Enhanced collection template classes: CArrayEx, CMapEx and CSortedArray

WEBINAR: On-demand webcast

How to Boost Database Development Productivity on Linux, Docker, and Kubernetes with Microsoft SQL Server 2017 REGISTER >

Environment: WinNT, VC 6.0

This article describes three enhanced collection template classes, CArrayEx, CMapEx and CSortedArrayCArrayEx and CMapEx each provide an assignment operator and class copy constructor that allow us to easily craft two dimensional arrays and mappings.  In addition, CMapEx provides the ability to map CStrings, by providing a template hash function.  CSortedArray is a dynamic array template class that provides "sort after insertion" functionality.

Motivation for CArrayEx, CMapEx

Many of us have tried to create a 2 dimensional array using MFC's standard CArray class, only to encounter the following error:
error C2582: 'operator =' function is unavailable

Example 1:

  typedef CArray <int,int> CIntArray;
  CArray<CIntArray, CIntArray &> a2D;
  CIntArray aInt;

  a2D.Add (aInt);   // error C2582 ****

Example 2:

  typedef CMap<int,int,int,int> CIntMap;
  CMap<int,int,CIntMap,CIntMap &> m2D;
  CIntMap mInt;

  m2D.SetAt (1, mInt);   // error C2582 ****

The error occurs because CArray doesn't have copy a constructor and an assignment operator.  The need for these is obvious.  If we create array of pointers [CArray<void,void>], we need to copy not only the pointer, but also the values.  Microsoft refers us to their knowledge base articles "Collection Class Helpers" and "Collections: How to Make a Type-Safe Collection" for more information.

The problem is solved using CArrayEx:

  typedef CArrayEx<int,int> CIntArray;
  CArrayEx<CIntArray, CIntArray &> a2D;
  CIntArray aInt;

  a2D.Add (aInt);    // OK

and by using CMapEx:

  typedef CMapEx<int,int,int,int> CIntMap;
  CMapEx<int,int,CIntMap,CIntMap &> m2D;
  CIntMap mInt;

  m2D.SetAt (1, mInt);    // OK

Another motivation for CMapEx

If you've tried to create a mapping (using CMap) with a CString key, you'd have encountered the following error:

  CMap<CString,CString,int,int> a;
  a.SetAt (CString("a"), 1);
  // error: cannot convert from 'class CString' to 'unsigned long'

This happens because there's no function to hash a CString to an unsigned long.  CMapEx addresses this problem by providing a HashKey() function.

  template<> inline UINT AFXAPI HashKey<CString> (CString strKey)
  {
    LPCSTR key = strKey;
    UINT nHash = 0;
    while (*key)
          nHash = (nHash<<5) + nHash + *key++;
    return nHash;
  }

Motivation for CSortedArray

CSortedArray allows you to easily find data (by doing a binary search) because it maintains itself in sorted order.

Downloads

Download demo project - 17 Kb


Comments

Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • The need for swift digital transformation is leading to broader utilization of hybrid IT infrastructure by financial services organizations. Banks, investment firms and insurance companies continue to leverage a mix of premises-based and cloud–based technology infrastructure to dramatically improve operational performance, and are networking distributed resources to create business value. Read this white paper to learn why having the right network resources in place is key to benefiting from the cost, …

  • On-demand webcast Continuous integration and continuous deployment (CI/CD) allow DevOps teams to be more efficient. When starting from a production environment, the use of Microsoft SQL Server 2017 in Docker containers and Kubernetes clusters can facilitate a DevOps CI/CD pipeline. Using SQL Server tools also allows you to easily integrate core DevOps application lifecycle management practices to database development. Watch this on-demand presentation to learn how defining the database dependency as …

Most Popular Programming Stories

More for Developers

RSS Feeds

Thanks for your registration, follow us on our social networks to keep up-to-date