How to use the generate_n, begin, end, and size Standard Template Library (STL) functions in Visual C++ (156347)

MORE INFORMATION

Required header

   <algorithm>

Prototype

   template<class OutputIterator, class Size, class Generator> inline

         void generate_n(OutputIterator first, Size n, Generator gen)

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

Description

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.

Sample code

Note In the first line of the sample code section, /GX is equivalent to /EHsc in VC++ .NET and is set by default.

////////////////////////////////////////////////////////////////////// 
// 
// Compile options needed: /GX
// 
// generate_n.cpp : Illustrates how to use the generate_n function.
// 
// 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.
// 
// Written by Kalindi Sanghrajka
// of Microsoft Product Support Services,
// Software Core Developer Support.
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
////////////////////////////////////////////////////////////////////// 

// disable warning C4786: symbol greater than 255 character,
// okay to ignore

#pragma warning(disable: 4786)

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

#if _MSC_VER > 1020   // if VC++ version is > 4.2
   using namespace std;  // std c++ libs implemented in std
   #endif

// 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 ;

}

void main()

{

    const int VECTOR_SIZE = 15 ;

    // Define a template class vector of integers
    typedef vector<int, allocator<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 ;

}

Program Output is:

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  }