Man Page generate_n.3

                       Standard C++ Library
             Copyright 1998, Rogue Wave Software, Inc.

NAME

     generate, generate_n

      - Initialize a container with values produced by  a  value-
     generator class.

SYNOPSIS

     #include <algorithm>

     template <class ForwardIterator, class Generator>
      void generate(ForwardIterator first, ForwardIterator last,
                    Generator gen);

     template <class OutputIterator, class Size, class Generator>
      void generate_n(OutputIterator  first,  Size  n,  Generator
      gen);

DESCRIPTION

     A value-generator function returns a value each time  it  is
     invoked.  The  algorithms generate and generate_n initialize
     (or reinitialize) a sequence by assigning the  return  value
     of the generator function gen to all the elements designated
     by iterators in the range [first, last) or [first,  first  +
     n). The function gen takes no arguments. (gen can be a func-
     tion or a class with an operator () defined  that  takes  no
     arguments.)

     generate_n assumes that there are at least n  elements  fol-
     lowing first, unless first is an insert iterator.

COMPLEXITY

     The generate and generate_n algorithms invoke gen and assign
     its return value exactly last - first (or n) times.

EXAMPLE

     //
     // generate.cpp
     //
      #include <algorithm>
      #include <vector>
      #include <iostream>
     using namespace std;

      // Value generator simply doubles the current value
      // and returns it
     template <class T>
     class generate_val
      {
       private:
          T val_;
       public:
          generate_val(const T& val) : val_(val) {}
          T& operator()() { val_ += val_; return val_; }
      };

     int main()
      {
       int d1[4] = {1,2,3,4};
       generate_val<int> gen(1);

        // Set up two vectors
       vector<int> v1(d1,d1 + 4), v2(d1,d1 + 4);
        // Set up one empty vector
       vector<int> v3;

        // Generate values for all of v1
        generate(v1.begin(),v1.end(),gen);

        // Generate values for first 3 of v2
        generate_n(v2.begin(),3,gen);

        // Use insert iterator to generate 5 values for v3
        generate_n(back_inserter(v3),5,gen);

        // Copy all three to cout
       ostream_iterator<int,char> out(cout," ");
       copy(v1.begin(),v1.end(),out);
       cout << endl;
       copy(v2.begin(),v2.end(),out);
       cout << endl;
       copy(v3.begin(),v3.end(),out);
       cout << endl;

        // Generate 3 values for cout
        generate_n(ostream_iterator<int>(cout," "),3,gen);
       cout << endl;

       return 0;

      }

     Program Output




     2 4 8 16
     2 4 8 4
     2 4 8 16 32
     2 4 8

WARNINGS

     If your compiler does not support default  template  parame-
     ters,  then you always need to supply the Allocator template
     argument. For instance, you have to write:

     vector<int, allocator<int> >

     instead of:

     vector<int>

     If your compiler does not support namespaces,  then  you  do
     not need the using declaration for std.

SEE ALSO

     Function_Objects