended to send or post Unicode characters to ANSI windows, and it can manage Unicode
additional Plane characters.

LOVELY PROFESSIONAL UNIVERSITY 109