c++ fastest way to read only last line of text file?

Question

I would like to read only the last line of a text file (I\'m on UNIX, can use Boost). All the methods I know require scanning through the entire file to get the last line wh

Answer 1

Initially this was designed to read the last syslog entry. Given that the last character before the EOF is '\n' we seek back to find the next occurrence of '\n' and then we store the line into a string.

#include 
#include 

int main()
{
  const std::string filename = "test.txt";
  std::ifstream fs;
  fs.open(filename.c_str(), std::fstream::in);
  if(fs.is_open())
  {
    //Got to the last character before EOF
    fs.seekg(-1, std::ios_base::end);
    if(fs.peek() == '\n')
    {
      //Start searching for \n occurrences
      fs.seekg(-1, std::ios_base::cur);
      int i = fs.tellg();
      for(i;i > 0; i--)
      {
        if(fs.peek() == '\n')
        {
          //Found
          fs.get();
          break;
        }
        //Move one character back
        fs.seekg(i, std::ios_base::beg);
      }
    }
    std::string lastline;
    getline(fs, lastline);
    std::cout << lastline << std::endl;
  }
  else
  {
    std::cout << "Could not find end line character" << std::endl;
  }
  return 0;
}