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std::seed_seq::seed_seq

From cppreference.com
< cpp‎ | numeric‎ | random‎ | seed seq
 
 
 
 
 
seed_seq() noexcept;
(1) (since C++11)
seed_seq( const seed_seq& ) = delete;
(2) (since C++11)
template< class InputIt >
seed_seq( InputIt begin, InputIt end );
(3) (since C++11)
template< class T >
seed_seq( std::initializer_list<T> il );
(4) (since C++11)
1) The default constructor. After construction, v is empty.
2) The copy constructor is deleted: std::seed_seq is not copyable.
3) Constructs a std::seed_seq with the values in the range [beginend). Equivalent to default-initializing v  followed by for (InputIt s = begin; s != end; ++s)
    v .push_back(modseed(*s));
, where mod_seed(x)=x mod 232
.
If std::iterator_traits<InputIt>::value_type is not an integer type, the program is ill-formed.
If InputIt does not satisfy the requirements of LegacyInputIterator, the behavior is undefined.
4) Equivalent to seed_seq(il.begin(), il.end()). This constructor enables list-initialization from the list of seed values.
This overload participates in overload resolution only if T is an integer type.

[edit] Parameters

begin, end - the pair of iterators denoting the initial seed sequence
il - the initial seed sequence

[edit] Example

#include <iterator>
#include <random>
#include <sstream>
 
int main()
{
    std::seed_seq s1; // default-constructible
    std::seed_seq s2{1, 2, 3}; // can use list-initialization
    std::seed_seq s3 = {-1, 0, 1}; // another form of list-initialization
    int a[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    std::seed_seq s4(a, a + 10); // can use iterators
    std::istringstream buf("1 2 3 4 5"); 
    std::istream_iterator<int> beg(buf), end;
    std::seed_seq s5(beg, end); // even stream input iterators
}

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2180 C++11 all constructors were non-throwing only overload (1) is non-throwing
LWG 3422 C++11 1. overload (1) was not noexcept
2. overload (4) was not constrainted
1.made noexcept
2. constrained