< cpp‎ | algorithm
Algorithm library
Execution policies (C++17)
Non-modifying sequence operations
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations

Numeric operations
C library
Defined in header <algorithm>
template< class InputIt, class UnaryFunction >
UnaryFunction for_each( InputIt first, InputIt last, UnaryFunction f );
template< class ExecutionPolicy, class ForwardIt, class UnaryFunction2 >
void for_each( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, UnaryFunction2 f );
(2) (since C++17)
1) Applies the given function object f to the result of dereferencing every iterator in the range [first, last), in order.
2) Applies the given function object 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.


[edit] Parameters

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:

 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.

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.

[edit] Return value

1) f (until C++11) std::move(f) (since C++11)
2) (nothing)

[edit] Complexity

Exactly last - first applications of f

[edit] 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 three 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.

[edit] Possible implementation

template<class InputIt, class UnaryFunction>
UnaryFunction for_each(InputIt first, InputIt last, UnaryFunction f)
    for (; first != last; ++first) {
    return f;

[edit] Example

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';


before: 3 4 2 8 15 267
after:  4 5 3 9 16 268
sum: 305

[edit] See also

applies a function to a range of elements
(function template) [edit]
range-for loop executes loop over range (since C++11) [edit]
applies a function object to the first n elements of a sequence
(function template) [edit]