Stack Frames

As each function is called, it may, in turn, call other functions, which may, in turn, call other functions—all before any of the functions return. Each function eventually must return control to the function that called it. So, somehow, we must keep track of the return addresses that each function needs to return control to the function that called it. The function call stack is the perfect data structure for handling this information. Each time a function calls another function, an entry is pushed onto the stack. This entry, called a stack frame or an activation record, contains the return address that the called function needs in order to return to the calling function. It also contains some additional information we’ll soon discuss. If the called function returns, instead of calling another function before returning, the stack frame for the function call is popped, and control transfers to the return address in the popped stack frame.

The beauty of the call stack is that each called function always finds the information it needs to return to its caller at the top of the call stack. And, if a function makes a call to another function, a stack frame for the new function call is simply pushed onto the call stack. Thus, the return address required by the newly called function to return to its caller is now located at the top of the stack.