STL Sample for the generate_n Function

ID: Q156347

The information in this article applies to:

• The Standard C++ Library included with: - Microsoft Visual C++, 32-bit Edition, version 4.2

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)

      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

////////////////////////////////////////////////////////////////////// 
// 
// 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

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

// 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 STLIss 
Version           : WINNT:4.2;
Platform          : NT WINDOWS
Issue type        : kbhowto

Last Reviewed: October 10, 1997