整理：<cctype>（<ctype.h>）

短命女 2022-07-20 12:29 62阅读 0赞

int isalpha(int ch)  若ch是字母('A'-'Z','a'-'z')返回非0值,否则返回0  
int isalnum(int ch)  若ch是字母('A'-'Z','a'-'z')或数字('0'-'9')  
                     返回非0值,否则返回0  
int isascii(int ch)  若ch是字符(ASCII码中的0-127)返回非0值,否则返回0  
int iscntrl(int ch)  若ch是作废字符(0x7F)或普通控制字符(0x00-0x1F)  
                     返回非0值,否则返回0  
int isdigit(int ch)  若ch是数字('0'-'9')返回非0值,否则返回0  
int isgraph(int ch)  若ch是可打印字符(不含空格)(0x21-0x7E)返回非0值,否则返回0  
int islower(int ch)  若ch是小写字母('a'-'z')返回非0值,否则返回0  
int isprint(int ch)  若ch是可打印字符(含空格)(0x20-0x7E)返回非0值,否则返回0  
int ispunct(int ch)  若ch是标点字符(0x00-0x1F)返回非0值,否则返回0  
int isspace(int ch)  若ch是空格(' '),水平制表符(' '),回车符(' '),  
                     走纸换行('f'),垂直制表符('v'),换行符(' ')  
                     返回非0值,否则返回0  
int isupper(int ch)  若ch是大写字母('A'-'Z')返回非0值,否则返回0  
int isxdigit(int ch) 若ch是16进制数('0'-'9','A'-'F','a'-'f')返回非0值,  
                     否则返回0  
int tolower(int ch)  若ch是大写字母('A'-'Z')返回相应的小写字母('a'-'z')  
int toupper(int ch)  若ch是小写字母('a'-'z')返回相应的大写字母('A'-'Z')

ctype.h的C标准库的头文件中提供的声明几个有用的函数测试和字符映射。

所有的功能都接受int作为参数，其值必须是EOF或为unsigned char表示。

所有函数返回的参数c非零（true），如果满足条件。否则返回0。

## 库函数 ##

以下是在头文件ctype.h中定义的函数：

<table style="font-family:Helvetica,Arial,sans-serif; font-size:16px; border-collapse:collapse; border-spacing:0px; max-width:100%; margin:8px 0px; padding:0px; border-color:rgb(214,214,214); vertical-align:top; color:rgb(0,0,0); line-height:22px; border-style:solid; width:560px; background-color:rgb(247,247,247)"> 
 <tbody style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; margin:0px; padding:0px"> 
 <tr style="margin:0px; padding:0px"> 
 <th style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; margin:0px; border-collapse:collapse; border:1px solid rgb(214,214,214); line-height:1.42857; vertical-align:top; width:22px; background-color:rgb(238,238,238)"> S.N.</th> 
 <th style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; margin:0px; border-collapse:collapse; border:1px solid rgb(214,214,214); line-height:1.42857; vertical-align:top; background-color:rgb(238,238,238)"> 函数及说明</th> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 1</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> int isalnum(int c) 该函数检查传递的字符是否是字母数字。</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 2</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> int isalpha(int c) 该函数是否传递的字符是字母。</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 3</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> int iscntrl(int c) 该函数是否传递的字符是控制字符。</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 4</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> int isdigit(int c) 该函数是否传递的字符是十进制数字。</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 5</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> int isgraph(int c) 该函数是否传递的字符的图形表示，使用的语言环境。</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 6</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> int islower(int c) 该函数检查传递的字符是否是小写字母。</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 7</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> int isprint(int c) 该函数检查传递的字符是否是可打印的。</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 8</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> int ispunct(int c) 该函数检查传递的字符是否是标点符号。</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 9</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> int isspace(int c) 该函数检查传递的字符是否是空白。</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 10</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> int isupper(int c) 该函数检查传递的字符是否是大写字母。</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 11</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> int isxdigit(int c) 该函数检查传递的字符是否是十六进制数字。</td> 
 </tr> 
 </tbody> 
</table>

该库还包含两个转换函数，也接受并返回一个“整数”

