Namespaces
Variants

std::mersenne_twister_engine<UIntType,w,n,m,r,a,u,d,s,b,t,c,l,f>:: mersenne_twister_engine

From cppreference.net
C++
Numerics library
Pseudo-random number generation
Random number distributions
Uniform distributions
(C++11)
(C++11)
(C++11)
Bernoulli distributions
(C++11)
(C++11)
(C++11)
(C++11)
Poisson distributions
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
Normal distributions
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
Sampling distributions
(C++11)
(C++11)
(C++11)
std::mersenne_twister_engine
Member functions
mersenne_twister_engine::mersenne_twister_engine
Generation
Characteristics
Non-member functions
(C++11) (C++11) (until C++20)
(C++11) (C++11)
mersenne_twister_engine ( ) : mersenne_twister_engine ( default_seed ) { }
(1) (since C++11)
explicit mersenne_twister_engine ( result_type value ) ;
(2) (since C++11)
template < class SeedSeq >
explicit mersenne_twister_engine ( SeedSeq & seq ) ;
(3) (since C++11)
mersenne_twister_engine ( const mersenne_twister_engine & other ) ;
(4) (since C++11)
(implicitly declared)

Constructs the pseudo-random number engine.

1) The default constructor.
  • If the default-constructed engine is of type std::mt19937 , the 10000th consecutive invocation of it produces the value 4123659995 .
  • If the default-constructed engine is of type std::mt19937_64 , the 10000th consecutive invocation of it produces the value 9981545732273789042 .
2) Constructs the engine with a seed value value . Given 2 w
as p , the engine's initial state is determined as follows:
  1. Sets X -n to value % p .
  2. For each integer i in [ i - n , - 1 ] , sets X i to [f·(X i-1 xor (X i-1 rshift (w-2)))+i mod n] mod p , where xor and rshift stand for built-in bitwise XOR and bitwise right-shift respectively.
3) Constructs the engine with a seed sequence seq . Given std:: size_t ( w / 32 ) + 1 as k , the engine's initial state is determined as follows:
  1. Creates an invented array object a of length n * k .
  2. Calls seq. generate ( a + 0 , a + n * k ) .
  3. For each integer i in [ - n , - 1 ] , sets X i to (∑ k-1
    j=0     a k(i+n)+j ·2 32j
    ) mod 2 w
    .
  4. If the most significant w − r bits of X -n are zero, and if each of the other resulting X i is ​ 0 ​ , changes X -n to 2 w-1
    .
This overload participates in overload resolution only if SeedSeq meets the requirements of SeedSequence .
4) The copy constructor. Upon construction, * this == other is true .

Contents

Parameters

value - seed value to use in the initialization of the internal state
seq - seed sequence to use in the initialization of the internal state

Complexity

1,2) O(n) .
3) Same as the complexity of the seq.generate call.
4) O(n) .

Exceptions

3) If SeedSeq is not std::seed_seq , throws the exceptions thrown by the seq.generate call.

Example

This section is incomplete
Reason: demos for overloads (2-4) required

Run this code 
#include <cassert>
#include <random>
int main()
{
    std::mt19937 gen32; // overload (1)
    std::mt19937_64 gen64; // overload (1)
    gen32.discard(10000 - 1);
    gen64.discard(10000 - 1);
    assert(gen32() == 4123659995);
    assert(gen64() == 9981545732273789042ull);
}

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 2181 C++11 overload ( 3 ) would not throw even if the seq.generate call throws propagates the exception
P0935R0 C++11 the default constructor was explicit made implicit

See also

sets the current state of the engine
(public member function)