B.2 Character Class Tests: <ctype.h>

The header <ctype.h> declares functions for testing characters. For each function, the argument list is an int, whose value must be EOF or representable as an unsigned char, and the return value is an int. The functions return non-zero (true) if the argument c satisfies the condition described, and zero if not.

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isalnum(c)isalpha(c) or isdigit(c) is true

isalpha(c)isupper(c) or islower(c) is true

iscntrl(c)control character

isdigit(c)decimal digit

isgraph(c)printing character except space

islower(c)lower-case letter

isprint(c)printing character including space

ispunct(c)printing character except space or letter or digit

isspace(c)space, formfeed, newline, carriage return, tab, vertical tab

isupper(c)upper-case letter

isxdigit(c)hexadecimal digit

In the seven-bit ASCII character set, the printing characters are 0x20 (' ') to 0x7E ('-'); the control characters are 0 NUL to 0x1F (US), and 0x7F (DEL).

In addition, there are two functions that convert the case of letters:

 

int tolower(c)convert c to lower case

int toupper(c)convert c to upper case

If c is an upper-case letter, tolower(c) returns the corresponding lower-case letter, toupper(c) returns the corresponding upper-case letter; otherwise it returns c.