The null directive (#)

The null directive performs no action. It consists of a single # on a line of its own.

The null directive should not be confused with the # operator or the character that starts a preprocessor directive.

In the following example, if MINVAL is a defined macro name, no action is performed. If MINVAL is not a defined identifier, it is defined 1.

#ifdef MINVAL
  #
#else
  #define MINVAL 1
#endif

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