cbtype.h

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#define	_U	01
#define	_L	02
#define	_N	04
#define	_S	010
#define _P	020
#define _C	040
#define	_X	0100
#define _O	0200

extern	unsigned char	_cbtype_[];	/* in /usr/src/libc/gen/ctype_.c */

#define isop(c)	((_cbtype_+1)[c]&_O)
#define	isalpha(c)	((_cbtype_+1)[c]&(_U|_L))
#define	isupper(c)	((_cbtype_+1)[c]&_U)
#define	islower(c)	((_cbtype_+1)[c]&_L)
#define	isdigit(c)	((_cbtype_+1)[c]&_N)
#define	isxdigit(c)	((_cbtype_+1)[c]&(_N|_X))
#define	isspace(c)	((_cbtype_+1)[c]&_S)
#define ispunct(c)	((_cbtype_+1)[c]&_P)
#define isalnum(c)	((_cbtype_+1)[c]&(_U|_L|_N))
#define isprint(c)	((_cbtype_+1)[c]&(_P|_U|_L|_N))
#define iscntrl(c)	((_cbtype_+1)[c]&_C)
#define isascii(c)	((unsigned)(c)<=0177)
#define toupper(c)	((c)-'a'+'A')
#define tolower(c)	((c)-'A'+'a')
#define toascii(c)	((c)&0177)