## 字符类 ##

<table style="font-family:Helvetica,Arial,sans-serif; font-size:16px; border-collapse:collapse; border-spacing:0px; max-width:100%; margin:8px 0px; padding:0px; border-color:rgb(214,214,214); vertical-align:top; color:rgb(0,0,0); line-height:22px; border-style:solid; width:560px; background-color:rgb(247,247,247)"> 
 <tbody style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; margin:0px; padding:0px"> 
 <tr style="margin:0px; padding:0px"> 
 <th style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; margin:0px; border-collapse:collapse; border:1px solid rgb(214,214,214); line-height:1.42857; vertical-align:top; width:22px; background-color:rgb(238,238,238)"> S.N.</th> 
 <th style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; margin:0px; border-collapse:collapse; border:1px solid rgb(214,214,214); line-height:1.42857; vertical-align:top; background-color:rgb(238,238,238)"> 字符类说明</th> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 1</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> Digits A set of whole numbers { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 }</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 2</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> Hexadecimal digits This is the set of { 0 1 2 3 4 5 6 7 8 9 A B C D E F a b c d e f }</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 3</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> Lowercase letters This is a set of { a b c d e f g h i j k l m n o p q r s t u v w x y z }</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 4</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> Uppercase letters A set of whole numbers {A B C D E F G H I J K L M N O P Q R S T U V W X Y Z }</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 5</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> Letters This is a set of lowercase letters and uppercase letters</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 6</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> Alphanumeric characters This is a set of Digits, Lowercase letters and Uppercase letters</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 7</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> Punctuation characters This is a set of ! " # $ % &amp; ' ( ) * + , - . / : ; &lt; = &gt; ? @ [ ] ^ _ ` { | } ~</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 8</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> Graphical characters This is a set of Alphanumeric characters and Punctuation characters.</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 9</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> Space characters This is a set of tab, newline, vertical tab, form feed, carriage return, and space.</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 10</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> Printable characters This is a set of Alphanumeric characters, Punctuation characters and Space characters.</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 11</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> Control characters In ASCII, these characters have octal codes 000 through 037, and 177 (DEL).</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 12</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> Blank characters These are space and tab.</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> 13</td> 
 <td style="font-family:'Open Sans',Arial,'Hiragino Sans GB','Microsoft YaHei',微软雅黑,STHeiti,'WenQuanYi Micro Hei',SimSun,sans-serif,sans-serif; font-size:11pt; padding:5px; line-height:1.42857; vertical-align:top; border:1px solid rgb(214,214,214); margin:0px; border-collapse:collapse"> Alphabetic characters This is a set of Lowercase letters and Uppercase letters.</td> 
 </tr> 
 </tbody> 
</table>

C++ 语言下 
头文件：\#include <cctype> 
说明： 字符处理库 
功能一：字符测试 
1> 函数原型均为int isxxxx(int) 
2> 参数为int, 任何实参均被提升成整型 
3> 只能正确处理处于\[0, 127\]之间的值 
![3.png][]  
功能二：字符映射 
1> 函数原型为int toxxxx(int) 
2> 对参数进行检测, 若符合范围则转换, 否则不变 
![2.png][]

备注说明：C语言下的此类功能头文件是<ctype.h> 
以下是<cctype>头文件的声明：

// cctype standard header
 #pragma once
 #ifndef _CCTYPE_
 #define _CCTYPE_
 #include <yvals.h>
 
 #ifdef _STD_USING
 #undef _STD_USING
 #include <ctype.h>
 #define _STD_USING
 #else /* _STD_USING */
 #include <ctype.h>
 #endif /* _STD_USING */
 #ifndef RC_INVOKED
 #if _GLOBAL_USING
 _STD_BEGIN
 using ::isalnum; using ::isalpha; using ::iscntrl;
 using ::isdigit; using ::isgraph; using ::islower;
 using ::isprint; using ::ispunct; using ::isspace;
 using ::isupper; using ::isxdigit; using ::tolower;
 using ::toupper;
 
 _STD_END
 #endif /* _GLOBAL_USING */
 #endif /* RC_INVOKED */
 	/* remove any (improper) macro overrides */
 #undef isalnum
 #undef isalpha
 #undef isblank
 #undef iscntrl
 #undef isdigit
 #undef isgraph
 #undef islower
 #undef isprint
 #undef ispunct
 #undef isspace
 #undef isupper
 #undef isxdigit
 #undef tolower
 #undef toupper
 #endif /* _CCTYPE_ */
 /*
 * Copyright (c) 1992-2006 by P.J. Plauger. ALL RIGHTS RESERVED.
 * Consult your license regarding permissions and restrictions.
 V5.02:0009 */

