Q156347: INFO: STL Sample for the generate_n Function

Article: Q156347
Product(s): Microsoft C Compiler
Version(s): 4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbcode kbVC420 kbVC500 kbVC600 kbDSupport
Last Modified: 26-MAR-2002

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The information in this article applies to:

- The Standard C++ Library, used with:
   - Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 5.0, 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 5.0, 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
   - Microsoft Visual C++.NET (2002) 
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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++.

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  }

REFERENCES
==========

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.

Additional query words: STL STLSample generate_n begin end size

======================================================================
Keywords          : kbcode kbVC420 kbVC500 kbVC600 kbDSupport 
Technology        : kbVCsearch kbAudDeveloper kbVCNET kbVCLibrary
Version           : :4.2,5.0,6.0
Issue type        : kbinfo

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