for_each loop in C++

What is std::for_each?

abstract

• A function for applying a function to elements in the given iterator range.
• This makes it possible to do things like display all element in a vector without using a for statement.
• References：for_each - cpprefjp C++日本語リファレンス

Ex.1：Display all elements of a vector

• The argument which is used in this case shown below.

1st	Iterator to the beginning of the input
2nd	Iterator to the end of the input
3rd	lambda expressions or function

When using lambda expressions

If v1 is input and v2 is input, the arguments should be as follows:

1st	v1.begin()
2nd	v1.end()
3rd	[](int x) { std::cout << x << std::endl; }

Source Code

#include <algorithm>
#include <iostream>
#include <vector>

int main() {
    std::vector<int> v1{3, 5, 6, 7, 8};

    // use for_each loop
    std::for_each(
        v1.begin(), 
        v1.end(), 
        [](int x) { std::cout << x << std::endl; }
    );
}

Result

3
5
6
7
8

When using a function

• Change the 3rd argument。

Source Code(The result is the same)

#include <algorithm>
#include <iostream>
#include <vector>

// The function displaying the argument.
void display(int n){
    std::cout << n << std::endl;
}

int main() {
    std::vector<int> v1{3, 5, 6, 7, 8};

    // use for_each loop
    std::for_each(
        v1.begin(), 
        v1.end(), 
        display
    );
}