How to preserve old data in the file when adding new data

Question

How do I add new data to the file without destroying the old data? The data contains name and age fields. Here is my code:

#include <fstream>
#include <iostream>
#include <string>

using namespace std;

int main() {
    char data[100];
    ofstream outfile;
    outfile.open("afile.txt");
    cout << "Writing to the file" << endl;
    cout << "Enter your name: "; 
    cin.getline(data, 100);
    outfile << data << endl;
    cout << "Enter your age: "; 
    cin >> data;
    cin.ignore();
    outfile << data << endl;
    outfile.close();

    ifstream infile; 
    infile.open("afile.txt"); 
    cout << "Reading from the file" << endl; 
    infile >> data; 
    cout << data << endl;
    infile >> data; 
    cout << data << endl; 
    infile.close();
    return 0;
}

Answer 1

According to std::ofstream

void open (const string& filename, ios_base::openmode mode = ios_base::out);

where std::ios_base::openmode is one of the following

• app (append) Set the stream's position indicator to the end of the stream before each output operation.
• ate (at end) Set the stream's position indicator to the end of the stream on opening.
• binary (binary) Consider stream as binary rather than text.
• in (input) Allow input operations on the stream.
• out (output) Allow output operations on the stream.
• trunc (truncate) Any current content is discarded, assuming a length of zero on opening.

You can combine openmodes with |

std::ios_base::openmode::out | std::ios_base::openmode::app

This will open file for writing, appending data to the end.