Defined in header <algorithm>  

template< class InputIt, class UnaryFunction > UnaryFunction for_each( InputIt first, InputIt last, UnaryFunction f );  (1)  
template< class ExecutionPolicy, class ForwardIt, class UnaryFunction2 > void for_each( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, UnaryFunction2 f );  (2)  (since C++17) 
f
to the result of dereferencing every iterator in the range [first, last)
, in order. f
to the result of dereferencing every iterator in the range [first, last)
(not necessarily in order). The algorithm is executed according to policy
. This overload does not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
is true.For both overloads, if the iterator type is mutable, f
may modify the elements of the range through the dereferenced iterator. If f
returns a result, the result is ignored.
Unlike the rest of the algorithms, for_each is not allowed to make copies of the elements in the sequence even if they are trivially copyable.
first, last    the range to apply the function to 
policy    the execution policy to use. See execution policy for details. 
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:
The signature does not need to have 
Type requirements  
InputIt must meet the requirements of InputIterator . 

ForwardIt must meet the requirements of ForwardIterator . 

UnaryFunction must meet the requirements of MoveConstructible . Does not have to be CopyConstructible 

UnaryFunction2 must meet the requirements of CopyConstructible . 
f
(until C++11) std::move(f)
(since C++11)
Exactly last
 first
applications of f
.
The overload with a template parameter named ExecutionPolicy
reports errors as follows:
ExecutionPolicy
is one of the three standard policies, std::terminate
is called. For any other ExecutionPolicy
, the behavior is implementationdefined. std::bad_alloc
is thrown. template<class InputIt, class UnaryFunction> UnaryFunction for_each(InputIt first, InputIt last, UnaryFunction f) { for (; first != last; ++first) { f(*first); } return f; } 
The following example uses a lambda function to increment all of the elements of a vector and then uses an overloaded operator()
in a functor to compute their sum:
#include <vector> #include <algorithm> #include <iostream> struct Sum { Sum(): sum{0} { } void operator()(int n) { sum += n; } int sum; }; int main() { std::vector<int> nums{3, 4, 2, 8, 15, 267}; auto print = [](const int& n) { std::cout << " " << n; }; std::cout << "before:"; std::for_each(nums.begin(), nums.end(), print); std::cout << '\n'; std::for_each(nums.begin(), nums.end(), [](int &n){ n++; }); // calls Sum::operator() for each number Sum s = std::for_each(nums.begin(), nums.end(), Sum()); std::cout << "after: "; std::for_each(nums.begin(), nums.end(), print); std::cout << '\n'; std::cout << "sum: " << s.sum << '\n'; }
Output:
before: 3 4 2 8 15 267 after: 4 5 3 9 16 268 sum: 305
applies a function to a range of elements (function template) 

rangefor loop  executes loop over range (since C++11) 
(C++17)  applies a function object to the first n elements of a sequence (function template) 
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