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

Article ID:156347
Last Review:July 15, 2005
Revision:4.0
This article was previously published under Q156347
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SUMMARY

The sample code below illustrates how to use the generate_n, begin, end, and size STL functions in Visual C++.

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MORE INFORMATION

Required header

   <algorithm>

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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.

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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.

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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  }

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REFERENCES

For the same topic about generate_n, visit the following MSDN Web site: http://msdn.microsoft.com/library/en-us/vclang98/html/sample_generate_n_(STL_Sample).asp?frame=true (http://msdn.microsoft.com/library/en-us/vclang98/html/sample_generate_n_(STL_Sample).asp?frame=true)

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APPLIES TO
The Standard C++ Library, when used with:
  Microsoft Visual C++ 4.2 Enterprise Edition
  Microsoft Visual C++ 5.0 Enterprise Edition
  Microsoft Visual C++ 6.0 Enterprise Edition
  Microsoft Visual C++ 4.2 Professional Edition
  Microsoft Visual C++ 5.0 Professional Edition
  Microsoft Visual C++ 6.0 Professional Edition
  Microsoft Visual C++ 6.0 Standard Edition
  Microsoft Visual C++ .NET 2003 Standard Edition
  Microsoft Visual C++ .NET 2002 Standard Edition

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Keywords: 
kbhowto kbinfo kbstl kbcode kbfunctions KB156347

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