minix中关于如何判定一个字符的类型，如大写、小写、数字……
如果采用传统的方法，如判断一个字母大写的方法：if(c>='A' && c<'Z') return true;
但是如果判断一个字符是数字或是字母，则采用下面的代码：
if((c<'z' && c>'a') || (c<'Z' && c>'A') || (c>'0' && c<'9')) return true
如果假设更多的局限，效率明显下降
minix的做法是定义一个256元素的unsigned char _ctypes[]数组，由于8位需要8种属性分别描述，如下：#define _U 0x01 /* this bit is for upper-case letters [A-Z] */#define _L 0x02 /* this bit is for lower-case letters [a-z] */#define _N 0x04 /* this bit is for numbers [0-9] */#define _S 0x08 /* this bit is for white space \t \n \f etc */#define _P 0x10 /* this bit is for punctuation characters */#define _C 0x20 /* this bit is for control characters */#define _X 0x40 /* this bit is for hex digits [a-f] and [A-F]*/#define _PROTOTYPE(function, params) function params
判断字符函数原型：
_PROTOTYPE( int isalnum, (int _c) ); /* alphanumeric [a-z], [A-Z], [0-9] */_PROTOTYPE( int isalpha, (int _c) ); /* alphabetic */_PROTOTYPE( int iscntrl, (int _c) ); /* control characters */_PROTOTYPE( int isdigit, (int _c) ); /* digit [0-9] */_PROTOTYPE( int isgraph, (int _c) ); /* graphic character */_PROTOTYPE( int islower, (int _c) ); /* lower-case letter [a-z] */_PROTOTYPE( int isprint, (int _c) ); /* printable character */_PROTOTYPE( int ispunct, (int _c) ); /* punctuation mark */_PROTOTYPE( int isspace, (int _c) ); /* white space sp, \f, \n, \r, \t, \v*/_PROTOTYPE( int isupper, (int _c) ); /* upper-case letter [A-Z] */_PROTOTYPE( int isxdigit,(int _c) ); /* hex digit [0-9], [a-f], [A-F] */_PROTOTYPE( int tolower, (int _c) ); /* convert to lower-case */_PROTOTYPE( int toupper, (int _c) ); /* convert to upper-case */
以上函数都是通过宏定义：
#define isalnum(c) ((__ctype+1)[c]&(_U|_L|_N))#define isalpha(c) ((__ctype+1)[c]&(_U|_L))#define iscntrl(c) ((__ctype+1)[c]&_C)#define isgraph(c) ((__ctype+1)[c]&(_P|_U|_L|_N))#define ispunct(c) ((__ctype+1)[c]&_P)#define isspace(c) ((__ctype+1)[c]&_S)#define isxdigit(c) ((__ctype+1)[c]&(_N|_X))#define isdigit(c) ((unsigned) ((c)-'0') < 10)#define islower(c) ((unsigned) ((c)-'a') < 26)#define isupper(c) ((unsigned) ((c)-'A') < 26)#define isprint(c) ((unsigned) ((c)-' ') < 95)#define isascii(c) ((unsigned) (c) < 128)
minix将_ctype[]初始化为：
char __ctype[] = {0,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C|_S,_C|_S,_C|_S,_C|_S,_C|_S,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_S,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_N,_N,_N,_N,_N,_N,_N,_N,_N,_N,_P,_P,_P,_P,_P,_P,_P,_U|_X,_U|_X,_U|_X,_U|_X,_U|_X,_U|_X,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_P,_P,_P,_P,_P,_P,_L|_X,_L|_X,_L|_X,_L|_X,_L|_X,_L|_X,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_P,_P,_P,_P,_C,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,};