seed_seq Class

2018-01-02

The latest version of this topic can be found at seed_seq Class.

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);  
}

Output

  
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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