ctype.h Header File

Header File Index

Routines for checking and changing character types

 Functions
_tolower
Translates uppercase characters to lowercase.
_toupper
Translates uppercase characters to lowercase.
isalnum
Checks whether a character is an alphanumeric.
isalpha
Checks whether a character is a letter.
isascii
Checks whether a character is an ASCII character.
iscntrl
Checks whether a character is a control character.
isdigit
Checks whether a character is a digit.
isextalnum
Checks whether a character is an extended alphanumeric.
isextlower
Checks whether a character is a lowercase, including foreign ones.
isextpunct
Checks whether a character is an extended punctuation character.
isextupper
Checks whether a character is an uppercase, including foreign ones.
isfrgn
Checks whether a character is a foreign letter.
isfrgnalnum
Checks whether a character is a foreign letter which is valid in a variable name.
isfrgnlower
Checks whether a character is a foreign lowercase.
isfrgnupper
Checks whether a character is a foreign uppercase.
isgraph
Checks whether a character is a graph character.
isGreek
Checks whether a character is a Greek letter.
islower
Checks whether a character is a lowercase.
isprint
Checks whether a character is a printing character.
ispunct
Checks whether a character is a punctuation character.
isspace
Checks whether a character is a white space.
isupper
Checks whether a character is an uppercase.
isxdigit
Checks whether a character is a hex digit.
toascii
Translates characters to ASCII format.
toextlower
Translates characters to lowercase, including foreign ones.
toextupper
Translates characters to uppercase, including foreign ones.
tolower
Translates characters to lowercase.
toupper
Translates characters to uppercase.

Note: All of these functions are inline functions which are implemented using GNU C smart macros (except the simplest ones, which are ordinary macros). Some of them expand to relatively large code, so if you call any of them more than twice in a program, it will be a good idea to define an ordinary function which calls this macro. For example, if you want to call isxdigit more than twice, define the following to save memory:

int _isxdigit(int c)
{
  return isxdigit (c);
}
Then call _isxdigit instead.