How to use the replace_copy() function in C++

Overview

In this shot, we will learn how to use the replace_copy() function in C++. This function is available in the <algorithm> library in C++.

The replace_copy() function replaces each element in the range [first, last) that is equal to oldValue with newValue and creates a copy. The function uses the operator ==, meaning double equal to, to compare each of the elements to old_value.

Parameter

The replace_copy() method takes the following parameters:

First: Forward iterator for the initial position of the derived range.
Last: Forward iterator for the final position of the derived range.
Result: Forward iterator for the initial position of the range where the final result is stored.
Old value: Replaced value.
New value: Replacement value.

Return

The replace_copy() function returns the iterator after the last copied element in the destination range.

Syntax

The syntax of the replace_copy() function is shown below:

Iterator replace_copy(first, last, result, oldvalue, newvalue);

#include <iostream>
#include <algorithm>
#include <vector>
#include <iterator>
using namespace std;
bool isEVEN(int x)
{
    if (x % 2 == 0)
        return 1;
    else
        return 0;
}
int main()
{
    vector<int> vec = { 33,21,24,21,21 };
    vector<int> result(vec.size());  
    cout<<"Vector before replace_copy() implementation: ";
    for (int x : vec)
        cout << x << " ";
    cout << endl;
    replace_copy(vec.begin(), vec.end(), result.begin(), 21, 2000);  
    
    cout<<"Vector after replace_copy() implementation: ";
    
    for (int x : result)
        cout << x << " ";
    cout<<endl;
    
 return 0;
}

Explanation

In lines 1 to 3, we import the required header files.
In lines 8 to 14, we define a function which checks whether a number is even.
In line 16, we make a main function.
In line 18, we declare a vector of the int type.
In line 19, we declare our result vector where the copied range will be stored.
In line 20, we display the message regarding the original vector.
In line 21 to 22, we display the original vector.
In line 25, we use the replace_copy() function to replace all the value = 21 with value = 2000 and display the transformed vector.
In line 29 to 30, we display the result vector.

This is how we can use the replace_copy() function in C++.