Defined Operator

DEFINED OPERATOR

We have seen that we can check the existence of a macro by using #ifdef directive. However, there is another way to do the same. The alternative to #ifdef directive is to use the defined unary operator. The defined operator has one of the following forms:

defined MACRO

or

defined (MACRO)

The above expression evaluates to 1 if MACRO is defined and to o if it is not. The defined operator helps you to check for macro definitions in one concise line without having to use many #ifdef or #ifndef directives. For example, consider the following macro checks:

#ifdef MACRO1

#ifdef MACRO2

Controlled text1

#else

printf("\n MACROS not defined");

#endif

OR

#if defined (MACRO1) && defined (MACRO2)

Controlled text1

#else

printf("\n MACROS not defined");

#endif

As evident from the above example, the defined operator can be combined in any logical expression using the c logical operators. However, this operator can only be used in the evaluated expression of an #if or #elif preprocessor directive.