Editing a file in C++ : help me

I want to edit a text file using c++.
Suppose the content of the file is:

I am a boy.
I am 20 years old.
I live in India.

Now I want to make it:

I am a boy.
I am 22 years old.
I live in India.

I want to change it this way. Find a particular word and replace it. Is it possible to do it this way rather than replacing the whole file by duplicating the the unchanged content.
Please help me.

 

I found this code ages ago, and it's worked nicely for me.

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

int main()
{
    string originalText = "This is a test string";
    string search = "test";
    string replace = "new";

    string buffer = "";
    stringstream replaced("");
    stringstream original(originalText);

    while (original >> buffer)
    {
        if (buffer == search) replaced << replace << " ";
        else replaced << buffer << " ";
    }
    cout << replaced.str();

    return 0;
}

Code (markup):

 

I dont think you code edits a text file.

 

You do know how to read and write a text file right?
By using above algorithm, it can be done.

1- Read the text file
2- Find the word (by using string) that you want to change
3- Replace the string

Done