This article was contributed by Douglas Peterson.

// SortableObArray.h
/////////////////////////////////////////////////////////////////////

class CSortableObArray : public CObArray
{
public:
	void Sort(int(*CompareFunc)(CObject* pFirst, CObject* pSecond));
	void Sort(int iStartPos, int iElements, int(*CompareFunc)(CObject* pFirst, CObject* pSecond));
};


template< class TYPE >
class CTypedSortableObArray : public CSortableObArray
{
public:
	// Accessing elements
	TYPE GetAt(int nIndex) const
	{ return (TYPE)CSortableObArray::GetAt(nIndex); }
	TYPE& ElementAt(int nIndex)
	{ return (TYPE&)CSortableObArray::ElementAt(nIndex); }
	void SetAt(int nIndex, TYPE ptr)
	{ CSortableObArray::SetAt(nIndex, ptr); }
	
	// Potentially growing the array
	void SetAtGrow(int nIndex, TYPE newElement)
	{ CSortableObArray::SetAtGrow(nIndex, newElement); }
	int Add(TYPE newElement)
	{ return CSortableObArray::Add(newElement); }
	int Append(const CTypedPtrArray< CSortableObArray, TYPE >& src)
	{ return CSortableObArray::Append(src); }
	void Copy(const CTypedPtrArray< CSortableObArray, TYPE >& src)
	{ CSortableObArray::Copy(src); }
	
	// Operations that move elements around
	void InsertAt(int nIndex, TYPE newElement, int nCount = 1)
	{ CSortableObArray::InsertAt(nIndex, newElement, nCount); }
	void InsertAt(int nStartIndex, CTypedSortableObArray< TYPE >* pNewArray)
	{ CSortableObArray::InsertAt(nStartIndex, pNewArray); }
	
	// overloaded operator helpers
	TYPE operator[](int nIndex) const
	{ return (TYPE)CSortableObArray::operator[](nIndex); }
	TYPE& operator[](int nIndex)
	{ return (TYPE&)CSortableObArray::operator[](nIndex); }
	
	void Sort( int(*CompareFunc)(TYPE pFirstObj, TYPE pSecondObj) )
	{ CSortableObArray::Sort((int(*)(CObject*,CObject*))CompareFunc); }
	void Sort( int iStartPos, int iElements, int(*CompareFunc)(TYPE pFirstObj, TYPE pSecondObj) )
	{ CSortableObArray::Sort(iStartPos, iElements, (int(*)(CObject*,CObject*))CompareFunc); }
};



// SortableObArray.cpp
///////////////////////////////////////////////////////////////////

#define STRIDE_FACTOR 3

void CSortableObArray::Sort(int(*CompareFunc)(CObject* pFirst, CObject* pSecond))
{
	// CompareFunc is expected to return a positive integer if pFirstObj
	// should follow pSecondObj (is greater than)
	
	// Uses Shell Sort
	
	// Basically it does a bunch of smaller insertion sorts than insertion sorts the
	//  whole thing.  Insertion sorting is much faster on a list that is already
	//  mostly sorted.
	
	// ** NOTE:  Because GetSize() is called to retrieve the number of elements, you should
	//            call SetSize() with the number of valid elements.  An alternative is
	//            shown in the sort function below.
	
	ASSERT_VALID(this);
	
	BOOL bFound;
	int iElements = GetSize();
	int iInner,iOuter,iStride = 1;
	CObject *pTmp;
	
	while (iStride <= iElements)
		iStride = iStride * STRIDE_FACTOR + 1;
	
	while (iStride > (STRIDE_FACTOR - 1))
	{
		iStride = iStride / STRIDE_FACTOR;
		for (iOuter = iStride; iOuter < iElements; iOuter++)
		{
			bFound = 0;
			iInner = iOuter - iStride;
			while ((iInner >= 0) && !bFound)
			{
				if (CompareFunc(m_pData[iInner+iStride],m_pData[iInner]) < 0)
				{
					pTmp = m_pData[iInner+iStride];
					m_pData[iInner+iStride] = m_pData[iInner];
					m_pData[iInner] = pTmp;
					iInner -= iStride;
				}
				else
					bFound = 1;
			}
		}
	}
}

void CSortableObArray::Sort(int iStartPos, int iElements, int(*CompareFunc)(CObject* pFirst, CObject* pSecond))
{
	// This variation allows you to sort only a portion of the array
	
	ASSERT_VALID(this);
	ASSERT( iStartPos >= 0 && iStartPos <= GetUpperBound() );
	ASSERT( GetSize() - iStartPos >= iElements );
	
	BOOL bFound;
	int iInner,iOuter,iStride = 1;
	CObject *pTmp;
	CObject **pData = &m_pData[iStartPos];
	
	while (iStride <= iElements)
		iStride = iStride * STRIDE_FACTOR + 1;
	
	while (iStride > (STRIDE_FACTOR - 1))
	{
		iStride = iStride / STRIDE_FACTOR;
		for (iOuter = iStride; iOuter < iElements; iOuter++)
		{
			bFound = 0;
			iInner = iOuter - iStride;
			while ((iInner >= 0) && !bFound)
			{
				if (CompareFunc(pData[iInner+iStride],pData[iInner]) < 0)
				{
					pTmp = pData[iInner+iStride];
					pData[iInner+iStride] = pData[iInner];
					pData[iInner] = pTmp;
					iInner -= iStride;
				}
				else
					bFound = 1;
			}
		}
	}
}



// Usage
//////////////////////////////////////////////////////////

// Create a CObject based class
class CMyObject : public CObject
{
public:
    CString name;
    static int CompBackward(CMyObject* pFirstObj, CMyObject* pSecondObj)
    {
        return -lstrcmp((LPCTSTR)pFirstObj->name,(LPCTSTR)pSecondObj->name);
    }
};

// Create an array object
CTypedSortableObArray< CMyObject* > array;

array.SetSize(10);

// Fill the array with a bunch of objects
for (int i=0; i < 10; i++)
{
	CMyObject * pObj = new CMyObject;
	pObj->name.Format("Object #%d",i);
	array[i] = pObj;
}

// Sort the array
array.Sort(CMyObject::CompBackward);

// Display the contents of the now sorted array
for (int i=0; i < 10; i++)
{
	TRACE1("%s\n",array[i]->name);
}

Comments:

• Excellent! A couple compile tips for potential users... - David Emery (2000/04/18)
• What is shell sort? - Arnt Witteveen (2000/04/03)
• Great - Joe Bernier (2000/03/29)
• This class is great!!! - Olafur Bergsson (1999/07/27)
• There's a problem with the documentation of CompareFunc - Paul Hanley (1999/04/29)

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