C++ Converting Vector items to single String Error?

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?

Curse C++ and its implicit int->char conversions. Something like key += std::to_string(temp.at(i)); might suit you better. Also, "" + temp.at(0) evaluates to a random address, not a string. — Qaz
– Qaz, Commented Oct 29, 2012 at 3:05

user500944 · Accepted Answer · 2012-10-29 03:11:14Z

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);

answered Oct 29, 2012 at 3:11

user500944

Sign up to request clarification or add additional context in comments.

7 Comments

Qaz Over a year ago

I don't think compilers issue warnings for implicit int->char conversions.

user500944 Over a year ago

Actually it seems to depend on the warning level

Qaz Over a year ago

I get nothing from GCC 4.7.2 or VS11 (both my own with warnings cranked up) with this: liveworkspace.org/code/f12876f52980fd7b67a52fe164ec8408

user500944 Over a year ago

Have you tried setting the warning level to 4 in Visual Studio?

Qaz Over a year ago

Indeed I have :/ That implicit conversion is really one we could do without.

|

Collectives™ on Stack Overflow

C++ Converting Vector items to single String Error?

1 Answer 1

7 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

7 Comments

Your Answer

Sign up or log in

Post as a guest

Related