Thread: Output File Help please

You probably don't want to open the file in append mode. The easiest thing to do in most of these cases is to open the file in read mode, then read the entire contents of the file into your container (array or whatever) at the beginning of the program and then close the file. Operate upon this container within the 'guts" of your program, adds/deletes/etc... At the end of your program, you open the same file but this time in write mode and you simply write the entire contents of the container back to the file completely overwritting what was previously in the file. You cannot just delete something from the middle of a file and just expect everything around that position to shift around for you.

>>so is there a way I can remove it?
Not easily. Unless the system supports a very specialized record-oriented file type, you have no choice but to remove from a file as you would from an array: Shift everything from the deleted item backward to fill the hole created by a deletion. A simple implementation would use a helper data structure:

Code:

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

using namespace std;

bool show_file(const char *name)
{
  ifstream fin(name);
  string s;

  if (!fin)
    return false;

  while (getline(fin, s))
    cout<< s <<endl;

  return true;
}

int main()
{ 
  cout<<"Before:\n";
  if (!show_file("test.txt")) {
    cerr<<"Error processing file"<<endl;
    return EXIT_FAILURE;
  }

  string s;
  vector<string> mem_file;
  ifstream fin("test.txt");

  if (!fin) {
    cerr<<"Error opening file"<<endl;
    return EXIT_FAILURE;
  }

  while (getline(fin, s))
    mem_file.push_back(s);

  if (!fin.eof()) {
    cerr<<"Error processing file"<<endl;
    return EXIT_FAILURE;
  }

  ofstream fout("test.txt");

  if (!fout) {
    cerr<<"Error opening file"<<endl;
    return EXIT_FAILURE;
  }

  // Remove the second line
  for (vector<string>::size_type i = 0; i < mem_file.size(); i++)
  {
    if (i != 1)
      fout<< mem_file[i] <<endl;
  }

  cout<<"After:\n";
  if (!show_file("test.txt")) {
    cerr<<"Error processing file"<<endl;
    return EXIT_FAILURE;
  }

  return EXIT_SUCCESS;
}