C++ program to append content of one text file to another

Last Updated : 23 Nov, 2022

Given source and destination text files. Append the content from the source file to the destination file and then display the content of the destination file.
Example :

Input : file.txt : "geeks", file2.txt : "geeks for"
Output: file2.txt : "geeks for geeks"

Method 1:
Approach:

Open file.txt in inputstream and file2.txt in outputstream with the append option, so that the previous content of the file are not deleted.
Check if there’s an error in opening or locating a file. If yes, then throw an error message.
If both files are found, then write content from the source file to the destination file.
Display the content of the destination file.

Below is the implementation of the above approach:

CPP

// C++ implementation to append 
// content from source file to 
// destination file 
#include <bits/stdc++.h> 
using namespace std; 

// driver code 
int main() 
{ 
    fstream file; 

    // Input stream class to 
    // operate on files. 
    ifstream ifile("file.txt", ios::in); 

    // Output stream class to 
    // operate on files. 
    ofstream ofile("file2.txt", ios::out | ios::app); 

    // check if file exists 
    if (!ifile.is_open()) { 

        // file not found (i.e, not opened). 
        // Print an error message. 
        cout << "file not found"; 
    } 
    else { 
        // then add more lines to 
        // the file if need be 
        ofile << ifile.rdbuf(); 
    } 
    string word; 

    // opening file 
    file.open("file2.txt"); 

    // extracting words form the file 
    while (file >> word) { 

        // displaying content of 
        // destination file 
        cout << word << " "; 
    } 

    return 0; 
}

Output

file not found

Method 2: We can do the same using different functions mentioned below:

fopen(): Returns a pointer to the object that controls the opened file stream
fprintf(): Writes the string pointed by format to the stream
fclose(): Closes the file associated with the stream and disassociates it.
fgetc(): Returns the character currently pointed by the internal file position indicator of the specified stream

Approach:

Open source file in read mode and destination file in append mode using fopen()
check if they exist
Iterate every character of the source file using fgetc() and print it to the destination file using fprintf() with while loop
Close both files using fclose()
Open destination file in read mode
print it
close it

Below is the implementation of the above approach:

C++

// C++ program to Append and Read text of text files
#include <bits/stdc++.h>

using namespace std;
int main()
{
    // open file in read mode to read it's content
    FILE* file = fopen("file.txt", "r");
  
    // open file in append mode to append read content
    FILE* file2 = fopen("file2.txt", "a");
    if (file2 == NULL) {
        cout << "file not found";
        return 1;
    }
    else if (file == NULL) {
        cout << "file not found";
        return 1;
    }
  
    // Read contents from file
    char ch = fgetc(file);
    while (ch != EOF) {
      
        // print read content from file in file2
        fprintf(file2, "%c", ch);
        ch = fgetc(file);
    }
    fclose(file);
    fclose(file2);
  
    // open file 2 again in read mode to read the content
    FILE* file3 = fopen("file2.txt", "r");
  
    // Read contents from file
    char ch2 = fgetc(file3);
    while (ch2 != EOF) {
      
        // print read content from file
        printf("%c", ch2);
        ch2 = fgetc(file3);
    }
    fclose(file3);
}

// This code is contributed by Shivesh Kumar Dwivedi