C Standard Library Reference Guide (2) ctype.h

2. ctype.h

The character class header file is used to test characters and convert characters. A control character that references another character that is not part of a printable character set. In the ASCII character set, all characters 0x0 to 0x1f and 0x7f (delete key) are control characters, printable characters from 0x20 (spaces) to 0x7e (wave numbers).

Function:

Isalnum ();

Isalpha ();

Iscntrl ();

IsDigit ();

Isgraph ();

Islower ();

Isprint ();

Ispunct ();

Isspace ();

Isupper ();

Isxdigit ();

ToLower ();

ToUpper ();

2.1. Is ... Functions

Statement:

int isalnum (intcharacter);

int Isalpha (intcharacter);

int Iscntrl (intcharacter);

int isdigit (intcharacter);

int isgraph (intcharacter);

int islower (intcharacter);

int isprint (intcharacter);

int ispunct (intcharacter);

int isspace (intcharacter);

int Isupper (intcharacter);

int isxdigit (int character);

Functions such as "is ..." test the character in the instrumentation parameter and return a non-0 value (TRUE) when the character satisfies the condition. Returns 0 (false) if it is not satisfied.

Conditions:

Isalnum	English letters (A to Z, or A to Z), or Arabic numerals (0 to 9)
Isalpha	English letters (A to Z, or A to Z)
Iscntrl	Control characters (0x00 to 0x1f, or 0x7f)
IsDigit	Arabic numerals (0 to 9)
Isgraph	Any printable character other than a space (0x21 to 0x7e)
Islower	Lowercase letters (A to Z)
Isprint	printable characters (0x20 to 0x7e)
Ispunct	Punctuation (except spaces, printable characters outside of album)
Isspace	White space characters (spaces, tabs, carriage returns, line breaks, portrait tabs, page breaks, form feeds)
Isupper	Uppercase letters (A to Z)
Isxdigit	Hexadecimal number (0 to 9,a to F, or a to f)