header


(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​​

(function ) ​​isalpha​​

(function ) ​​isblank ​​

(function ) ​​iscntrl​​

(function ) ​​isdigit​​

(function ) ​​isgraph​​

(function ) ​​islower​​

(function ) ​​isprint​​

(function ) ​​ispunct​​

(function ) ​​isspace​​

(function ) ​​isupper​​

(function ) ​​isxdigit​​

(function )


Character conversion functions

Two functions that convert between letter cases:


​​tolower​​

(function ) ​​toupper​​

(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)



ASCII values

characters

​​iscntrl​​

​​isblank​​

​​isspace​​

​​isupper​​

​​islower​​

​​isalpha​​

​​isdigit​​

​​isxdigit​​

​​isalnum​​

​​ispunct​​

​​isgraph​​

​​isprint​​

0x00 .. 0x08

NUL, (other control codes)

x

 

 

 

 

 

 

 

 

 

 

 

0x09

tab ('\t')

x

x

x

 

 

 

 

 

 

 

 

 

0x0A .. 0x0D

(white-space control codes:'\f','\v','\n','\r')

x

 

x

 

 

 

 

 

 

 

 

 

0x0E .. 0x1F

(other control codes)

x

 

 

 

 

 

 

 

 

 

 

 

0x20

space (' ')

 

x

x

 

 

 

 

 

 

 

 

x

0x21 .. 0x2F

!"#$%&'()*+,-./

 

 

 

 

 

 

 

 

 

x

x

x

0x30 .. 0x39

0123456789

 

 

 

 

 

 

x

x

x

 

x

x

0x3a .. 0x40

:;<=>?@

 

 

 

 

 

 

 

 

 

x

x

x

0x41 .. 0x46

ABCDEF

 

 

 

x

 

x

 

x

x

 

x

x

0x47 .. 0x5A

GHIJKLMNOPQRSTUVWXYZ

 

 

 

x

 

x

 

 

x

 

x

x

0x5B .. 0x60

[\]^_`

 

 

 

 

 

 

 

 

 

x

x

x

0x61 .. 0x66

abcdef

 

 

 

 

x

x

 

x

x

 

x

x

0x67 .. 0x7A

ghijklmnopqrstuvwxyz

 

 

 

 

x

x

 

 

x

 

x

x

0x7B .. 0x7E

{|}~

 

 

 

 

 

 

 

 

 

x

x

x

0x7F

(DEL)

x

 

 

 

 

 

 

 

 

 

 

 


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​​, 

​​isgraph​​ and 

​​isprint​​ return true on these for the standard C locale on most platforms supporting extended character sets.