(libc.info.gz) Classification of Characters

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(libc.info.gz) Character Handling

(libc.info.gz) Case Conversion

 
 4.1 Classification of Characters
 ================================
 
 This section explains the library functions for classifying characters.
 For example, 'isalpha' is the function to test for an alphabetic
 character.  It takes one argument, the character to test, and returns a
 nonzero integer if the character is alphabetic, and zero otherwise.  You
 would use it like this:
 
      if (isalpha (c))
        printf ("The character `%c' is alphabetic.\n", c);
 
    Each of the functions in this section tests for membership in a
 particular class of characters; each has a name starting with 'is'.
 Each of them takes one argument, which is a character to test, and
 returns an 'int' which is treated as a boolean value.  The character
 argument is passed as an 'int', and it may be the constant value 'EOF'
 instead of a real character.
 
    The attributes of any given character can vary between locales.
  Locales, for more information on locales.
 
    These functions are declared in the header file 'ctype.h'.
 
  -- Function: int islower (int C)
      Preliminary: | MT-Safe | AS-Safe | AC-Safe |  POSIX Safety
      Concepts.
 
      Returns true if C is a lower-case letter.  The letter need not be
      from the Latin alphabet, any alphabet representable is valid.
 
  -- Function: int isupper (int C)
      Preliminary: | MT-Safe | AS-Safe | AC-Safe |  POSIX Safety
      Concepts.
 
      Returns true if C is an upper-case letter.  The letter need not be
      from the Latin alphabet, any alphabet representable is valid.
 
  -- Function: int isalpha (int C)
      Preliminary: | MT-Safe | AS-Safe | AC-Safe |  POSIX Safety
      Concepts.
 
      Returns true if C is an alphabetic character (a letter).  If
      'islower' or 'isupper' is true of a character, then 'isalpha' is
      also true.
 
      In some locales, there may be additional characters for which
      'isalpha' is true--letters which are neither upper case nor lower
      case.  But in the standard '"C"' locale, there are no such
      additional characters.
 
  -- Function: int isdigit (int C)
      Preliminary: | MT-Safe | AS-Safe | AC-Safe |  POSIX Safety
      Concepts.
 
      Returns true if C is a decimal digit ('0' through '9').
 
  -- Function: int isalnum (int C)
      Preliminary: | MT-Safe | AS-Safe | AC-Safe |  POSIX Safety
      Concepts.
 
      Returns true if C is an alphanumeric character (a letter or
      number); in other words, if either 'isalpha' or 'isdigit' is true
      of a character, then 'isalnum' is also true.
 
  -- Function: int isxdigit (int C)
      Preliminary: | MT-Safe | AS-Safe | AC-Safe |  POSIX Safety
      Concepts.
 
      Returns true if C is a hexadecimal digit.  Hexadecimal digits
      include the normal decimal digits '0' through '9' and the letters
      'A' through 'F' and 'a' through 'f'.
 
  -- Function: int ispunct (int C)
      Preliminary: | MT-Safe | AS-Safe | AC-Safe |  POSIX Safety
      Concepts.
 
      Returns true if C is a punctuation character.  This means any
      printing character that is not alphanumeric or a space character.
 
  -- Function: int isspace (int C)
      Preliminary: | MT-Safe | AS-Safe | AC-Safe |  POSIX Safety
      Concepts.
 
      Returns true if C is a "whitespace" character.  In the standard
      '"C"' locale, 'isspace' returns true for only the standard
      whitespace characters:
 
      '' ''
           space
 
      ''\f''
           formfeed
 
      ''\n''
           newline
 
      ''\r''
           carriage return
 
      ''\t''
           horizontal tab
 
      ''\v''
           vertical tab
 
  -- Function: int isblank (int C)
      Preliminary: | MT-Safe | AS-Safe | AC-Safe |  POSIX Safety
      Concepts.
 
      Returns true if C is a blank character; that is, a space or a tab.
      This function was originally a GNU extension, but was added in
      ISO C99.
 
  -- Function: int isgraph (int C)
      Preliminary: | MT-Safe | AS-Safe | AC-Safe |  POSIX Safety
      Concepts.
 
      Returns true if C is a graphic character; that is, a character that
      has a glyph associated with it.  The whitespace characters are not
      considered graphic.
 
  -- Function: int isprint (int C)
      Preliminary: | MT-Safe | AS-Safe | AC-Safe |  POSIX Safety
      Concepts.
 
      Returns true if C is a printing character.  Printing characters
      include all the graphic characters, plus the space (' ') character.
 
  -- Function: int iscntrl (int C)
      Preliminary: | MT-Safe | AS-Safe | AC-Safe |  POSIX Safety
      Concepts.
 
      Returns true if C is a control character (that is, a character that
      is not a printing character).
 
  -- Function: int isascii (int C)
      Preliminary: | MT-Safe | AS-Safe | AC-Safe |  POSIX Safety
      Concepts.
 
      Returns true if C is a 7-bit 'unsigned char' value that fits into
      the US/UK ASCII character set.  This function is a BSD extension
      and is also an SVID extension.
 

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(libc.info.gz) Character Handling

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