qc.hlp (Table of Contents; Topic list)
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#ifdef
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  Directive:  #ifdef
              #if defined
 
  Syntax:     #ifdef identifier
              #if defined (identifier)
 
  Summary:    Checks to see whether <identifier> is currently defined.
              Returns true (nonzero) if it is currently defined, or
              false (0) if it is not. 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.
              For example,
 
                   #ifdef OS2
                   #ifdef PM
                   #pragma message ("OS2 and PM defined")
                   #endif
                   #endif
 
                   #if defined OS2 && defined PM
                   #pragma message ("OS2 and PM defined")
                   #endif
 
  See also:   #define, defined, #if, #ifndef, #undef
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