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#ifndef              Preprocessing Directive              #ifndef




Include code conditionally


The preprocessing directive #ifndef checks whether identifier has
been defined as a macro name.  If identifier has _n_o_t been defined
as  a macro,  then  the preprocessor  includes  group within  the
program, up  to the next  #elif, #else, or  #endif directive.  If
identifier has been defined, however, then group is skipped.

An  #ifndef directive  can  be followed  by any  number of  #elif
directives, by one #else directive, and by one #elif directive.

***** See Also *****

#elif, #else, #endif, #if, #ifndef, C preprocessor, defined









































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