std::replace() function with example in C++ STL

C++ STL | std::replace() function: Here, we are going to learn about the replace() function of algorithm header in C++ STL with example.
Submitted by IncludeHelp, on May 21, 2019

C++ STL std::replace() function

replace() function is a library function of algorithm header, it is used to replace an old value with a new value in the given range of a container, it accepts iterators pointing to the starting and ending positions, an old value to be replaced and a new value to be assigned.

Note: To use replace() function – include <algorithm> header or you can simple use <bits/stdc++.h> header file.

Syntax of std::replace() function

    std::replace(
        iterator start, 
        iterator end, 
        const T& old_value, 
        const T& new_value);

Parameter(s):

iterator start, iterator end – these are the iterators pointing to the starting and ending positions in the container, where we have to run the replace operation.
old_value – is the value to be searched and replaced with the new value.
new_value – a value to be assigned instead of an old_value.

Return value: void – it returns noting.

Example:

    Input:
    vector<int> v{ 10, 20, 10, 20, 10, 30, 40, 50, 60, 70 };
    
    //replacing 10 with 99
    replace(v.begin(), v.end(), 10, 99);
    
    Output:
    99 20 99 20 99 30 40 50 60 70

C++ STL program to demonstrate use of std::replace() function

In this program, we have a vector and we are assigning a new value to an old value.

//C++ STL program to demonstrate use of
//std::replace() function
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

int main()
{
    //vector
    vector<int> v{ 10, 20, 10, 20, 10, 30, 40, 50, 60, 70 };

    //printing vector elements
    cout << "before replacing, v: ";
    for (int x : v)
        cout << x << " ";
    cout << endl;

    //replacing 10 with 99
    replace(v.begin(), v.end(), 10, 99);

    //printing vector elements
    cout << "after replacing, v: ";
    for (int x : v)
        cout << x << " ";
    cout << endl;

    return 0;
}

Output

before replacing, v: 10 20 10 20 10 30 40 50 60 70
after replacing, v: 99 20 99 20 99 30 40 50 60 70

Reference: C++ std::replace()