ASCII码字符检测结果表 下图为ASCII字符检测结果表格，画X的表示“是”（即真，返回值非0）

<table style="border:1px solid silver; border-collapse:collapse; word-break:break-word; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif"> 
 <tbody> 
 <tr> 
 <th style="border:1px solid silver; border-collapse:collapse; padding:3px">ASCII values</th> 
 <th style="border:1px solid silver; border-collapse:collapse; padding:3px">characters</th> 
 <th style="border:1px solid silver; border-collapse:collapse; padding:3px"><a href="http://www.cplusplus.com/iscntrl" style="color:rgb(51,102,153); text-decoration:none; background-color:rgb(255,255,255)" rel="nofollow">iscntrl</a></th> 
 <th style="border:1px solid silver; border-collapse:collapse; padding:3px"><a href="http://www.cplusplus.com/isblank" style="color:rgb(51,102,153); text-decoration:none; background-color:rgb(255,255,255)" rel="nofollow">isblank</a></th> 
 <th style="border:1px solid silver; border-collapse:collapse; padding:3px"><a href="http://www.cplusplus.com/isspace" style="color:rgb(51,102,153); text-decoration:none; background-color:rgb(255,255,255)" rel="nofollow">isspace</a></th> 
 <th style="border:1px solid silver; border-collapse:collapse; padding:3px"><a href="http://www.cplusplus.com/isupper" style="color:rgb(51,102,153); text-decoration:none; background-color:rgb(255,255,255)" rel="nofollow">isupper</a></th> 
 <th style="border:1px solid silver; border-collapse:collapse; padding:3px"><a href="http://www.cplusplus.com/islower" style="color:rgb(51,102,153); text-decoration:none; background-color:rgb(255,255,255)" rel="nofollow">islower</a></th> 
 <th style="border:1px solid silver; border-collapse:collapse; padding:3px"><a href="http://www.cplusplus.com/isalpha" style="color:rgb(51,102,153); text-decoration:none; background-color:rgb(255,255,255)" rel="nofollow">isalpha</a></th> 
 <th style="border:1px solid silver; border-collapse:collapse; padding:3px"><a href="http://www.cplusplus.com/isdigit" style="color:rgb(51,102,153); text-decoration:none; background-color:rgb(255,255,255)" rel="nofollow">isdigit</a></th> 
 <th style="border:1px solid silver; border-collapse:collapse; padding:3px"><a href="http://www.cplusplus.com/isxdigit" style="color:rgb(51,102,153); text-decoration:none; background-color:rgb(255,255,255)" rel="nofollow">isxdigit</a></th> 
 <th style="border:1px solid silver; border-collapse:collapse; padding:3px"><a href="http://www.cplusplus.com/isalnum" style="color:rgb(51,102,153); text-decoration:none; background-color:rgb(255,255,255)" rel="nofollow">isalnum</a></th> 
 <th style="border:1px solid silver; border-collapse:collapse; padding:3px"><a href="http://www.cplusplus.com/ispunct" style="color:rgb(51,102,153); text-decoration:none; background-color:rgb(255,255,255)" rel="nofollow">ispunct</a></th> 
 <th style="border:1px solid silver; border-collapse:collapse; padding:3px"><a href="http://www.cplusplus.com/isgraph" style="color:rgb(51,102,153); text-decoration:none; background-color:rgb(255,255,255)" rel="nofollow">isgraph</a></th> 
 <th style="border:1px solid silver; border-collapse:collapse; padding:3px"><a href="http://www.cplusplus.com/isprint" style="color:rgb(51,102,153); text-decoration:none; background-color:rgb(255,255,255)" rel="nofollow">isprint</a></th> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x00 .. 0x08</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">NUL, (other control codes)</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x09</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">tab ('\t')</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x0A .. 0x0D</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">(white-space control codes:'\f','\v','\n','\r')</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x0E .. 0x1F</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">(other control codes)</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x20</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">space (' ')</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x21 .. 0x2F</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">!"#$%&amp;'()*+,-./</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x30 .. 0x39</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0123456789</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x3a .. 0x40</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">:;&lt;=&gt;?@</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x41 .. 0x46</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">ABCDEF</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x47 .. 0x5A</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">GHIJKLMNOPQRSTUVWXYZ</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x5B .. 0x60</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">[\]^_`</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x61 .. 0x66</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">abcdef</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x67 .. 0x7A</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">ghijklmnopqrstuvwxyz</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x7B .. 0x7E</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">{|}~</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">0x7F</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">(DEL)</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">x</td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px"> </td> 
 <td style="border:1px solid silver; border-collapse:collapse; padding:3px">&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

C++ reference上的：

header

# <cctype> (ctype.h) #

Character handling functions

This header declares a set of functions to classify and transform individual characters.

