Question

So I have a function, where KaylesPosition is a class with a vector<int> called piles:

// Produces a key to compare itself to equivalent positions     
std::string KaylesPosition::makeKey(){
  std::vector<int> temp(piles.size());
  for (int i = 0;i<piles.size();i++){
    temp[i]=piles[i];
  }

  std::sort (temp.begin(),temp.end());
  std::string key = "" + temp.at(0);
  for (int i=1 ; i<temp.size() ; i++){
    key.push_back('.');
    key.push_back(temp.at(i));
  }

  return key;
}

My expected output should be all of the elements in piles in order, separated by periods. However instead, I get key return as “_M_range_check”. I have tried this using std::string.append() and I get either an empty string or a period. How do I get this function to return a string of all of the values in piles as expected?

Answer 1

The problem seems to be here:

key.push_back(temp.at(i));

You are trying to append an integer to a string without getting the string representation of the integer first. Try replacing that line with:

key += std::to_string(temp.at(i)); // This will only work if your compiler supports C++11

If your compiler doesn’t support C++11, try this (don’t forget to #include <sstream>):

std::ostringstream o;
o << temp.at(i);
key += o.str();

Or, if you have the option to use Boost (http://boost.org/ ), try its lexical_cast:

key += boost::lexical_cast<std::string>(temp.at(i));

The reason this code compiled in the first place, is because push_back accepts a char as its parameter and you’re passing an int which gets converted to char (although I would expect a warning from the compiler in this case).

P.S.: Same applies for the line

  std::string key = "" + temp.at(0);