TCPL/7.8.2_Character_Class_Testing_and_Conversion

7.8.2 Character Class Testing and Conversion 字符类别测试和转换函数

Several functions from <ctype.h> perform character tests and conversions. In the following, c is an int that can be represented as an unsigned char or EOF. The function returns int.

isalpha(c)      non-zero if c is alphabetic, 0 if not
isupper(c)      non-zero if c is upper case, 0 if not
islower(c)      non-zero if c is lower case, 0 if not
isdigit(c)      non-zero if c is digit, 0 if not
isalnum(c)      non-zero if isalpha(c) or isdigit(c), 0 if not
isspace(c)      non-zero if c is blank, tab, newline, return, formfeed, vertical tab
toupper(c)      return c converted to upper case
tolower(c)      return c converted to lower case

头文件<ctype.h>中定义了一些用于字符测试和转换的函数。在下面各个函数中，c是一个可表示为unsigned char类型或EOF的int对象。该函数的返回值类型为int。

isalpha(c)      若c是字母，则返回一个非0值，否则返回0
isupper(c)      若c是大写字母，则返回一个非0值，否则返回0
islower(c)      若c是小写字母，则返回一个非0值，否则返回0
isdigit(c)      若c是数字，则返回一个非0值，否则返回0
isalnum(c)      若isalpha(c)或isdigit(c)，则返回一个非0值，否则返回O
isspace(c)      若c是空格、横向制表符、换行符、回车符、换页符或纵向制表符，则返回一个非0值
toupper(c)      返回c的大写形式
tolower(c)      返回c的小写形式