C++ Program to Append Data in a File

This article is created to provide you with the program in C++ that appends some data to a file. Here, both data and files must be entered by the user at run-time. Adding new data to a file without erasing the previous one is referred to as appending data.

What Should You Do Before the Program?

A file is required to append some data inside the file. Therefore, I've created a file inside the current directory (the folder where my C++ source code is saved or going to be saved). Here is the snapshot of the current directory where the file was created:

The file named codescracker.txt is available, as shown in the above screenshot.That is created by me right now. Let's put some content inside it. Here is a snapshot of the opened file after writing some data manually inside it:

since I've got a file with some data already available in it. Therefore, now let's move on and create a program in C++ that appends some new data entered by the user at run-time to this file using a C++ program.

Append Data in a File

The question is: write a C++ program that receives the name of a file and data and appends the given data inside the given file. The answer to this question is the program given below:

#include<iostream>
#include<fstream>
#include<string.h>

using namespace std;
int main()
{
   char filename[20], str[500];
   fstream fp;
   cout<<"Enter File's Name: ";
   gets(filename);
   fp.open(filename, fstream::app);
   if(!fp)
   {
      cout<<"\nFile doesn't exist or Access denied!";
      return 0;
   }
   cout<<"Enter the Data: ";
   gets(str);
   while(strlen(str)>0)
   {
      fp<<"\n";
      fp<<str;
      gets(str);
   }
   fp.close();
   cout<<endl;
   return 0;
}

The snapshot given below shows the initial output produced by the above C++ program on appending data to a file:

Now provide the name of the file that was created earlier, which is codescracker.txt, and then enter some data, saying:

The first
text gets
append

That is, type The first, then press the ENTER key, then type text to and press the ENTER key again, and finally type append and hit the ENTER key two times to stop entering further data and append the complete data entered in the file codescracker.txt, as shown in the snapshot given below. Here is its sample run with exactly the same inputs:

Now if you see the same file, codescracker.txt, then you'll find that the above-entered texts and data get appended. Here is the new snapshot of the opened file:

Note: The fstream header file is included to use its class fstream to handle the file stream.

Note: The fstream is a stream class used for both read and write purposes.

Note: The fstream::app is used to open the file in appending mode.

But the above program does not provide a good user experience. I mean, the user doesn't see the on-going process of the above program. Even they are not able to see whether the data entered by him or her gets appended or not. Therefore, I've created another program that gives a good user experience:

#include<iostream>
#include<fstream>
#include<string.h>

using namespace std;
int main()
{
   char filename[20], str[500], ch;
   fstream fp;
   cout<<"Enter File's Name: ";
   gets(filename);
   fp.open(filename, fstream::app);
   if(!fp)
   {
      cout<<"\nFile doesn't exist or Access denied!";
      return 0;
   }
   else
      cout<<"\nThe file is available in the directory";
   cout<<"\nEnter the Data: ";
   gets(str);
   while(strlen(str)>0)
   {
      fp<<"\n";
      fp<<str;
      gets(str);
   }
   cout<<"\nEntered data appended to the file successfully!";
   fp.close();
   cout<<"\nWant to see the content of file ? (y/n) ";
   cin>>ch;
   if(ch=='y')
   {
      fstream fp;
      fp.open(filename, fstream::in);
      cout<<"-----"<<filename<<"--------\n";
      while(fp>>noskipws>>ch)
         cout<<ch;
      fp.close();
   }
   cout<<endl;
   return 0;
}

Here is its sample run with user inputs, codescracker.txt as the name of the file, and:

The second
text to
append.

as data to append, and y as a choice:

And here is the new snapshot of the opened file, codescracker.txt:

As you can see from the above program and its sample run, the user is able to see the on-going process as well as the content of the file (if he or she wants) after appending new data to the file. That is, basically, the user does not need to go inside the directory and open the file manually to see its new content after appending, as this is done using the program itself.

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