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

ID: Q170198

The information in this article applies to:

The Standard C++ Library, used with:
- Microsoft Visual C++, 32-bit Editions, versions 4.2, 5.0, 6.0

SUMMARY

The sample code below illustrates how to use the gslice::length, gslice::start, and 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 versus 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


    #if _MSC_VER > 1020 // if later than VC++ 4.2
    using namespace std;   // the std C++ libs are in namespace 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.

Keywords : kbcode kbVC420 kbVC500 kbVC600 kbDSupport STLIss
Version : winnt:4.2,5.0,6.0
Platform : winnt
Issue type : kbhowto