C Standard Library 简明教程

C Library - <ctype.h>

C 标准库的 ctype.h 头文件声明了几个用于测试和映射字符的有用函数。

The ctype.h header file of the C Standard Library declares several functions that are useful for testing and mapping characters.

所有函数都接受 int 作为参数,其值必须是 EOF 或可以表示成无符号字符。

All the functions accepts int as a parameter, whose value must be EOF or representable as an unsigned char.

如果参数 c 满足所描述的条件,所有函数都会返回非零(真),不满足则返回零(假)。

All the functions return non-zero (true) if the argument c satisfies the condition described, and zero(false) if not.

Library Functions

ctype.h 中定义的函数如下:

Following are the functions defined in the header ctype.h −

Sr.No.

Function & Description

1

int isalnum(int c)This function checks whether the passed character is alphanumeric.

2

int isalpha(int c)This function checks whether the passed character is alphabetic.

3

int iscntrl(int c)This function checks whether the passed character is control character.

4

int isdigit(int c)This function checks whether the passed character is decimal digit.

5

int isgraph(int c)This function checks whether the passed character has graphical representation using locale.

6

int islower(int c)This function checks whether the passed character is lowercase letter.

7

int isprint(int c)This function checks whether the passed character is printable.

8

int ispunct(int c)This function checks whether the passed character is a punctuation character.

9

int isspace(int c)This function checks whether the passed character is white-space.

10

int isupper(int c)This function checks whether the passed character is an uppercase letter.

11

int isxdigit(int c)This function checks whether the passed character is a hexadecimal digit.

12

int isblank(int c)This function checks whether the passed character is a blank character.

库中还包含两个接受和返回“int”的转换函数。

The library also contains two conversion functions that accepts and returns an "int".

Sr.No.

Function & Description

1

int tolower(int c)This function converts uppercase letters to lowercase.

2

int toupper(int c)This function converts lowercase letters to uppercase.

Character Classes

Sr.No.

Character Class & Description

1

Digits This is a set of whole numbers { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 }.

2

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 }.

3

Lowercase letters This is a set of lowercase letters { 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 }.

4

Uppercase letters This is a set of uppercase letters {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 }.

5

Letters This is a set of lowercase and uppercase letters.

6

Alphanumeric characters This is a set of Digits, Lowercase letters and Uppercase letters.

7

Punctuation characters This is a set of ! " # $ % & ' ( ) * + , - . / : ; < = > ? @ [ \ ] ^ _ ` {

} ~

8

Graphical characters This is a set of Alphanumeric characters and Punctuation characters.

9

Space characters This is a set of tab, newline, vertical tab, form feed, carriage return, and space.

10

Printable characters This is a set of Alphanumeric characters, Punctuation characters and Space characters.

11

Control characters In ASCII, these characters have octal codes 000 through 037, and 177 (DEL).

12

Blank characters These are spaces and tabs.

13