std::for_each
From cppreference.com
Defined in header
<algorithm>
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template< class InputIt, class UnaryFunction >
UnaryFunction for_each( InputIt first, InputIt last, UnaryFunction f ); |
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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.
Contents |
[edit] 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 &. |
Type requirements | ||
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InputIt must meet the requirements of InputIterator .
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UnaryFunction must meet the requirements of MoveConstructible . Does not have to be CopyConstructible
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[edit] Return value
f |
(until C++11) |
std::move(f) | (since C++11) |
[edit] Complexity
Exactly last
- first
applications of f
[edit] Possible implementation
template<class InputIt, class UnaryFunction> UnaryFunction for_each(InputIt first, InputIt last, UnaryFunction f) { for (; first != last; ++first) { f(*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:
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
[edit] See also
applies a function to a range of elements (function template) |
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range-for loop | executes loop over range (since C++11) |
(parallelism TS)
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similar to std::for_each except returns void (function template) |
(parallelism TS)
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applies a function object to the first n elements of a sequence (function template) |