seed_seq Class

Article
08/03/2021

Stores a vector of unsigned integer values that can supply a randomized seed for a random-number engine.

Syntax

class seed_seq
   {
public:
   // types
   typedef unsigned int result_type;

   // constructors
   seed_seq();
   template <class T>
      seed_seq(initializer_list<T> initlist);
   template <class InputIterator>
      seed_seq(InputIterator begin, InputIterator end);

   // generating functions
   template <class RandomAccessIterator>
      void generate(RandomAccessIterator begin, RandomAccessIterator end);

   // property functions
   size_t size() const;
   template <class OutputIterator>
      void param(OutputIterator dest) const;

   // no copy functions
   seed_seq(const seed_seq&) = delete;
   void operator=(const seed_seq&) = delete;
   };

Types

typedef unsigned int result_type;

The type of the elements of the seed sequence. A 32-bit unsigned integer type.

Constructors

seed_seq();

Default constructor, initializes to have an empty internal sequence.

template<class T>
seed_seq(initializer_list<T> initlist);

Uses initlist to set the internal sequence. T must be an integer type.

template<class InputIterator>
seed_seq(InputIterator begin, InputIterator end);

Initializes the internal sequence using all elements in the input iterator range provided. iterator_traits<InputIterator>::value_type must be an integer type.

Members

Generating Functions

template<class RandomAccessIterator>
void generate(RandomAccessIterator begin,
          RandomAccessIterator end);

Populates the elements of the provided sequence using an internal algorithm. This algorithm is affected by the internal sequence with which seed_seq was initialized. Does nothing if begin == end.

Property Functions

size_t size() const;

Returns the number of elements in the seed_seq.

template<class OutputIterator>
void param(OutputIterator dest) const;

Copies the internal sequence into the output iterator dest.

Example

The following code example exercises the three constructors and generates output from the resulting seed_seq instances when assigned to an array. For an example that uses seed_seq with a random number generator, see <random>.

#include <iostream>
#include <random>
#include <string>
#include <array>

using namespace std;

void test(const seed_seq& sseq) {
    cout << endl << "seed_seq::size(): " << sseq.size() << endl;

    cout << "seed_seq::param(): ";
    ostream_iterator<unsigned int> out(cout, " ");
    sseq.param(out);
    cout << endl;

    cout << "Generating a sequence of 5 elements into an array: " << endl;
    array<unsigned int, 5> seq;
    sseq.generate(seq.begin(), seq.end());
    for (unsigned x : seq) { cout << x << endl; }
}

int main()
{
    seed_seq seed1;
    test(seed1);

    seed_seq seed2 = { 1701, 1729, 1791 };
    test(seed2);

    string sstr = "A B C D"; // seed string
    seed_seq seed3(sstr.begin(), sstr.end());
    test(seed3);
}

seed_seq::size(): 0
seed_seq::param():
Generating a sequence of 5 elements into an array:
505382999
163489202
3932644188
763126080
73937346

seed_seq::size(): 3
seed_seq::param(): 1701 1729 1791
Generating a sequence of 5 elements into an array:
1730669648
1954224479
2809786021
1172893117
2393473414

seed_seq::size(): 7
seed_seq::param(): 65 32 66 32 67 32 68
Generating a sequence of 5 elements into an array:
3139879222
3775111734
1084804564
2485037668
1985355432

Remarks

Member functions of this class do not throw exceptions.

Requirements

Header: <random>

Namespace: std

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