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C++ Program to Append Data in a File



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

What to Do before Program ?

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

c++ program append data in file

As you can see from above snapshot, the file named codescracker.txt is available. That is created by me, right now. Let's put some content inside it. Here is the snapshot of the opened file, after writing some data manually, inside the file:

append data in file c++

Since I've 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 user at run-time to this file, using a C++ program.

Append Data in a File

The question is, write a program in C++ that receives the name of file and data, to append 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 above C++ program on appending data in a file:

append data in file program c++

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

The first
text gets
append

That is, first type The first, then press ENTER key, again type text to and again press ENTER key, 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 like shown in the snapshot given below. Here is its sample run with exactly same inputs:

c++ append data in file program

Now if you see the same file, codescracker.txt, then you'll found that the above entered texts/data gets appended. Here is the new snapshot of the opened file:

c++ program append content in file

Note - The fstream header file is included to use its class fstream, to handle with file stream.

Note - The fstream is a stream class used for both read and write purpose.

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

But the above program does not provides a good user experience. I mean, user doesn't see the on-going process of above program. Even they are not able to see, whether the data entered by him/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 name of file, and:

The second
text to
append.

as data to append, and y as choice:

c++ program append text in file

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

c++ program appending data in file

As you can see from the above program and its sample run, user is able to see the on-going process as well as the content of file (if he/she wants) after appending new data in the file. That is, basically user need not 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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