### Functions ###

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:

#### Character classification functions ####

They check whether the character passed as parameter belongs to a certain category:

[**isalnum**][isalnum]

Check if character is alphanumeric  (function )

[**isalpha**][isalpha]

Check if character is alphabetic  (function )

[**isblank **][isblank]

Check if character is blank  (function )

[**iscntrl**][iscntrl]

Check if character is a control character  (function )

[**isdigit**][isdigit]

Check if character is decimal digit  (function )

[**isgraph**][isgraph]

Check if character has graphical representation  (function )

[**islower**][islower]

Check if character is lowercase letter  (function )

[**isprint**][isprint]

Check if character is printable  (function )

[**ispunct**][ispunct]

Check if character is a punctuation character  (function )

[**isspace**][isspace]

Check if character is a white-space  (function )

[**isupper**][isupper]

Check if character is uppercase letter  (function )

[**isxdigit**][isxdigit]

Check if character is hexadecimal digit  (function )

#### Character conversion functions ####

Two functions that convert between letter cases:

[**tolower**][tolower]

Convert uppercase letter to lowercase  (function )

[**toupper**][toupper]

Convert lowercase letter to uppercase  (function )

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)

<table style="font-size:12px; color:black; border-collapse:collapse"> 
 <tbody> 
 <tr> 
 <th style="border:1px solid black; background:rgb(240,240,240)">ASCII values</th> 
 <th style="border:1px solid black; background:rgb(240,240,240)">characters</th> 
 <th style="border:1px solid black; background:rgb(240,240,240)"><a href="http://www.cplusplus.com/iscntrl" style="text-decoration:none; color:rgb(0,0,112)" rel="nofollow">iscntrl</a></th> 
 <th style="border:1px solid black; background:rgb(240,240,240)"><a href="http://www.cplusplus.com/isblank" style="text-decoration:none; color:rgb(0,0,112)" rel="nofollow">isblank</a></th> 
 <th style="border:1px solid black; background:rgb(240,240,240)"><a href="http://www.cplusplus.com/isspace" style="text-decoration:none; color:rgb(0,0,112)" rel="nofollow">isspace</a></th> 
 <th style="border:1px solid black; background:rgb(240,240,240)"><a href="http://www.cplusplus.com/isupper" style="text-decoration:none; color:rgb(0,0,112)" rel="nofollow">isupper</a></th> 
 <th style="border:1px solid black; background:rgb(240,240,240)"><a href="http://www.cplusplus.com/islower" style="text-decoration:none; color:rgb(0,0,112)" rel="nofollow">islower</a></th> 
 <th style="border:1px solid black; background:rgb(240,240,240)"><a href="http://www.cplusplus.com/isalpha" style="text-decoration:none; color:rgb(0,0,112)" rel="nofollow">isalpha</a></th> 
 <th style="border:1px solid black; background:rgb(240,240,240)"><a href="http://www.cplusplus.com/isdigit" style="text-decoration:none; color:rgb(0,0,112)" rel="nofollow">isdigit</a></th> 
 <th style="border:1px solid black; background:rgb(240,240,240)"><a href="http://www.cplusplus.com/isxdigit" style="text-decoration:none; color:rgb(0,0,112)" rel="nofollow">isxdigit</a></th> 
 <th style="border:1px solid black; background:rgb(240,240,240)"><a href="http://www.cplusplus.com/isalnum" style="text-decoration:none; color:rgb(0,0,112)" rel="nofollow">isalnum</a></th> 
 <th style="border:1px solid black; background:rgb(240,240,240)"><a href="http://www.cplusplus.com/ispunct" style="text-decoration:none; color:rgb(0,0,112)" rel="nofollow">ispunct</a></th> 
 <th style="border:1px solid black; background:rgb(240,240,240)"><a href="http://www.cplusplus.com/isgraph" style="text-decoration:none; color:rgb(0,0,112)" rel="nofollow">isgraph</a></th> 
 <th style="border:1px solid black; background:rgb(240,240,240)"><a href="http://www.cplusplus.com/isprint" style="text-decoration:none; color:rgb(0,0,112)" rel="nofollow">isprint</a></th> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x00 .. 0x08</td> 
 <td style="border:1px solid black">NUL, (other control codes)</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x09</td> 
 <td style="border:1px solid black">tab ('\t')</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x0A .. 0x0D</td> 
 <td style="border:1px solid black">(white-space control codes:'\f','\v','\n','\r')</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x0E .. 0x1F</td> 
 <td style="border:1px solid black">(other control codes)</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x20</td> 
 <td style="border:1px solid black">space (' ')</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x21 .. 0x2F</td> 
 <td style="border:1px solid black">!"#$%&amp;'()*+,-./</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x30 .. 0x39</td> 
 <td style="border:1px solid black">0123456789</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x3a .. 0x40</td> 
 <td style="border:1px solid black">:;&lt;=&gt;?@</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x41 .. 0x46</td> 
 <td style="border:1px solid black">ABCDEF</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x47 .. 0x5A</td> 
 <td style="border:1px solid black">GHIJKLMNOPQRSTUVWXYZ</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x5B .. 0x60</td> 
 <td style="border:1px solid black">[\]^_`</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x61 .. 0x66</td> 
 <td style="border:1px solid black">abcdef</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x67 .. 0x7A</td> 
 <td style="border:1px solid black">ghijklmnopqrstuvwxyz</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x7B .. 0x7E</td> 
 <td style="border:1px solid black">{|}~</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">x</td> 
 </tr> 
 <tr> 
 <td style="border:1px solid black">0x7F</td> 
 <td style="border:1px solid black">(DEL)</td> 
 <td style="border:1px solid black">x</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 <td style="border:1px solid black">&nbsp;</td> 
 </tr> 
 </tbody> 
</table>

