ILE C/C++ Compiler Reference

#ifndef

The ifndef directive checks for the existence of macro definitions.

If the identifier specified is not defined as a macro, the tokens that immediately follow the condition are passed on to the compiler after a newline.

The ifndef directive has the form:

                          .----------------.
                          V                |
>>-#--ifndef--identifier----token_sequence-+-------------------><
 
 

An identifier must follow the #ifndef keyword. The following example defines MAX_LEN to be 50 if EXTENDED is not defined for the preprocessor. Otherwise, MAX_LEN is defined to be 75.

#ifndef EXTENDED
#   define MAX_LEN 50
#else
#   define MAX_LEN 75
#endif


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