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NEXTKEY()
Read the pending key in the keyboard buffer
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Syntax
NEXTKEY() --> nInkeyCode
Returns
NEXTKEY() returns an integer numeric value ranging from -39 to 386 for
keyboard events and integer values from 1001 to 1007 for mouse events.
This value identifies either the key extracted from the keyboard buffer
or the mouse event that last occurred. If the keyboard buffer is empty
and no mouse events are taking place, NEXTKEY() returns zero. If SET
TYPEAHEAD is zero, NEXTKEY() always returns zero.
Description
NEXTKEY() is a function that reads the keystroke pending in the keyboard
buffer or the next mouse event without removing it. The value returned
is the INKEY() code of the key pressed--the same value as returned by
INKEY() and LASTKEY(). NEXTKEY() returns values for all ASCII
characters as well as function, Alt+function, Ctrl+function, Alt+letter,
and Ctrl+letter key combinations.
NEXTKEY() is like the INKEY() function but differs in one fundamental
respect. INKEY() removes the pending key from the keyboard buffer and
updates LASTKEY() with the value of the key. by contrast NEXTKEY()
reads, but does not remove the key from the keyboard buffer, and does
not update LASTKEY().
Since NEXTKEY() does not remove the key from the keyboard buffer, it can
be used to poll the keyboard, and then pass control to a routine that
uses a wait state or INKEY() to actually fetch the key from the buffer.
For a complete list of INKEY() codes and Inkey.ch constants, refer to
the "Clipper Inkey Codes Appendix" in the Error Messages and
Appendices Guide.
Examples
. This example places an Esc key in the keyboard buffer, and
then shows the differences between INKEY(), LASTKEY(), and NEXTKEY():
#include "Inkey.ch"
//
CLEAR TYPEAHEAD
KEYBOARD CHR(K_ESC)
//
? NEXTKEY(), LASTKEY() // Result: 27 0
? INKEY(), LASTKEY() // Result: 27 27
? NEXTKEY() // Result: 0
Files Library is EXTEND.LIB, header file is Inkey.ch.
See Also: KEYBOARD SET TYPEAHEAD
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