Function Call Stack and Activation Records
To understand how ‘C’ executes function calls, we first need to consider a data-structure (i.e., collection of related data items) known as a stack. A stack is analogous to a pile of dishes.
To understand is place on the pile, it’s normally placed at the top (referred to as pushing the dish onto the stack). Similarly, when a dish is removed from the pile, it’s always removed from the top (referred to as popping the dish off the stack).
Stacks are known as last-in first-out (LIFO) data structures-the last item pushed (inserted) on the stack is the first item popped (removed) from stack.
When a program calls a function, the called function must know how to return to its caller, so the return address of the calling functions is pushed onto the program execution stack (sometimes referred to as the function call stack).
If a series of function calls occur, the successive return addresses are pushed onto the stack is last-in, first-out order, so that each function can return to its caller.
The program execution stack also contains the memory for the local variables used in each invocation of a function during a programs execution.
This data, stored as a portion of the program execution stack, is known as the activation record or stack frame of the function call.
When a function call is made, the activation record for that function call is pushed onto the program execution stack.
When the function returns to its caller, the activation record for this function call is popped off the stack and those local variables are no longer known to the program.
