< cpp‎ | algorithm
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
Sampling operations

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Lexicographical comparison operations
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
Defined in header <algorithm>
template< class InputIt, class UnaryFunc >
UnaryFunc for_each( InputIt first, InputIt last, UnaryFunc f );
(1) (constexpr since C++20)
template< class ExecutionPolicy, class ForwardIt, class UnaryFunc >

void for_each( ExecutionPolicy&& policy,

               ForwardIt first, ForwardIt last, UnaryFunc f );
(2) (since C++17)

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

1) f is applied in order starting from first.

If UnaryFunc is not MoveConstructible, the behavior is undefined.

(since C++11)
2) f might not be applied in order. The algorithm is executed according to policy.
This overload participates in overload resolution only if

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.

(until C++20)

std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.

(since C++20)
If UnaryFunc is not CopyConstructible, the behavior is undefined.

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.


[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 [firstlast)

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 LegacyInputIterator.
ForwardIt must meet the requirements of LegacyForwardIterator.

[edit] Return value

1) f
2) (none)

[edit] Complexity

Exactly std::distance(first, last) 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 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

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)
    return f; // implicit move since C++11

[edit] 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.

[edit] Example

The following example uses a lambda-expression to increment all of the elements of a vector and then uses an overloaded operator() in a function object (a.k.a., "functor") to compute their sum. Note that to compute the sum, it is recommended to use the dedicated algorithm std::accumulate.

#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

[edit] Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 475 C++98 it was unclear whether f can modify the elements
of the sequence being iterated over (for_each is
classified as “non-modifying sequence operations”)
made clear (allowed if the
iterator type is mutable)
LWG 2747 C++11 overload (1) returned std::move(f) returns f (which implicitly moves)

[edit] See also

applies a function to a range of elements, storing results in a destination range
(function template) [edit]
applies a function object to the first N elements of a sequence
(function template) [edit]
applies a function to a range of elements
applies a function object to the first N elements of a sequence
range-for loop(C++11) executes loop over range[edit]