Power set code showing segmentation fault

Question

A recursive code to find power set of string is showing error and out of memory.
void recur(string a,string b,int i=0) // Recursive fun 
{ 
  int n=a.size();
  if(i==n)         //returns if becomes equal to the size of  array
  {
    cout<<b<<endl;
    return ;
  }
  recur(a,b,i++); //calls without append
  recur(a,b+a[i],i++); //calls with append
}

IlCapitano · Answer

i++ doesn't do what you want it to do in this context, it increments the variable i and returns the value before the increment.  For example
int i = 0;
cout << i++; // prints 0
cout << i;   // prints 1

You could use pre-increment like ++i, which evaluates to the value after the increment.
Also for recur(a, b + a[i], ++i);, the evaluation order of the parameters is unspecified, so the value of a[i] is unspecified.  I suggest not using increment operators at all in this case, as it just makes the code harder to read.

largest_prime_is_463035818 · Answer

If you call the function as recur(a,b); then in this line
recur(a,b,i++); //calls without append

i is still 0. That line will call the function again with exact same parameters and you get a stackoverflow due to infininte recursion.

Power set code showing segmentation fault

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