std::for_each

std::for_each

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Prerequisites

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1. What is std::for_each?

std::for_each is an algorithm that applies a function to each element in a range.

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

int main()
{
    std::vector<int> v = {1, 2, 3, 4, 5};

    std::for_each(v.begin(), v.end(), [](int x)
    {
        std::cout << x << " ";
    });
}

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2. Example

2-1. Lambda

std::for_each(v.begin(), v.end(), [](int& x)
{
    x *= 2;
});

2-2. Function Pointer

void print(int x)
{
    std::cout << x << " ";
}

std::for_each(v.begin(), v.end(), print);

2-3. Functor

struct Multiply
{
    void operator()(int& x)
    {
        x *= 2;
    }
};

std::for_each(v.begin(), v.end(), Multiply());

2-4. Return Value

auto f = std::for_each(...);

Returns the function object used

struct Counter
{
    int count = 0;

    void operator()(int)
    {
        count++;
    }
};

Counter c = std::for_each(v.begin(), v.end(), Counter());
std::cout << c.count;

2-5. Parallel Execution(C++17)

#include <execution>

std::for_each(std::execution::par, v.begin(), v.end(), [](int& x)
{
    x *= 2;
});

Parallel for_each requires thread-safe operations