Character Processing Functions

Non-printable/Printable Tests - iscntrl, isprint, isgraph and isspace

• int iscntrl(int c)
  • Returns a nonzero value if c is a control character, where control character may differ from machine to machine, but for the standard 128-character ASCII set, is any character with a value between 0 and 31 or a value equal to 127
• int isprint(int c)
  • Returns a nonzero value if c is a printing character, and on most implementations is the same as (iscntrl(c) ? 0 : 1).
• int isgraph(int c)
  • Returns a nonzero value if c is a visible character, that is, it returns non-zero for everything that isprint returns non-zero except a space character.
• int isspace(int c)
  • Returns a nonzero value if c is a whitespace character. In ASCII, whitespace characters are space (' '), tab ('\t'), carriage return ('\r'), newline ('\n'), vertical tab ('\v') and formfeed ('\f').

Alphabetic - isupper, islower, isalpha

• int isupper(int c)
  • Returns a nonzero value if c is one of a locale-defined set of uppercase characters, usually A through Z.
• int islower(int c)
  • Returns a nonzero value if c is one of a locale-defined set of lowercase characters, usually a through z.
• int isalpha(int c)
  • Returns a nonzero value if c is either an uppercase or lowercase character, that is, and is roughly equivalent to (islower(c) || isupper(c)).

Numeric Tests - isdigit and isxdigit

• int isdigit(int c)
  • Returns a nonzero value if c is a decimal digit (0 through 9)
• int isxdigit(int c)
  • Returns a nonzero value if c is a hexadecimal digit (0 through 9, A through F or a through f)

Alphanumeric Test - isalnum

• int isalnum(int c)
  • Returns a nonzero value if c is either a letter or a decimal digit and is roughly equivalent to (isalpha(c) || isdigit(c)).

Punctuation Test - ispunct

• int ispunct(int c)
  • Returns a nonzero value if c is a punctuation character, that is, it returns non-zero for everything that is neither a space nor a character for which isalnum returns a nonzero value.

Case Conversion - toupper and tolower

• int toupper(int c)
  • If c is a lowercase letter, the corresponding uppercase letter is returned.
  • If c is not a lowercase letter, c is returned unchanged.
  • Some locales may have lowercase characters with no corresponding uppercase letter, in which case the lowercase character is returned unchanged.
  • Pre-ANSI C implementations of toupper may not work correctly if c is not a lowercase character.
• int tolower(int c)
  • tolower is nearly identical to toupper except that uppercase characters are converted to lowercase characters.
  • All caveats which apply to toupper are equally applicable to tolower.