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generate_n (STL Samples) 

Illustrates how to use the generate_n Standard Template Library (STL) function in Visual C++.


template<class OutputIterator, class Size, class Generator> inline
   void generate_n(
      OutputIterator First,
      Size n,
      Generator Gen
   )
NoteNote

The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.

The generate_n algorithm traverses the range [First, First + n), assigning to each element the value returned by Gen. Note that generate modifies the elements in the specified range.

// generate_n.cpp
// compile with: /EHsc
//
// Functions:
//   generate_n  - Fill a specified number of elements of a sequence
//                 using a generator function.
//
//   begin       - Returns an iterator that points to the first element
//                 in a sequence.
//
//   end         - Returns an iterator that points one past the end of
//                 a sequence.
//
//   size        - Returns the length of a sequence.

// disable warning C4786: symbol greater than 255 characters,
// okay to ignore
#pragma warning(disable: 4786)

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

// return the next Fibonacci number in the
// Fibonacci series.
int Fibonacci(void)
{
    static int r;
    static int f1 = 0;
    static int f2 = 1;
    r = f1 + f2 ;
    f1 = f2 ;
    f2 = r ;
    return f1 ;
}

int main()
{
    const int VECTOR_SIZE = 15 ;

    // Define a template class vector of integers
    typedef vector<int > IntVector ;

    //Define an iterator for template class vector of integer
    typedef IntVector::iterator IntVectorIt ;

    IntVector Numbers(VECTOR_SIZE) ;   //vector containing numbers

    IntVectorIt start, end, it ;

    int i ;

    //Initialize vector Numbers
    for(i = 0; i < VECTOR_SIZE; i++)
        Numbers[i] = i * i ;

    start = Numbers.begin() ;   // location of first
                                // element of Numbers

    end = Numbers.end() ;       // one past the location
                                // last element of Numbers

    cout << "Before calling generate_n" << endl ;

    // print content of Numbers
    cout << "Numbers { " ;
    for(it = start; it != end; it++)
        cout << *it << " " ;
    cout << " }\n" << endl ;

    // fill the specified range with a series of
    // Fibonacci numbers using the Fibonacci function
    generate_n(start + 5, Numbers.size() - 5, Fibonacci) ;

    cout << "After calling generate_n" << endl ;

    // print content of Numbers
    cout << "Numbers { " ;
    for(it = start; it != end; it++)
        cout << *it << " " ;
    cout << " }\n" << endl ;
}
Before calling generate_n
Numbers { 0 1 4 9 16 25 36 49 64 81 100 121 144 169 196  }

After calling generate_n
Numbers { 0 1 4 9 16 1 1 2 3 5 8 13 21 34 55  }

Header: <algorithm>

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