HOWTO: Quick Sorting Using MFC CArray-Derived Classes
ID: Q216858
The information in this article applies to:
Microsoft Visual C++, 32-bit Editions, versions 5.0, 6.0
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
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:
};
To the public section of your class add the following function:
void Sort(STRINGCOMPAREFN pfnCompare = Compare);
To the protected section of your class add the following static function:
static int __cdecl Compare(const CString * pstr1, const CString * pstr2);
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);
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.
Send feedback to MSDN.
Look here for MSDN Online resources .
