Variables and Parameters

A variable represents a storage location that has a modifiable value. A variable can be a local variable, parameter (value, ref, or out), field (instance or static), or array element.

The Stack and the Heap

The stack and the heap are the places where variables and constants reside. Each has very different lifetime semantics.

Stack

The stack is a block of memory for storing local variables and parameters. The stack logically grows and shrinks as a function is entered and exited. Consider the following method (to avoid distraction, input argument checking is ignored):

static int Factorial (int x)
{
  if (x == 0) return 1;
  return x * Factorial (x-1);
}

This method is recursive, meaning that it calls itself. Each time the method is entered, a new int is allocated on the stack, and each time the method exits, the int is deallocated.

Heap

The heap is a block of memory in which objects (i.e., reference-type instances) reside. Whenever a new object is created, it is allocated on the heap, and a reference to that object is returned. During a program’s execution, the heap starts filling up as new objects are created. The runtime has a garbage collector that periodically deallocates objects from the heap, so your computer does not run out of memory. An object is eligible for deallocation as soon as it’s not referenced by anything that’s itself alive.

Value-type instances (and object references) live wherever the variable was declared. If the instance was declared as a field within ...

Get C# 5.0 Pocket Reference now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.