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][ispunct 1],  [isgraph][isgraph 1] and  [isprint][isprint 1] return true on these for the standard C locale on most platforms supporting extended character sets.

几个程序实例：

/*转自http://blog.csdn.net/lion_hbeu/article/details/23912551*/
 #include <iostream>
 #include <cctype>
 #include <cstdio>
 using namespace std;
 void printHead();
 int main()
 {
 int choice;
 char str_ch[50];
 char str_ch1[50];
 cout<<"input your choice,(0:大小写转换测试,1:打印ASCII字符检测结果表)\n";
 cin>>choice;
 if(choice == 0)
 {
 cout<<"input a string\n";
 cin>>str_ch;
 cout<<"源字符串："<<str_ch<<endl;
 int len = sizeof(str_ch);
 for(int i =0;i<len;i++)
 str_ch1[i] = tolower(str_ch[i]);
 cout<<"小写字符串："<<str_ch1<<endl;
 for(int i =0;i<len;i++)
 str_ch1[i] =toupper(str_ch[i]);
 cout<<"大写字符串："<<str_ch1<<endl;
 
 }
 else if(choice == 1)
 {
 printHead();
 for(int i=0;i<=127;i++)
 {
 printf("0x%02x%6d",i,i);
 if(i>=8&&i<=13 || i==127 )
 {
 printf("%10s","");
 }
 else
 printf("%10c",i);
 (isalnum(i)!=0)?printf("%10s","Y"):printf("%10s","N");
 (isalpha(i)!=0)?printf("%10s","Y"):printf("%10s","N");
 (isblank(i)!=0)?printf("%10s","Y"):printf("%10s","N");
 (iscntrl(i)!=0)?printf("%10s","Y"):printf("%10s","N");
 (isdigit(i)!=0)?printf("%10s","Y"):printf("%10s","N");
 (isgraph(i)!=0)?printf("%10s","Y"):printf("%10s","N");
 (islower(i)!=0)?printf("%10s","Y"):printf("%10s","N");
 (isprint(i)!=0)?printf("%10s","Y"):printf("%10s","N");
 (ispunct(i)!=0)?printf("%10s","Y"):printf("%10s","N");
 (isspace(i)!=0)?printf("%10s","Y"):printf("%10s","N");
 (isupper(i)!=0)?printf("%10s","Y"):printf("%10s","N");
 (isxdigit(i)!=0)?printf("%10s","Y"):printf("%10s","N");
 printf("\n");
 
