seed_seq Class
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