This header declares a set of functions to classify and transform individual
characters.
These functions take the int equivalent of one character
as parameter and return an int that can either be another
character or a value representing a boolean value:
an int value of 0 means false, and
an int value different from 0represents
true.
There are two sets of functions:
They check whether the character passed as parameter belongs to a certain
category:
Two functions that convert between letter cases:
For the first set, here is a map of how the original 127-character ASCII
set is considered by each function (an x indicates that the function returns
true on that character)
| ASCII values | characters | iscntrl | isblank | isspace | isupper | islower | isalpha | isdigit | isxdigit | isalnum | ispunct | isgraph | isprint |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0x00 .. 0x08 | NUL, (other control codes) | x | |||||||||||
| 0x09 | tab (‘\t‘) | x | x | x | |||||||||
| 0x0A .. 0x0D | (white-space control codes:‘\f‘,‘\v‘,‘\n‘,‘\r‘) | x | x | ||||||||||
| 0x0E .. 0x1F | (other control codes) | x | |||||||||||
| 0x20 | space (‘ ‘) | x | x | x | |||||||||
| 0x21 .. 0x2F | !"#$%&‘()*+,-./ | x | x | x | |||||||||
| 0x30 .. 0x39 | 0123456789 | x | x | x | x | x | |||||||
| 0x3a .. 0x40 | :;<=>?@ | x | x | x | |||||||||
| 0x41 .. 0x46 | ABCDEF | x | x | x | x | x | x | ||||||
| 0x47 .. 0x5A | GHIJKLMNOPQRSTUVWXYZ | x | x | x | x | x | |||||||
| 0x5B .. 0x60 | [\]^_` | x | x | x | |||||||||
| 0x61 .. 0x66 | abcdef | x | x | x | x | x | x | ||||||
| 0x67 .. 0x7A | ghijklmnopqrstuvwxyz | x | x | x | x | x | |||||||
| 0x7B .. 0x7E | {|}~ | x | x | x | |||||||||
| 0x7F | (DEL) | x |
The characters in the extended character set (above 0x7F) may belong to
diverse categories depending on the locale and the platform. As a general
rule, ispunct, isgraph and isprint return true on these
for the standard C locale on most platforms supporting extended character
sets.
cctype 头文件所包含的函数主要用来测试字符值。
| isalnum(c) | 假如c是字母或数字，则为true |
| isalpah(c) | 假如c是字母，则为true |
| iscntrl(c) | 假如c是控制字符，则为true |
| isdigit(c) | 假如c是数字，则为true |
| isgraph(c) | 假如c不是空格，则为true |
| islower(c) | 假如c是小写字母，则为true |
| isprint(c) | 假如c是可打印的字符，则为true |
| ispunct(c) | 假如c是标点符号，则为true |
| isspace(c) | 假如c是空白字符，则为true |
| isupper(c) | 假如c是大写字母，则为true |
| isxdigit(c) | 假如c是十六进制数，则为true |
| tolower(c) | 假如c是大写字母，则返回小写字母形式，否则返回c。 |
| toupper(c) | 假如c是小写字母，则返回大些字母形式，否则返回c。 |
原文地址：http://www.cnblogs.com/leadtheway/p/3737019.html
