c++ recursion exits without obvious reason

Question

I wrote a function using a recursion. While testing it, it turned out, that the function is killed without any obvious reason, while the recursion is still running.

To test this, I wrote an infinite recursion.

On my PC this function quits after about 2 seconds and the last output is about 327400. The last number isn't always the same.

I am using Ubuntu Lucid Lynx, the GCC compiler and Eclipse as IDE. If somebody has an idea what the problem is and how I can prevent the program from exiting I would be really pleased.

#include <iostream>

void rek(double x){
    std::cout << x << std::endl;
    rek(x + 1);
}

int main(int argc, char **argv) {
    rek(1);
}

Answer 1

You are most likely overflowing the stack, at which point your program will be summarily killed. The depth of the stack will always limit the amount you can recurse, and if you are hitting that limit, it means your algorithm needs to change.

Answer 2

I think you are right in expecting the code to run forever, as explained in

How do I check if gcc is performing tail-recursion optimization?

your code should be able to run for ever and ever, if gcc is performing tail recursion. On my machine it looks like -O3 actually makes gcc generate tail calls and actually flatten the stack. :-)

I surgest you set the optimize flag to O2 or O3.

Answer 3

You are causing a stack overflow (running out of stack space) because you don't provide an exit condition.

void rek(double x){
   if(x > 10)
      return;
   std::cout << x << std::endl;
   rek(x + 1);
}