[rand.req.eng] (original) (raw)

A class Ethat meets the requirements of a uniform random bit generatoralso meets the requirements of a random number engineif the expressions shown in Table 94are valid and have the indicated semantics, and if E also meets all other requirements of this subclause [rand.req.eng].

Table 94: Random number engine requirements [tab:rand.req.eng]

Expression	Return type	Pre/post-condition	Complexity
E()	Creates an engine with the same initial state as all other default-constructed engines of type E.
E(x)	Creates an engine that compares equal to x.
E(s)	Creates an engine with initial state determined by s.
E(q)241	Creates an engine with an initial state that depends on a sequence produced by one call to q.generate.	same as complexity of q.generate called on a sequence whose length is size of state
e.seed()	void	Postconditions: e == E().	same as E()
e.seed(s)	void	Postconditions: e == E(s).	same as E(s)
e.seed(q)	void	Postconditions: e == E(q).	same as E(q)
e()	T	Advances e's state e toe e) and returnsGA(e).	per [rand.req.urng]
e.discard(z) 242	void	Advances e's state e to by any means equivalent to z consecutive calls e().	no worse than the complexity of z consecutive calls e()
x == y	bool	This operator is an equivalence relation. With and as the infinite sequences of values that would be generated by repeated future calls to x() and y(), respectively, returns true if ; else returns false.
x != y	bool	!(x == y).
os << x	reference to the type of os	With os.fmtflags set toios_base::dec\|ios_base::left and the fill character set to the space character, writes to os the textual representation of x's current state. In the output, adjacent numbers are separated by one or more space characters.Postconditions: The os.fmtflags and fill character are unchanged.
is >> v	reference to the type of is	With is.fmtflags set to ios_base::dec, sets v's state as determined by reading its textual representation from is. If bad input is encountered, ensures that v's state is unchanged by the operation and calls is.setstate(ios_base::failbit) (which may throw ios_base::failure ([iostate.flags])). If a textual representation written via os << x was subsequently read via is >> v, then x == v provided that there have been no intervening invocations of x or of v.Preconditions: is provides a textual representation that was previously written using an output stream whose imbued locale was the same as that of is, and whose type's template specialization argumentscharT and traits were respectively the same as those of is.Postconditions: The is.fmtflags are unchanged.