iscntrl.c

标准c库代码,可以应用于各个系统提供了大量的基本函数

/*
FUNCTION
	<<iscntrl>>---control character predicate

INDEX
	iscntrl

ANSI_SYNOPSIS
	#include <ctype.h>
	int iscntrl(int <[c]>);

TRAD_SYNOPSIS
	#include <ctype.h>
	int iscntrl(<[c]>);

DESCRIPTION
<<iscntrl>> is a macro which classifies ASCII integer values by table
lookup.  It is a predicate returning non-zero for control characters, and 0 
for other characters.  It is defined only when <<isascii>>(<[c]>) is
true or <[c]> is EOF. 

You can use a compiled subroutine instead of the macro definition by
undefining the macro using `<<#undef iscntrl>>'.

RETURNS
<<iscntrl>> returns non-zero if <[c]> is a delete character or ordinary
control character (<<0x7F>> or <<0x00>>--<<0x1F>>).

PORTABILITY
<<iscntrl>> is ANSI C.

No supporting OS subroutines are required.
*/

#include <_ansi.h>
#include <ctype.h>



#undef iscntrl
int
_DEFUN(iscntrl,(c),int c)
{
	return((_ctype_ + 1)[c] & _C);
}