HOWTO: Quick Sorting Using MFC CArray-Derived Classes

ID: Q216858

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The information in this article applies to:

• Microsoft Visual C++, 32-bit Editions, versions 5.0, 6.0

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SUMMARY

This article shows you how to quick-sort an MFC CArray-derived class. The code below depends only on the MFC and Visual C++ run-time library.

MORE INFORMATION

The Visual C++ run-time library (MSVCRT) implements the quick-sort function, qsort, as follows:

void qsort( void *base, size_t num, size_t width, int (__cdecl *compare )(const void *elem1, const void *elem2 ) ); 

The following example shows you how to use this function to sort an MFC CArray class. Although the following example uses a CString array, you can easily customize for other MFC CArray-derived classes, such as CByteArray, CDWordArray, CObArray, CPtrArray, CUintArray, and CWordArray.

Steps to Implement Sorting

1. Derive your array data class from one of the CArray-derived classes. In our example, we use CStringArray as the base class for our class. The following is the declaration in the header file:
   
   

   
   
   class CSortableStringArray : public CStringArray
   
   {
   
   public:
   
   protected:
   
   }; 

   
   
   
2. To the public section of your class add the following function:
   

   
   
   void Sort(STRINGCOMPAREFN pfnCompare = Compare); 

   
   
   
3. To the protected section of your class add the following static function:
   

   
   
   static int __cdecl Compare(const CString * pstr1, const CString * pstr2); 

   
   
   
4. Now add the following two type defs above the declaration of your class. These typedefs later help us in passing pointers of the two functions that we declared in steps 2 and 3 to the Visual C++ run-time's qsort function:
   
   

   
   
   typedef int (__cdecl *GENERICCOMPAREFN)(const void * elem1, const void * elem2);
   
   typedef int (__cdecl *STRINGCOMPAREFN)(const CString * elem1, const CString * elem2); 

   
   
   
5. In your .cpp file, implement the two functions that you declared earlier:
   

   
   
   // 
   
   // SortableStringArray.cpp
   
   // 
   
   
   
   int CSortableStringArray::Compare(const CString * pstr1, const CString * pstr2)
   
   {
   
   	ASSERT(pstr1);
   
   	ASSERT(pstr2);
   
   	return pstr1->Compare(*pstr2);
   
   }
   
   
   
   void CSortableStringArray::Sort(STRINGCOMPAREFN pfnCompare /*= CSortedStringArray::Compare */)
   
   {
   
   	CString * prgstr = GetData();
   
   	qsort(prgstr,GetSize(),sizeof(CString),(GENERICCOMPAREFN)pfnCompare);
   
   } 

   
   
   

That is it. Now let's look at the contents of the entire file:

// 

// SortableStringArray.h

// 



typedef int (__cdecl *GENERICCOMPAREFN)(const void * elem1, const void * elem2);

typedef int (__cdecl *STRINGCOMPAREFN)(const CString * elem1, const CString * elem2);



class CSortableStringArray : public CStringArray

{

public:

	void Sort(STRINGCOMPAREFN pfnCompare = Compare);



protected:

	static int __cdecl Compare(const CString * pstr1, const CString * pstr2);

};



// 

// SortableStringArray.cpp

// 



#include "SortableStringArray.h"



int CSortableStringArray::Compare(const CString * pstr1, const CString * pstr2)

{

	ASSERT(pstr1);

	ASSERT(pstr2);

	return pstr1->Compare(*pstr2);

}



void CSortableStringArray::Sort(STRINGCOMPAREFN pfnCompare /*= CSortedStringArray::Compare */)

{

	CString * prgstr = GetData();

	qsort(prgstr,GetSize(),sizeof(CString),(GENERICCOMPAREFN)pfnCompare);

} 

To use the array in your code, just declare it and call the Sort() function. The following example uses this array:

	srand( (unsigned)time( NULL ) ); // Generate seed for rand().

	CSortableStringArray arr;

	CString str;

	for (int i=0; i< 1000;i++)

	{

		str.Format("%6d", rand());// Get a random number string.		

		arr.Add(str);

		TRACE("%s\n", (LPCTSTR)str);

	}

	long ltim=GetTickCount();

	arr.Sort();

	for (i=0; i< 1000;i++)

	{

		TRACE("%s\n", (LPCTSTR)arr[i]);

	}



	TRACE("Time took= %li\n", GetTickCount()-ltim); 

NOTE: To implement a CArray type other than CString, just derive your class from the other array types and modify the Sort() and the Compare() functions accordingly.

NOTE: Quick Sort is a more efficient mechanism of sorting than the bubble sort used in the Microsoft Knowledge Base article, "How to Sort a CStringArray in MFC" (Q120961)

REFERENCES

For additional information about the bubble sort method, please see the following article in the Microsoft Knowledge Base:

Q120961 How to Sort a CStringArray in MFC

Additional query words:

Keywords : kbDatabase kbMFC kbODBC kbVC500 kbVC600
Version : winnt:5.0,6.0
Platform : winnt
Issue type : kbhowto

Last Reviewed: February 4, 2000
© 2000 Microsoft Corporation. All rights reserved. Terms of Use.

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