Inputting file by dropping it on executable.

[EvanEjk]

I made a program that inputs a file, and outputs another. To do this I used:

fileIn.open("fileIn.txt");
ofstream fileOut ("fileOut.txt");

Using this way to input a file the name has to be fileIn.txt, and be in the same directory as the program.

Is there a way using C++ to make it so you can drop a file with any name on the program, and the program will assign it to fileIn?

[Duthomhas]

The way to do it is to parametrize your program on an istream, and choose based upon the arguments given to your program. For example:

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int run( istream& ins )
  {
  string s;
  unsigned n = 1;

  while (getline( ins, s ))
    {
    n++;
    }
  cout << n << " lines\n";

  return 0;
  }

int main( int argc, char** argv )
  {
  if (argc == 2)
    {
    ifstream f( argv[ 1 ] );
    if (!f)
      {
      cerr << "Could not open file " << argv[ 1 ] << endl;
      return 1;
      }

    return run( f );
    }

  return run( cin );
  }

Hope this helps.

[EvanEjk]

What does this line do?
int main( int argc, char** argv )
I'm guessing it puts the file name in argv. What does it put in argc?

What is this line sending to run()?
return run( cin );

[EvanEjk]

Okay, I am able to input a file, but now the output isn't working.
ofstream fileOut ("fileOut.txt");
It just isn't making "fileOut.txt".