Name

#ifdef and #ifndef

Synopsis

The #ifdef and #ifndef directives can be used to make program text directly conditional upon whether a given macro name is defined.

Syntax:

#ifdef name
#ifndef name

The #ifdef directive is “true” if name is defined, and the #ifndef directive is “true” if name is not defined. Both require a closing #endif directive.

The following two constructions are equivalent:

#ifdef VERSION
  ...
#endif
#if defined(VERSION
  ...
#endif

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