std::uninitialized_fill_n
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | Defined in header  <memory> | ||
| (1) | ||
| template< class ForwardIt, class Size, class T > void uninitialized_fill_n( ForwardIt first, Size count, const T& value ); | (until C++11) | |
| template< class ForwardIt, class Size, class T > ForwardIt uninitialized_fill_n( ForwardIt first, Size count, const T& value ); | (since C++11) | |
| template< class ExecutionPolicy, class ForwardIt, class Size, class T > ForwardIt uninitialized_fill_n( ExecutionPolicy&& policy, ForwardIt first, Size count, const T& value ); | (2) | (since C++17) | 
1) Copies the given value 
value to the first count elements in an uninitialized memory area beginning at first as if by
for (; n--; ++first) ::new (static_cast<void*>(std::addressof(*first))) typename std::iterator_traits<ForwardIt>::value_type(x);
 If an exception is thrown during the initialization, the function has no effects. 
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| Contents | 
[edit] Parameters
| first | - | the beginning of the range of the elements to initialize | 
| count | - | number of elements to construct | 
| value | - | the value to construct the elements with | 
| Type requirements | ||
| - ForwardItmust meet the requirements ofForwardIterator. | ||
| -No increment, assignment, comparison, or indirection through valid instances of ForwardItmay throw exceptions. | ||
[edit] Return value
| (none) | (until C++11) | 
| Iterator to the element past the last element copied. | (since C++11) | 
[edit] Complexity
Linear in count.
[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 ForwardIt, class Size, class T > ForwardIt uninitialized_fill_n(ForwardIt first, Size count, const T& value) { typedef typename std::iterator_traits<ForwardIt>::value_type Value; ForwardIt current = first; try { for (; count > 0; ++current, (void) --count) { ::new (static_cast<void*>(std::addressof(*current))) Value(value); } return current; } catch (...) { for (; first != current; ++first) { first->~Value(); } throw; } } | 
[edit] 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_n(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
[edit] See also
| copies an object to an uninitialized area of memory, defined by a range (function template) | 


