std::for_each

Header: <algorithm>

Applies the given function object f to the result of dereferencing every iterator in the range [first,last). If f returns a result, the result is ignored.

# Declarations

template< class InputIt, class UnaryFunc >
UnaryFunc for_each( InputIt first, InputIt last, UnaryFunc f );

(constexpr since C++20)

template< class ExecutionPolicy, class ForwardIt, class UnaryFunc >
void for_each( ExecutionPolicy&& policy,
ForwardIt first, ForwardIt last, UnaryFunc f );

(since C++17)

# Parameters

• first, last: the range to apply the function to
• policy: the execution policy to use
• f: function object, to be applied to the result of dereferencing every iterator in the range [first, last) The signature of the function should be equivalent to the following: void fun(const Type &a); The signature does not need to have const &. The type Type must be such that an object of type InputIt can be dereferenced and then implicitly converted to Type.

# Notes

For overload (1), f can be a stateful function object. The return value can be considered as the final state of the batch operation.

For overload (2), multiple copies of f may be created to perform parallel invocation. No value is returned because parallelization often does not permit efficient state accumulation.

# Example

#include <algorithm>
#include <iostream>
#include <vector>
 
int main()
{
    std::vector<int> v{3, -4, 2, -8, 15, 267};
 
    auto print = [](const int& n) { std::cout << n << ' '; };
 
    std::cout << "before:\t";
    std::for_each(v.cbegin(), v.cend(), print);
    std::cout << '\n';
 
    // increment elements in-place
    std::for_each(v.begin(), v.end(), [](int &n) { n++; });
 
    std::cout << "after:\t";
    std::for_each(v.cbegin(), v.cend(), print);
    std::cout << '\n';
 
    struct Sum
    {
        void operator()(int n) { sum += n; }
        int sum {0};
    };
 
    // invoke Sum::operator() for each element
    Sum s = std::for_each(v.cbegin(), v.cend(), Sum());    
    std::cout << "sum:\t" << s.sum << '\n';
}

# Defect reports

# See also

• transform
• for_each_n
• ranges::for_each
• ranges::for_each_n
• range-for loop