表达式评估-避免StackOverflow异常

Question

I had been fiddling around to build my own expression evaluator and landed up at this issue i am curious about.

I have used 2 ways of evaluating a string expression. One method uses a Binary tree.

When i enter an expression string of length greater than (approx.) 42000, i get a stackoverflow exception.

However the same does not happen if i evaluate the same expression string (even of much longer length) with this function (my second implementation)

Now i would prefer to stick to the Binary tree method - is there a way i can fix the Stack overflow exception, ie i can avoid my Stack overflow in recursion or is there a way to find when the Stack will actually overflow? If not, how can i actually at least warn the user before even the expression starts getting evaluated that a Stack overflow can happen?

Answer 1

Honestly, your best bet is to use the second method. While a recursion is usable here, from an algorithm standpoint, the stack method that you provided is more correct - Mainly because your binary tree method doesn't have a way to deal with unary operators (as far as I can tell, at least) (eg, ++i).

As for your first question, there isn't really a way to tell if something will throw a stack overflow exception from just input. Your best bet would be to just wrap the first call to the recursive method in a try/catch, and explicitly catch the StackOverflowException, and return a valid error message to the user.

Also, keep in mind, you could theoretically move the binary tree implementation to use a stack object similar to number 2, if you wanted. Although you'd still have to redesign the method to use your stack instead of the application's stack.