Topic       : C-Language Documentation
Author      : John Kormylo
Version     : C.HYP 1.0
Subject     : Documentation/C-Language
Nodes       : 233
Index Size  : 6362
HCP-Version : 3
Compiled on : Atari
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@lang       : en
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View Ref-File[ #define ]

  #define macro text
  #define macro(arg, ...) text arg text
  #define macro(arg, ...) text(arg)text
  #define macro(arg, ...) text ## arg
  #define macro(arg, ...) "text" # arg

where 'macro' is a macro name, 'arg' is an argument name, and 'text'
can be any combination of characters (except '#' and '\').

The '##' operator causes the surrounding blanks to be removed.
The '#' operator causes the surrounding strings to be merged 
  ('arg' must be a string constant).

Wherever the 'macro' appears in the source code, it will be replaced
by the 'text'.  Also, 'macro' will now satisfy the #ifdef directive.

Examples:

  #define DEBUG
  #define NULL 0
  #define SQUARE(x) (x) * (x)
  #define PACK_INT(a,b) ( ( ((int) (a)) << 8) | ((b) & 255) )
  #define PATH(member) "C:\FOLDER\" # member

Note: Because macros work by symbolic substitution, using '++' or
      '--' in a macro argument can have unexpected results:

      j = SQUARE(i++);   /* j = i * (i+1); i += 2; */

See also Preprocessor, Names, #undef, and Predefined Macros.