std::uninitialized_fill (3) - Linux Manuals

std::uninitialized_fill: std::uninitialized_fill

NAME

std::uninitialized_fill - std::uninitialized_fill

Synopsis

Defined in header <memory>
template< class ForwardIt, class T > (1)
void uninitialized_fill( ForwardIt first, ForwardIt last, const T& value );
template< class ExecutionPolicy, class ForwardIt, class T > (2) (since C++17)
void uninitialized_fill( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, const T& value );

1) Copies the given value to an uninitialized memory area, defined by the range [first, last) as if by

  for (; first != last; ++first)
    ::new (static_cast<void*>(std::addressof(*first)))
        typename std::iterator_traits<ForwardIt>::value_type(value);

If an exception is thrown during the initialization, the objects already constructed are destroyed in an unspecified order.
2) Same as (1), but executed according to policy. This overload does not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

Parameters

first, last - the range of the elements to initialize
value - the value to construct the elements with
policy - the execution policy to use. See execution_policy for details.

Type requirements

-
ForwardIt must meet the requirements of LegacyForwardIterator.
-
No increment, assignment, comparison, or indirection through valid instances of ForwardIt may throw exceptions.

Return value

(none)

Complexity

Linear in the distance between first and last

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.

Possible implementation

  template<class ForwardIt, class T>
  void uninitialized_fill(ForwardIt first, ForwardIt last, const T& value)
  {
      typedef typename std::iterator_traits<ForwardIt>::value_type Value;
      ForwardIt current = first;
      try {
          for (; current != last; ++current) {
              ::new (static_cast<void*>(std::addressof(*current))) Value(value);
          }
      } catch (...) {
          for (; first != current; ++first) {
              first->~Value();
          }
          throw;
      }
  }

Example

// Run this code

  #include <algorithm>
  #include <iostream>
  #include <memory>
  #include <string>
  #include <tuple>

  int main()
  {
      std::string* p;
      std::size_t sz;
      std::tie(p, sz) = std::get_temporary_buffer<std::string>(4);

      std::uninitialized_fill(p, p+sz, "Example");

      for (std::string* i = p; i != p+sz; ++i) {
          std::cout << *i << '\n';
          i->~basic_string<char>();
      }
      std::return_temporary_buffer(p);
  }

Output:

Example

Example

Example

Example