CODEWITHSUNDEEP
c++callstack
Vikram Singh
Vikram Singh

Reputation: 435

How does the call stack unwinding process exactly work, for function calls? - C++

I am solving the TowerOfHanoi problem, using stacks in STL (C++). But I am not sure why I am getting this warning at line 6703:

Warning C26444

When I get this warning, I don't get the intended result on running the program. The program shows no output on the console window and the console window simply says - "Press any key to continue..."

But, when I put a return statement in front of line 6703, the warning goes away and, I get the correct result on the output console window:

Appending return, solves the issue

And, following is the output on the console, when I append return in front of the function call (at line 6703) -

Correct output, when I append return in front of the function

Why do I have to append return in front of the function call, for it to work correctly?

If we look at the call stack, there are three call stacks created: 1. One for main 2. The second for towerOfHanoi(stack1,stack2,stack3, 3) 3. The third for towerOfHanoi(stack1,stack2,stack3, 2)

After that, stack unwinding process begins - 3. towerOfHanoi(stack1,stack2,stack3, 2) returns stack3 to towerOfHanoi(stack1,stack2,stack3, 3) 2. Now, towerOfHanoi(stack1,stack2,stack3, 3) in turn returns stack3 to main()

Am I correct on how the stack unwinding process is going on? And, return is essential at line 6703: return towerOfHanoi(stack1, stack2, stack3, n - 1) - because if it is absent, we will fail to return the stack3 to main? -

StackFrame unwinding process

Can you please explain me the stack frame unwinding process better?

Upvotes: 0

Views: 213

Answers (1)

idris
idris

Reputation: 588

towerOfHanoi(stack1,stack2,stack3, 2) returns stack3 to towerOfHanoi(stack1,stack2,stack3, 3) beacuse of 

if (n == 2) {
    return stack3;
}

but

towerOfHanoi(stack1,stack2,stack3, 3) doesnt return anything to main. Because you didnt provided a return statement at the end function.

Upvotes: 2

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