C++ concepts: RandomNumberEngine
From cppreference.com
A random number engine is a function object returning unsigned integer values such that each value in the range of possible results has (ideally) equal probability.
Any random number engine is also a UniformRandomBitGenerator
, and therefore may be plugged into any random number distribution in order to obtain a random number (formally, a random variate).
[edit] Requirements
A type E
satisfying UniformRandomBitGenerator
will additionally satisfy RandomNumberEngine
if, given

T
, the type named byE::result_type

s
, a value of typeT

e
, a nonconst value of typeE

v
, an lvalue of typeE

x
andy
, possibly const values of typeE

q
, a lvalue of some type satisfyingSeedSequence

z
, a value of typeunsigned long long

os
, an output stream 
is
, an input stream
the following expressions are valid and have their specified effects:
Expression  Return type  Requirements 

E()  Creates an engine with the same state as all other defaultconstructed engines of type E .
 
E(x)  Creates an engine with the same state as x .
 
E(s)  Creates an engine whose initial state is determined by the integer s .
 
E(q)  Creates an engine whose initial state is determined by a single call to q.generate .
 
e.seed()  void

Sets e == E(). 
e.seed(s)  void

Sets e == E(s). 
e.seed(q)  void

Sets e == E(q). 
e()  T

Returns a value in the closed interval [E::min(), E::max()]. Has amortized constant complexity. 
e.discard(z)  void

Advances e 's state as if by z consecutive calls to e() .

x == y  bool

true if x and y are in the same state (such that repeated future calls to x() and y() will produce identical sequences). Otherwise, false .

x != y  bool

!(x == y) 
os << x  decltype(os)&  Writes to os the textual representation of x 's current state. In the output, adjacent numbers are separated by one or more space characters. If os 's fmtflags are not set to ios_base::decios_base::left, the behavior may be undefined.

is >> v  decltype(is)&  Reads from is the textual representation of v 's current state, such that if that state was previously written via os << x, then x == v. If is 's fmtflags are not set to ios_base::dec, the behavior may be undefined.

[edit] Standard library
The following standard library facilities satisfy RandomNumberEngine
:
(C++11) 
implements linear congruential algorithm (class template) 
(C++11) 
implements Mersenne twister algorithm (class template) 
(C++11) 
implements a subtractwithcarry ( lagged Fibonacci) algorithm (class template) 
(C++11) 
discards some output of a random number engine (class template) 
(C++11) 
packs the output of a random number engine into blocks of a specified number of bits (class template) 
(C++11) 
delivers the output of a random number engine in a different order (class template) 
The following standard library facilities satisfy UniformRandomBitGenerator
but not RandomNumberEngine
:
nondeterministic random number generator using hardware entropy source (class) 