 }
 }
 return 0;
 }
 void printHead()
 {
 printf("%10s","value");
 printf("%10s","chara");
 printf("%10s","isalnum");
 printf("%10s","isalpha");
 printf("%10s","isblank");
 printf("%10s","iscntrl");
 printf("%10s","isdigit");
 printf("%10s","isgraph");
 printf("%10s","islower");
 printf("%10s","isprint");
 printf("%10s","ispunct");
 printf("%10s","isspace");
 printf("%10s","isupper");
 printf("%10s","isxdigit");
 printf("\n");
 }

/*转自http://blog.csdn.net/gyysmall/article/details/12650937*/
 //用循环判断ASCII从0~127之间的字符类型
 /*
 cctype中的常用函数
 函数名称 返回值
 isalnum() 如果参数是字母数字，即字母或者数字，函数返回true
 isalpha() 如果参数是字母，函数返回true
 iscntrl() 如果参数是控制字符，函数返回true
 isdigit() 如果参数是数字（0－9），函数返回true
 isgraph() 如果参数是除空格之外的打印字符，函数返回true
 islower() 如果参数是小写字母，函数返回true
 isprint() 如果参数是打印字符（包括空格），函数返回true
 ispunct() 如果参数是标点符号，函数返回true
 isspace() 如果参数是标准空白字符，如空格、换行符、水平或垂直制表符，函数返回true
 isupper() 如果参数是大写字母，函数返回true
 isxdigit() 如果参数是十六进制数字，即0－9、a－f、A－F，函数返回true
 tolower() 如果参数是大写字符，返回其小写，否则返回该参数
 toupper() 如果参数是小写字符，返回其大写，否则返回该参数
 */
 #include <iostream>
 #include <cctype>
 using namespace std;
 int main()
 {
 	unsigned char c='\0';
 	for(;(int)c<=127;c++)
 	{
 		cout<<"ASCII为 "<<(int)c<<" 的字符为 ";
 		if(iscntrl(c))//判断是否为控制字符
 		{	cout<<(iscntrl(c)?"控制字符 ":""); 
 		 cout<<(isspace(c)?"标准空白字符，如空格、换行符、水平或垂直制表符":"");		
 		}
 		else //非控制字符
 		{			
 cout<<c<<" ";
 			cout<<(isprint(c)?"打印字符(包括空格) ":""); 
 			cout<<(isgraph(c)?"除空格之外的打印字符 ":"");
 			cout<<(isalnum(c)?"字母数字 ":"");
 			cout<<(isalpha(c)?"字母 ":""); 
 			cout<<(islower(c)?"小写字母 ":"");
 			cout<<(isupper(c)?"大写字母 ":""); 
 			cout<<(isdigit(c)?"数字(0-9) ":"");
 			cout<<(isxdigit(c)?"十六进制数字(0-9,A-F,a-f) ":"");			 
 			cout<<(ispunct(c)?"标点符号 ":"");
 		}
 		cout<<endl;
 		//cout<<"============================================="<<endl; 
 	}
 	return 0;
 }

[3.png]: /images/20220719/8625a3aae8574b11bb7c32dfdaa0d381.png
[2.png]: /images/20220719/5d26494f8c6b4176bc8cc4d4a01aad82.png
[isalnum]: http://www.cplusplus.com/reference/cctype/isalnum/
[isalpha]: http://www.cplusplus.com/reference/cctype/isalpha/
[isblank]: http://www.cplusplus.com/reference/cctype/isblank/
[iscntrl]: http://www.cplusplus.com/reference/cctype/iscntrl/
[isdigit]: http://www.cplusplus.com/reference/cctype/isdigit/
[isgraph]: http://www.cplusplus.com/reference/cctype/isgraph/
[islower]: http://www.cplusplus.com/reference/cctype/islower/
[isprint]: http://www.cplusplus.com/reference/cctype/isprint/
[ispunct]: http://www.cplusplus.com/reference/cctype/ispunct/
[isspace]: http://www.cplusplus.com/reference/cctype/isspace/
[isupper]: http://www.cplusplus.com/reference/cctype/isupper/
[isxdigit]: http://www.cplusplus.com/reference/cctype/isxdigit/
[tolower]: http://www.cplusplus.com/reference/cctype/tolower/
[toupper]: http://www.cplusplus.com/reference/cctype/toupper/
[ispunct 1]: http://www.cplusplus.com/ispunct
[isgraph 1]: http://www.cplusplus.com/isgraph
[isprint 1]: http://www.cplusplus.com/isprint