Question

One of the following determines when the variable is created and destroyed and how long it will retain its value.

		linkage
		storage class
		scope
		none of the above

Answer 1

Answer :

storage class

Explanation :

The storage class of a variable determines its "lifetime", how long it remains in the computer's memory. Variables in C++ essentially fall into one of three storage classes:

• Automatic storage Automatic variables are allocated and initialized automatically when program flow enters their scope, and de-allocated automatically when program flow leaves their scope. Automatic variables are stored on the program's call stack.

  In C++, all local variables (including function and method parameters) are automatic variables by default.

• Static storage Static variables are allocated and initialized once at the beginning of program execution. They continue to exist (and retain their value) throughout the execution of the program, regardless of whether or not they are currently in scope.

  In C++, global variables are static variables by default. A local variable or class data member (but not a function or method parameter) may be made a static variable by placing the keyword static at the front of the variable declaration.

  For example, in the following function the local variable numCalls is initialized to 0 at the start of the program. It retains its value throughout the execution of the program.

  void countCalls()
     {
     static int numCalls = 0;    // Value of numCalls is retained between each function call
  
     numCalls++;
     cout << "The countCalls function has been called " << numCalls << " times\n";
     }
  

• Dynamic storage Dynamic variables are allocated at run time using the C++ operators new and new[]. Dynamic variables exist until they are explicitly de-allocated using the C++ operators delete and delete[] or the program ends. Dynamic variables are allocated from a large pool of unused memory area called the heap.