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

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

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;
   };

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

REFERENCES

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