sprintf returning std::string

str_printf.hpp

/* from http://www.ohfuji.name/?p=4 */
#include <cstdio>
#include <cstdlib>
#include <cstdarg>
#include <vector>
#include <string>
#include <stdexcept>

std::string str_printf(const char* const format, ...)
{
  int bufsize = 1024;
  std::vector<char> buff(bufsize);
  va_list args;

  /// first try
  va_start(args, format);
  int vssize = vsnprintf( &buff[0], bufsize, format, args);
  va_end(args);

  /// if bufsize is sufficient, return
  if(vssize>=0 && vssize<bufsize) {
    buff.resize(vssize);
    return std::string(buff.begin(), buff.end());
  }

  if(vssize<0) throw std::runtime_error(format);

  /// resize and retry
  buff.resize(vssize + 1);

  va_start(args, format);
  vssize = vsnprintf(&buff[0], vssize + 1, format, args);
  va_end(args);

  if(vssize<0) throw std::runtime_error(format);
  buff.resize(vssize);

  return std::string(buff.begin(), buff.end());
}