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Q168185: HOWTO: STL Sample for gslice::(length, start, stride) Functions

Article: Q168185
Product(s): Microsoft C Compiler
Version(s): winnt:4.2,5.0,6.0
Operating System(s): 
Keyword(s): _IK kbVC420 kbVC500 kbVC600
Last Modified: 05-MAY-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- The Standard C++ Library, used with:
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
-------------------------------------------------------------------------------

SUMMARY
=======

The sample code below illustrates how to use the gslice::length, gslice::start,
gslice::stride STL functions in Visual C++.

Note that there are some differences in the implementation of the Standard C++
Library components in Visual C++ version 4.2 vs. later revisions. The relevant
sections of code below compile conditionally based upon the value of _MSC_VER.

MORE INFORMATION
================

Required Header
---------------

     <valarray>

Prototype
---------

     class gslice
     {
     public:

        gslice();
        gslice(size_t st, const valarray<size_t> len,
                    const valarray<size_t> str);
        size_t start() const;

     #if _MSC_VER == 1020   // if VC++ 4.2, define length()

        const valarray<size_t> length() const;

     #else   // if later than VC++ 4.2, define size() instead

        const valarray<size_t> size() const;

     #endif

        const valarray<size_t> stride() const;

     };

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

Description
-----------

This sample demostrates the use of STL gslice array to change "Hello World!"
string to "Hello There." string.

Sample Code
-----------

      ////////////////////////////////////////////////////////////////////// 
      // 
      // Compile options needed: None
      // 
      // <filename> :  main.cpp
      // 
      // Functions:
      // 
      //  gslice::length, gslice::start, gslice::stride
      // 
      // Written by Yeong-Kah Tam
      // of Microsoft Product Support Services,
      // Copyright (c) 1996 Microsoft Corporation. All rights reserved.
      ////////////////////////////////////////////////////////////////////// 

      #include <iostream>            // for i/o functions
      #include <valarray>            // for valarray
      using namespace std;

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

      void main()
      {
         // Initialize string 1 to contain "Hello World!", and string 2 to
         // contain "There".
         valarray<char> string1("Hello World!", 12);
         valarray<char> string2("There.", 6);

         // Display both strings...
         cout << "String 1 = ";
         int strlen;
      #if _MSC_VER == 1020   // VC++ 4.2 - call length()
         strlen = string1.length();
      #else   // later than VC++ 4.2 - call size()
         strlen = string1.size();
      #endif
         for (int i = 0; i < strlen; i++)
            cout << string1[i];
         cout << "\r\n";

         cout << "String 2 = ";
      #if _MSC_VER == 1020   // VC++ 4.2 - call length()
         strlen = string2.length();
      #else   // later than VC++ 4.2 - call size()
         strlen = string2.size();
      #endif
         for (i = 0; i < strlen; i++)
            cout << string2[i];
         cout << "\r\n\r\n";

         // Create 2 vectors for use by gslice().
         const size_t lv[] = {2, 3};   // number of initial indexes
         const size_t dv[] = {3, 1};   // increment value
         const valarray<size_t> len(lv, 2), stride(dv, 2);

         // gslice(6, len, stride) creates a gslice
              // array of {6, 7, 8, 9, 10, 11} which is used to select the
              // elements of string1.  "World!" it is. In turn, these
              // elements are replaced by the corresponding element
         // in string2.
         gslice gslice_obj(6, len, stride);
         string1[gslice_obj] = string2;

         // Display starting index, length vector, and stride vector of
              // the gslice object.
         cout << "gslice - starting index = " << gslice_obj.start()
                << "\r\n";

      #if _MSC_VER == 1020   // VC++ 4.2 - call length()
         valarray<size_t> gslice_len = gslice_obj.length();
         strlen = gslice_len.length();
      #else   // later than VC++ 4.2 - call size()
         valarray<size_t> gslice_len = gslice_obj.size();
         strlen = gslice_len.size();
      #endif
         cout << "gslice - length vector  = ";
         for (i = 0; i < strlen; i++)
            cout << gslice_len[i] << "  ";
         cout << "\r\n";

         valarray<size_t> gslice_stride = gslice_obj.stride();
      #if _MSC_VER == 1020   // VC++ 4.2 - call length()
         strlen = gslice_stride.length();
      #else   // later than VC++ 4.2 - call size()
         strlen = gslice_stride.size();
      #endif
         cout << "gslice - stride vector  = ";
         for (i = 0; i < strlen; i++)
            cout << gslice_stride[i] << "  ";
         cout << "\r\n\r\n";

         // Now print out the result.
         cout << "After the change, String 1 = ";
      #if _MSC_VER == 1020   // VC++ 4.2 - call length()
         strlen = string1.length();
      #else   // later than VC++ 4.2 - call size()
         strlen = string1.size();
      #endif
         for(i = 0; i < strlen; i++)
            cout << string1[i];
         cout << "\r\n";
      }

Program Output
--------------

  String 1 = Hello World!
  String 2 = There.

  gslice - starting index = 6
  gslice - length vector  = 2  3
  gslice - stride vector  = 3  1

After the change, String 1 = Hello There.

REFERENCES
==========

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

(c) Microsoft Corporation 1997, All Rights Reserved. Contributions by Yeong-Kah
Tam, Microsoft Corporation


Additional query words: STL STLSample length, start, stride

======================================================================
Keywords          : _IK kbVC420 kbVC500 kbVC600 
Technology        : kbVCsearch kbAudDeveloper kbVCLibrary
Version           : winnt:4.2,5.0,6.0
Issue type        : kbhowto

=============================================================================

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