std::for_each_n
From cppreference.com
| Defined in header <algorithm>
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| template< class InputIt, class Size, class UnaryFunction > InputIt for_each_n( InputIt first, Size n, UnaryFunction f ); |
(1) | (since C++17) |
| template< class ExecutionPolicy, class ForwardIt, class Size, class UnaryFunction2 > InputIt for_each_n( ExecutionPolicy&& policy, ForwardIt first, Size n, UnaryFunction2 f ); |
(2) | (since C++17) |
1) Applies the given function object
f to the result of dereferencing every iterator in the range [first, first + n), in order. 2) Applies the given function object
f to the result of dereferencing every iterator in the range [first, first + n) (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. If n is less than zero, the behavior is undefined.
Contents |
[edit] Parameters
| first | - | the beginning of the range to apply the function to |
| n | - | the number of elements 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, first + n) 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 | ||
-InputIt must meet the requirements of InputIterator.
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-ForwardIt must meet the requirements of ForwardIterator.
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-UnaryFunction must meet the requirements of MoveConstructible. Does not have to be CopyConstructible
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-UnaryFunction2 must meet the requirements of CopyConstructible.
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[edit] Return value
first + n
[edit] Complexity
Exactly n 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
ExecutionPolicyis one of the three standard policies, std::terminate is called. For any otherExecutionPolicy, the behavior is implementation-defined. - If the algorithm fails to allocate memory, std::bad_alloc is thrown.
[edit] Possible implementation
template<class InputIt, class Size, class UnaryFunction> InputIt for_each_n(InputIt first, Size n, UnaryFunction f) { for (Size i = 0; i < n; ++first, (void) ++i) { f(*first); } return first; } |
[edit] Example
| This section is incomplete Reason: no example |
[edit] See also
| applies a function to a range of elements (function template) | |
| range-for loop | executes loop over range (since C++11) |
| applies a function to a range of elements (function template) |