[amp_mcq option1=”a class has been defined” option2=”a variable has been given a value” option3=”a class has no variable definitions” option4=”any objects of the class have been instantiated” correct=”option1″]
The correct answer is: A. a class has been defined.
The #ifndef directive is used to test whether a macro has been defined. If the macro has not been defined, the code inside the #ifndef block will be executed. The #ifndef directive is often used to prevent multiple definitions of a class.
Option B is incorrect because the #ifndef directive does not test whether a variable has been given a value.
Option C is incorrect because the #ifndef directive does not test whether a class has no variable definitions.
Option D is incorrect because the #ifndef directive does not test whether any objects of the class have been instantiated.