Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

                                             ◄Up► ◄Contents► ◄Index► ◄Back►
────────────────────────────────────────────────────────────────────────────
 
  Directive:  #ifndef
              #if !defined
 
  Syntax:     #ifndef identifier
              #if !defined (identifier)
 
  Summary:    Checks whether <identifier> is currently defined. Returns
              true (nonzero) if the definition is missing, or false (0)
              if it is present. The expression #if !defined is
              preferred for all new programs because it can be easily
              changed to check for other conditions on the same line.
 
  See also:   #define, defined, #if, #ifdef, #undef
                                    -♦-