From cppreference.com
Defined in header
template<classNoThrowForwardIt,classSize,classT>NoThrowForwardItuninitialized_fill_n(NoThrowForwardItfirst,Sizecount,constT&value); (1)(constexpr since C++26)template<classExecutionPolicy,classNoThrowForwardIt,classSize,classT>NoThrowForwardItuninitialized_fill_n(ExecutionPolicy&&policy,NoThrowForwardItfirst,Sizecount,constT&value); (2) (since C++17)1) Constructs the first count elements in the destination range beginning at first with the given value value as if by
for(;count--;++first)
::new(
(*first))
typenamestd::iterator_traits<NoThrowForwardIt>::value_type(value);
returnfirst;
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 participates in overload resolution only if the value of the following expression is true:
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
(until C++20)std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
(since C++20)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 -NoThrowForwardIt must meet the requirements of
. -No increment, assignment, comparison, or indirection through valid instances of NoThrowForwardIt may throw exceptions. Applying &* to a NoThrowForwardIt value must yield a pointer to its value type.(until C++11)Return value
As described above.
Exceptions
2) During the execution process:
If the temporary memory resources required for parallelization are not available,
is thrown.
If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for
,
is invoked).
Notes
macroValueStdFeature
__cpp_lib_raw_memory_algorithms
(C++26)constexpr for
specialized <memory> algorithms
, (
)Possible implementation
template<classNoThrowForwardIt,classSize,classT>constexprNoThrowForwardItuninitialized_fill_n(NoThrowForwardItfirst,Sizecount,constT&value){usingV=typenamestd::iterator_traits<NoThrowForwardIt>::value_type;NoThrowForwardItcurrent=first;try{for(;count>0;++current,(void)--count)::new(static_cast<void*>(std::addressof(*current)))V(value);returncurrent;}catch(...){for(;first!=current;++first)first->~V();throw;}returncurrent;}Example
Run this code
#include<algorithm>#include<iostream>#include<memory>#include<string>#include<tuple>intmain(){std::string*p;std::size_tsz;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 Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++98 given T as the value type of NoThrowForwardIt, if
T::operatornew exists, the program might be ill-formed uses global placement new instead
C++98 the location of the first element following
the filling range was not returned returned
C++11 this algorithm might be hijacked by overloaded operator&uses
See also