Avoid appending first line when writing to a text file

Question

I have a program that takes user input and writes it to a text file. However, when I try to append to my text file, it rewrites my "header" line. How can I avoid that?

// StudyTime.cpp : 
/* Track study time
accept user input
store in .txt file
*/

#include "stdafx.h"
#include <string>
#include <iostream>
#include <fstream>
#include <iomanip>

using namespace std;

int main()
{
    string date = "";
    double hours = 0;
    const string filename = "StudyTime.txt";

    ofstream myfile (filename, ios_base::app); //create filename and allow appending

    myfile << "Date" << setw(15) << "Study Time" << endl; //Header line

    //prompt user for Date
    cout << "Date: "; 
    cin >> date;

    //prompt user for hours
    cout << "Hours: ";
    cin >> hours;

    if (date.size() == 3) {
        myfile << date << setw(8) << hours << endl; //write date and hours to txt file
    }

    else if (date.size() == 4) {
        myfile << date << setw(7) << hours << endl; //write date and hours to txt file
    }

    else
        myfile << date << setw(6) << hours << endl; //write date and hours to txt file

    myfile.close(); //close file

    return 0;
}

Check if the file exists, then check the size, if it's zero write a header? — atomSmasher, Jan 28 '18 at 03:06

Sean F · Answer 1 · 2018-01-28T03:29:02.790

You're running this more than once.

Each time you run, you open with ios_base::app

That means the result is appending to the previous file contents.

To rewrite the file each time, use ios_base::trunc

ofstream myfile (filename, ios_base::trunc);

Also, you might as well just write one line instead of the if/else if/else:

myfile << date << setw(11 - date.size()) << hours << endl; //write date and hours to txt file

If you want to append and you need to decide whether to write the header or not, check if the file exists: Fastest way to check if a file exist using standard C++/C++11/C?

For instance:

 ifstream f(filename);
 bool exists = f.good();
 f.close();

score 0 · Accepted Answer · answered Jan 28 '18 at 03:39

Before adding a header, you can check the file to see if it already has a header. The code below should work. I added a function hasHeader that checks to see if the header already exists in the file, and if so, returns true. In such case, the header is not appended.

#include "stdafx.h"
#include <string>
#include <iostream>
#include <fstream>
#include <iomanip>

using namespace std;

bool fileHasHeader(string file)
{
  char line[100];
  ifstream myfile;
  myfile.open(file, ifstream::in);
  myfile.getline(line, 100);
  bool hasHeader = false;
  if (strcmp(line, "Date     Study Time") == 0) {
    hasHeader = true;
  }
  myfile.close();

  return hasHeader;
}

int main()
{
  string date = "";
  double hours = 0;
  const string filename = "StudyTime.txt";

  ofstream myfile (filename, ios_base::app); //create filename and allow appending

  if (!fileHasHeader(filename)) {
    myfile << "Date" << setw(15) << "Study Time" << endl; //Header line
  }

  //prompt user for Date
  cout << "Date: "; 
  cin >> date;

  //prompt user for hours
  cout << "Hours: ";
  cin >> hours;

  if (date.size() == 3) {
    myfile << date << setw(8) << hours << endl; //write date and hours to txt file
  }

  else if (date.size() == 4) {
    myfile << date << setw(7) << hours << endl; //write date and hours to txt file
  }

  else
    myfile << date << setw(6) << hours << endl; //write date and hours to txt file

  myfile.close(); //close file

  return 0;
}

Avoid appending first line when writing to a text file

2 Answers2