std:: for_each

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.

If the iterator type ( InputIt / ForwardIt ) is mutable, f may modify the elements of the range through the dereferenced iterator.

Unlike the rest of the parallel algorithms, for_each is not allowed to make copies of the elements in the sequence even if they are TriviallyCopyable .

Parameters

Return value

Complexity

Exactly std:: distance ( first, last ) applications of f .

Exceptions

The overload with a template parameter named ExecutionPolicy reports errors as follows:

• If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies , std::terminate is called. For any other ExecutionPolicy , the behavior is implementation-defined.
• If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation

See also the implementations in libstdc++ , libc++ and MSVC stdlib .

template<class InputIt, class UnaryFunc>
constexpr UnaryFunc for_each(InputIt first, InputIt last, UnaryFunc f)
{
    for (; first != last; ++first)
        f(*first);
 
    return f; // implicit move since C++11
}

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';
}

before:	3 -4 2 -8 15 267 
after:	4 -3 3 -7 16 268 
sum:	281

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also