Move pointer to next line in .txt file

I'm trying to select a value at random from a .txt document. Each value is on a separate line (I understand that the computer interprets that as Value 1\nValue 2\n Value3).

Example.txt

Code:

---

WORD | SUBJECT
WORD | SUBJECT
WORD | SUBJECT
WORD | SUBJECT

---

I can pull the same word and subject without a problem. Is there anyway to randomly set the pointer to begin on a different line of the .txt file? Short of going through and finding all the pointer positions?

I've already initialized rand() to a truly random number using srand(time(NULL)). I just can't figure out a way to move to a random line and return the information.

To sum it up...is there anyway to move the pointer "vertically" by identifying '\n' chars?

> Is there anyway to randomly set the pointer to begin on a different line of the .txt file?
> Short of going through and finding all the pointer positions?
That is exactly what you have to do with a text file - read the whole thing and build an index of all the start of line positions.

Then you can randomly seek to a line and read it.

Or consider reading the whole file into a std::vector< std::string >
Then pick one from that.

Ok...I wrote it all down and it made a little more sense...

I read it all into a buffer, then go through and see how many '\n' characters there are. But how can I declare the positions after the \n's as possible start points for the input from the file?

Well in C terms, you do

ftell() to find the current file pointer, store this in an index
fgets() to read a line

Do that until you've indexed the whole file.

Then to pick a line, you fseek() to a position in the index and do fgets() to read your random line.

Here's what I have right now:

Code:

---

void Player::GetWord()
{
    srand( (time(NULL) );
    int NumLines(0), RandNum, length;
    ifstream File;
    char * buffer;

    File.open("example.txt")
    if(File.is_open())
    {
          File.seekg(0, ios::end);
          length = File.tellg();
          File.seekg(0, ios::beg);

          buffer = new char [length];

          File.read(buffer, length);

          for(int x(0); x < length; x++)
          {
              if(buffer[x] == '\n')
                    NumLines++;
          }

          RandNum = rand()%NumLines;
    }
}

---

Is there a way to flag the \n chars? Or should I just record their position in an array? In your example, are you suggesting making an array of strings, each with a different line of the file?

Hmm...I guess I could store them as a bidimensional array of strings....hmmmmmmmm

I will suggest you use a vector of strings if the file is not too big

Code:

---

// reading a text file
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;

int main () {
  string line;
  ifstream myfile ("example.txt");
  vector<string> v;
  if (myfile.is_open())
  {
    while (! myfile.eof() )
    {
      getline (myfile,line);
      v.push_back(line);

    }
    myfile.close();

  // you have the vector of lines in your file
  // get which ever line you want by line number
  for(unsigned int i = 0; i < v.size(); ++i)
    cout<<v.at(i)<<"\n";

  }

  else cout << "Unable to open file";

  return 0;
}

---