Question

There are sooo many posts about converting from int to string but they all really involve either just printing to the screen, or using ostringstream.

I was using ostringstream, but my company doesnt want me to use any streams because it has horrid runtimes.

I was doing this in a C++ file.

my issue is that i was going to, over the course of execution create millions of streams, write to the buffers, and then copy content into a string, as such:

ostringstream OS;
os << "TROLOLOLOLOL";
std::string myStr = os.str();

There is redundancy as it is making this buffer then copying it all over. UGH!

Answer 1

In C++11:

string s = std::to_string(42);

I did a benchmark a couple of weeks ago, and got those results (using clang and libc++ shipped with current Xcode):

stringstream took 446ms
to_string took 203ms
c style took 170ms

With the following code:

#include <iostream>
#include <chrono>
#include <sstream>
#include <stdlib.h>

using namespace std;

struct Measure {
  chrono::time_point<chrono::system_clock> _start;
  string _name;

  Measure(const string& name) : _name(name) {
    _start = chrono::system_clock::now();
  }

  ~Measure() {
    cout << _name << " took " << chrono::duration_cast<chrono::milliseconds>(chrono::system_clock::now() - _start).count() << "ms" << endl;
  }
};



int main(int argc, const char * argv[]) {
  int n = 1000000;
  {
    Measure m("stringstream");
    for (int i = 0; i < n; ++i) {
      stringstream ss;
      ss << i;
      string s = ss.str();
    }
  }
  {
    Measure m("to_string");
    for (int i = 0; i < n; ++i) {
      string s = to_string(i);
    }
  }
  {
    Measure m("c style");
    for (int i = 0; i < n; ++i) {
      char buff[50];
      snprintf(buff, 49, "%d", i);
      string s(buff);
    }
  }
  return 0;
}