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The ctype.h header file of the C Standard Library declares several functions that are useful for testing and mapping characters.
All the functions accepts int as a parameter, whose value must be EOF or representable as an unsigned char.
All the functions return non-zero (true) if the argument c satisfies the condition described, and zero(false) if not.
Library Functions
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. |
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 |
Alphabetic characters This is a set of Lowercase letters and Uppercase letters. |
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