28 Numerics library [numerics]

28.5 Random number generation [rand]

28.5.4 Random number engine class templates [rand.eng]

28.5.4.1 General [rand.eng.general]

Each type instantiated from a class template specified in [rand.eng] meets the requirements of a random number engine type.
Except where specified otherwise, the complexity of each function specified in [rand.eng] is constant.
Except where specified otherwise, no function described in [rand.eng] throws an exception.
Every function described in [rand.eng] that has a function parameter q of type Sseq& for a template type parameter named Sseq that is different from type seed_­seq throws what and when the invocation of q.generate throws.
Descriptions are provided in [rand.eng] only for engine operations that are not described in [rand.req.eng] or for operations where there is additional semantic information.
In particular, declarations for copy constructors, for copy assignment operators, for streaming operators, and for equality and inequality operators are not shown in the synopses.
Each template specified in [rand.eng] requires one or more relationships, involving the value(s) of its non-type template parameter(s), to hold.
A program instantiating any of these templates is ill-formed if any such required relationship fails to hold.
For every random number engine and for every random number engine adaptor X defined in [rand.eng] and in [rand.adapt]:
  • if the constructor template<class Sseq> explicit X(Sseq& q); is called with a type Sseq that does not qualify as a seed sequence, then this constructor shall not participate in overload resolution;
  • if the member function template<class Sseq> void seed(Sseq& q); is called with a type Sseq that does not qualify as a seed sequence, then this function shall not participate in overload resolution.
The extent to which an implementation determines that a type cannot be a seed sequence is unspecified, except that as a minimum a type shall not qualify as a seed sequence if it is implicitly convertible to X​::​result_­type.