Question

Hi I have a file with some text in it. Is there some easy way to get the number of lines in the file without traversing through the file?

I also need to put the lines of the file into a vector. I am new to C++ but I think vector is like ArrayList in java so I wanted to use a vector and insert things into it. So how would I do it?

Thanks.

Answer 1

You would need to traverse the file to detect the number of lines (or at least call a library method that traverse the file).

Here is a sample code for parsing text file, assuming that you pass the file name as an argument, by using the getline method:

#include <string>
#include <vector>
#include <fstream>
#include <iostream>

int main(int argc, char* argv[])
{
  std::vector<std::string> lines;
  std::string line;

  lines.clear();

  // open the desired file for reading
  std::ifstream infile (argv[1], std::ios_base::in);

  // read each file individually (watch out for Windows new lines)    
  while (getline(infile, line, '\n'))
  {
    // add line to vector
    lines.push_back (line);
  }
  // do anything you like with the vector.  Output the size for example:
  std::cout << "Read " << lines.size() << " lines.\n";

  return 0;
}

Update: The code could fail for many reasons (e.g. file not found, concurrent modifications to file, permission issues, etc). I’m leaving that as an exercise to the user.