Programs use two different kinds of variables: static (or global) and stack variables. Static variables are assigned a fixed address. Regardless of what functions execute, a static variable always resides at the same address. Stack variables (local or auto variables in C) always belong to a specific function and are only accessible during the life of the function that declared them. The stack variables for a function are created from scratch (on the stack) each time the function runs. Depending on the stack depth when the function starts, its stack variables can very well be placed in a different location in memory.

Static variables are easy to work with but take up memory space all the time. Stack variables are temporarily allocated by the currently running function and are very convenient for temporary storage. The space allocated to a stack variable is given up and used by other functions as soon as the function that declared the variable completes. Both types of variables are necessary, and both have good and bad points.

The allocation and deallocation of stack variables is handled by code at the beginning and end of every function, called, respectively, the prolog and the epilog. This invisible code is generated by the compiler and is part of the function overhead, not part of the function s logic. In most cases, the prolog and epilog allocate and deallocate a stack frame large enough to accommodate the variables declared inside the function. The allocation...