performance check for getline with various buffer sizes

buffertest.cpp

#include <string>
#include <iostream>
#include <fstream>
#include <cstdlib>

// usage:
// time ./a.out [1G|1M|default] filename > /dev/null

void error(const char* p, const char* p2 = "")
{
  std::cerr << p << ' ' << p2 << '\n';
  std::exit(1);
}

int main(int argc, char* argv[])
{
  if (argc != 3) error ("wrong number of arguments");

  std::ifstream from(argv[2]);
  if (!from) error("cannot open input file", argv[2]);

  const int M = 1024 * 1024;
  const int G = 1024 * 1024 * 1024;

  char* internal_buf;
  char* buf;
  int size = 4096;
  if (std::string(argv[1]) == std::string("1M")) {
    size = M;
  } else if (std::string(argv[1]) == std::string("1G")) {
    size = G;
  }
  internal_buf = new char[size];
  buf = new char[size];
  from.rdbuf()->pubsetbuf(internal_buf, size);
  
  std::string s;

  while (!from.eof()) {
    from.read(buf, size);
    
    //    std::getline(from, s);
    //    std::cout <<  << std::endl;
  }

  if (!from.eof()) error("something strange happend");
}