std::for_each

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Algorithm library

Functions
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each countcount_if mismatch equal	findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n removeremove_if remove_copyremove_copy_if	replacereplace_if replace_copyreplace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffleshuffle (until C++17)(C++11) unique unique_copy
Partitioning operations
is_partitioned (C++11) partition partition_copy (C++11)	stable_partition partition_point (C++11)
Sorting operations (on sorted ranges)
is_sorted (C++11) is_sorted_until (C++11) sort	partial_sort partial_sort_copy stable_sort nth_element
Binary search operations (on sorted ranges)
lower_bound upper_bound	binary_search equal_range
Set operations (on sorted ranges)
merge inplace_merge includes	set_difference set_intersection set_symmetric_difference set_union
Heap operations
is_heap (C++11) is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
Minimum/maximum operations
max max_element min min_element minmax (C++11) minmax_element (C++11)	lexicographical_compare is_permutation (C++11) next_permutation prev_permutation
Numeric operations
iota (C++11) accumulate inner_product	adjacent_difference partial_sum
C library
qsort	bsearch

 

Defined in header <algorithm>
template< class InputIt, class UnaryFunction > UnaryFunction for_each( InputIt first, InputIt last, UnaryFunction f );

Applies the given function object f to the result of dereferencing every iterator in the range [first, last), in order.

If InputIt is a mutable iterator, f may modify the elements of the range through the dereferenced iterator. If f returns a result, the result is ignored.

Parameters

first, last	-	the range to apply the function to
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.
- UnaryFunction must meet the requirements of MoveConstructible. Does not have to be CopyConstructible

Return value

f	(until C++11)
std::move(f)	(since C++11)

Complexity

Exactly last - first applications of f

Possible implementation

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

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:

Run this code

#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, 9, 15, 267};
 
    std::cout << "before:";
    for (auto n : nums) {
        std::cout << ' ' << n;
    }
    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: ";
    for (auto n : nums) {
        std::cout << ' ' << n;
    }
    std::cout << '\n';
    std::cout << "sum: " << s.sum << '\n';
}

Output:

before: 3 4 2 9 15 267
after:  4 5 3 10 16 268
sum: 306

See also

transform	applies a function to a range of elements (function template)
range-for loop	executes loop over range (since C++11)
for_each (parallelism TS)	similar to std::for_each except returns void (function template)
for_each_n (parallelism TS)	applies a function object to the first n elements of a sequence (function template)