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std::fill_n

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< cpp‎ | algorithm
 
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fill_n
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Defined in header <algorithm>
(1)
template< class OutputIt, class Size, class T >
OutputIt fill_n( OutputIt first, Size count, const T& value );
 (constexpr since C++20)
(until C++26)
template< class OutputIt, class Size,

          class T = typename std::iterator_traits
                        <OutputIt>::value_type >
constexpr OutputIt fill_n( OutputIt first, Size count,

                           const T& value );
 (since C++26)
(2)
template< class ExecutionPolicy,

          class ForwardIt, class Size, class T >
ForwardIt fill_n( ExecutionPolicy&& policy,

                  ForwardIt first, Size count, const T& value );
 (since C++17)
(until C++26)
template< class ExecutionPolicy,

          class ForwardIt, class Size,
          class T = typename std::iterator_traits
                        <OutputIt>::value_type >
ForwardIt fill_n( ExecutionPolicy&& policy,

                  ForwardIt first, Size count, const T& value );
 (since C++26)
1) Assigns the given value to the first count elements in the range beginning at first if count > 0. Does nothing otherwise.
2) Same as (1), but executed according to policy.
This overload participates in overload resolution only if all following conditions are satisfied:

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 any of the following conditions is satisfied, the program is ill-formed:

Contents

[edit] Parameters

first - the beginning of the range of elements to modify
count - number of elements to modify
value - the value to be assigned
policy - the execution policy to use
Type requirements
-
OutputIt must meet the requirements of LegacyOutputIterator.
-
ForwardIt must meet the requirements of LegacyForwardIterator.

[edit] Return value

Iterator one past the last element assigned if count > 0, first otherwise.

[edit] Complexity

Exactly std::max(0, count) assignments.

[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.

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