atoi on a character array with lots of integers

Question

I have a code in which the character array is populated by integers (converted to char arrays), and read by another function which reconverts it back to integers. I have use

Answer 1

There is absolutely no reason for the Karma/Qi text version to be any slower than the STL version. I improved @sehe implementation of the Karma/Qi text version to reflect that claim.

The following Boost Karma/Qi text version is more than twice as fast as the STL version:

#include 
#include 
#include 
#include 
#include 
#include 

namespace ascii = boost::spirit::ascii;
namespace qi = boost::spirit::qi;
namespace karma = boost::spirit::karma;
namespace phoenix = boost::phoenix;


template 
void generate_numbers(OutputIterator& sink, const std::vector& v){

  using karma::int_;
  using karma::generate_delimited;
  using ascii::space;

  generate_delimited(sink, *int_, space, v);
}

template 
void parse_numbers(Iterator first, Iterator last, std::vector& v){

  using qi::int_;
  using qi::phrase_parse;
  using ascii::space;
  using qi::_1;
  using phoenix::push_back;
  using phoenix::ref;

  phrase_parse(first, last, *int_[push_back(ref(v), _1)], space);
}

int main(int argc, char* argv[]){

  static boost::mt19937 rng(0); // make test deterministic
  std::vector data;
  data.resize(2 << 24);
  std::generate(data.begin(), data.end(), rng);

  std::string astext;
  std::back_insert_iterator out(astext);
  generate_numbers(out, data);

  //std::cout << astext << std::endl;

  std::string::const_iterator begin(astext.begin()), end(astext.end());
  std::vector clone;
  parse_numbers(begin, end, clone);

  //verify that clone now contains the original random data:
  //std::copy(clone.begin(), clone.end(), std::ostream_iterator(std::cout, ","));

  return 0;
}