defined operator

defined operator

Tests whether a macro is defined

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 defined(   identifier   ) defined   identifier   

The unary operator defined( identifier ) (also written as defined identifier , without the parentheses) evaluates to 1 if identifier is a known macro name at the point of the defined operator, or if it is not known. The operator is evaluated only in the argument to an #if or #elif directive.

The behavior is undefined if the defined operator is used in any other way, or if the token defined results from macro expansion.

See Also

#define directive, #elif directive, #if directive, #ifdef directive, # ifndef directive, #undef directive