A discard_block_engine random number engine adaptor
produces random numbers
selected from those produced by some base engine e.

The state
x
of a discard_block_engine engine adaptor object x
consists of the state e of its base engine e
and an additional integer n.

The state transition is performed as follows:
If ,
advance the state of e from e to e
and set n to 0.

The generation algorithm
yields the value returned by the last invocation of e()
while advancing e's state as described above.

template<class Engine, size_t p, size_t r>
class discard_block_engine {
public:
// types
using result_type = typename Engine::result_type;
// engine characteristics
static constexpr size_t block_size = p;
static constexpr size_t used_block = r;
static constexpr result_type min() { return Engine::min(); }
static constexpr result_type max() { return Engine::max(); }
// constructors and seeding functions
discard_block_engine();
explicit discard_block_engine(const Engine& e);
explicit discard_block_engine(Engine&& e);
explicit discard_block_engine(result_type s);
template<class Sseq> explicit discard_block_engine(Sseq& q);
void seed();
void seed(result_type s);
template<class Sseq> void seed(Sseq& q);
// generating functions
result_type operator()();
void discard(unsigned long long z);
// property functions
const Engine& base() const noexcept { return e; };
private:
Engine e; // exposition only
int n; // exposition only
};
In addition to its behavior
pursuant to subclause [rand.req.adapt],
each constructor
that is not a copy constructor
sets n to 0.