generate_n and int sequence : generate_n « STL Algorithms Modifying sequence operations « C++

1. C++
2. STL Algorithms Modifying sequence operations
3. generate_n

generate_n and int sequence

 
 
/* The following code example is taken from the book
 * "The C++ Standard Library - A Tutorial and Reference"
 * by Nicolai M. Josuttis, Addison-Wesley, 1999
 *
 * (C) Copyright Nicolai M. Josuttis 1999.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
#include <iostream>
#include <list>
#include <algorithm>

using namespace std;

/* PRINT_ELEMENTS()
 * - prints optional C-string optcstr followed by
 * - all elements of the collection coll
 * - separated by spaces
 */
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
    typename T::const_iterator pos;

    std::cout << optcstr;
    for (pos=coll.begin(); pos!=coll.end(); ++pos) {
        std::cout << *pos << ' ';
    }
    std::cout << std::endl;
}


class IntSequence {
  private:
    int value;
  public:
    // constructor
    IntSequence (int initialValue)
     : value(initialValue) {
    }

    // ''function call''
    int operator() () {
        return value++;
    }
};

int main()
{
    list<int> coll;
    IntSequence seq(1);    // integral sequence starting with 1

    // insert values from 1 to 4
    // - pass function object by reference
    //     so that it will continue with 5
    generate_n<back_insert_iterator<list<int> >,
               int, IntSequence&>(back_inserter(coll),    // start
                                  4,      // number of elements
                                  seq);   // generates values
    PRINT_ELEMENTS(coll);

    // insert values from 42 to 45
    generate_n (back_inserter(coll),      // start
                4,                        // number of elements
                IntSequence(42));         // generates values
    PRINT_ELEMENTS(coll);

    // continue with first sequence
    // - pass function object by value
    //     so that it will continue with 5 again
    generate_n (back_inserter(coll),      // start
                4,                        // number of elements
                seq);                     // generates values
    PRINT_ELEMENTS(coll);
    
    // continue with first sequence again
    generate_n (back_inserter(coll),      // start
                4,                        // number of elements
                seq);                     // generates values
    PRINT_ELEMENTS(coll);
}
/* 
1 2 3 4
1 2 3 4 42 43 44 45
1 2 3 4 42 43 44 45 5 6 7 8
1 2 3 4 42 43 44 45 5 6 7 8 5 6 7 8

 */
        
  

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