Handy Vector-printing Template Function, C++

Often when working with C++ I find myself wanting to quickly plot the contents of a vector with something like matplotlib. When working in an interpertive Python environment such as IPython or an IPython notebook, quickly generating plots for "sanity checks" frequently only involves a few lines of code. For example:

# some programming....

In [60]: print v[0:10]
[ 0.          0.09983342  0.19866933  0.29552021  0.38941834  0.47942554
  0.56464247  0.64421769  0.71735609  0.78332691]

In [61]: plt.plot(v)

In [62]:

# keep working away...

For a similar experience when working with C++ I have found it handy to be able to dump the contents of a vector to std::cout in a format that can be directly copy/pasted into a Python script or interperter. To that end, I have written a template function that will take a vector and create a comma separated string using the vector's contents.

Below is a sample program demonstrating the function. An alternative version boost::lexical_cast shown but commented out. While boost::lexical_cast is more consise, there is less formatting control.

// sample.cpp

// To compile and run:
//     $ g++ sample.cpp
//     $ ./a.out 
//     vector_of_ints = [0, 0, 0, 0, 0]
//     vector_of_floats = [0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00]

#include <iostream>
#include <iomanip>
#include <string>
#include <sstream>
#include <vector>
//#include <boost/lexical_cast.hpp>

/** Template function that generates a comma separated string from the contents of
*  a vector. Elements are separated by a comma and a space for readability.
*/
template<typename T>
std::string vec2csv(const std::vector<T>& vec) {
  std::string s;
  for (typename std::vector<T>::const_iterator it = vec.begin(); it != vec.end(); ++it) {

    // Simpler, but requires boost and offers minimal formatting control
    //s += boost::lexical_cast<std::string>(*it);

    // Doesn't require boost, offers more formatting control
    std::ostringstream ss;
    ss << std::fixed << std::setprecision(2);
    ss << *it;
    s += ss.str();
    s += ", ";

  }
  if (s.size() >= 2) {   // clear the trailing comma, space
    s.erase(s.size()-2);
  }
  return s;
}

int main() {

  std::vector<int> v_ints(5);
  std::vector<float> v_flts(10);

  std::cout << "vector_of_ints = [" << vec2csv(v_ints) << "]" << std::endl;
  std::cout << "vector_of_floats = [" << vec2csv(v_flts) << "]" << std::endl;

  return 0;
}

Inversion Labs