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This page displays the COHERENT manpage for defined [Perform an action if a macro is defined].
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defined -- Preprocessor Operator Perform an action if a macro is defined The preprocessor directive defined determines whether a symbol is defined to the #if preprocessor directive. For example, #if defined(SYMBOL) or #if defined SYMBOL is equivalent to #ifdef SYMBOL except that it can be used in more complex expressions, such as #if defined FOO && defined BAR && FOO==10 defined is recognized only in lines beginning with #if or #elif. See Also #elif, #if, #ifdef, cpp, C preprocessor ANSI Standard, §6.8.1 Notes Note that defined is a preprocessor operator, not a preprocessor directive or a C keyword. The difference lies in the fact that you could write a function called defined() without any complaint from the C compiler; and if defined does not appear within an #if or #elif directive, the preprocessor ignores it.