Question

I’ve heard the phrase:

“let the call stack unwind more than one level”

being mentioned in exception handling.

What does this mean?

Language in question is C#.

Thanks

Answer 1

In simplistic terms, you can think of the call stack working as follows:

• Every time a method/function is called, a “frame” is pushed onto the stack.
• Every time a method/function returns/finishes/exits, that “frame” is popped off the stack.

So, when the call stack unwinds more than one level, more than one stack frame comes off at once — like a series of nested method calls (not just a single method call) returning.

In terms of exceptions:

• Throwing an exception which is the caught within the same method will not cause the function to return prematurely, so the stack is not “unwound” any levels at all.
• Throwing an exception which is caught in the direct caller/parent method of the method that threw the exception will cause that child method to return prematurely, but not the parent method, so exactly one stack frame will be popped.
• Throwing an exception which is not caught until it has caused numerous method calls to exit prematurely will “let the call stack unwind more than one level.”

Apologies for being a bit fast-and-loose with the terminology.