CString used on static method - c++

Question

I am stuck into a problem, and I will be very grateful if you help me.
I have a MDI, and in CDocument class, I have a struct:
CMyDoc.h
class CMyDoc : public CDocument
{
...
struct SRecord
{
SRecord(){}
virtual ~SRecord(){}
CString sName;
CString sState;
CString sDateu;
CString sDatec;
};
CTypedPtrArray<CPtrArray, SRecord*> m_arrRecord;
and somewhere I load this struct with data:
SRecord* pItem = new SRecord;
pItem->sName = saItem.GetAt(ML_ASSETNAME);
pItem->sState = saItem.GetAt(ML_STATE);
pItem->sDateu = saItem.GetAt(ML_DATEU;
pItem->sDatec = saItem.GetAt(ML_DATEC);
m_arrRecord.Add(pItem);
ok. I am trying to sort data:
void CMyDoc::SortData(int nColumn, BOOL bAscending)
{
switch(nColumn)
{
case 9:
if(bAscending)qsort((void*)m_arrRecord.GetData(), m_arrRecord.GetSize(), sizeof(SRecord), CompareDateUAscending);
else qsort((void*)m_arrRecord.GetData(), m_arrRecord.GetSize(), sizeof(SRecord), CompareDateUDescending);
break;
...
}
but the problem become when data is access in static method:
int CMyDoc::CompareDateUDescending(const void* arg1, const void* arg2)
{
SRecord* Record1 = (SRecord*)arg1;
SRecord* Record2 = (SRecord*)arg2;
if(Record1->sDateu.IsEmpty() || Record2->sDateu.IsEmpty()) // <--- crash !
return 0;
COleDateTime dL, dR;
dL.ParseDateTime(Record1->sDateu);
dR.ParseDateTime(Record2->sDateu);
return (dL == dR ? 0 : (dL < dR ? 1 : -1));
}
and the crash take me here (atlsimpstr.h):
CStringData* GetData() const throw()
{
return( reinterpret_cast< CStringData* >( m_pszData )-1 ); // the crash lead me on this line
}
what I am doing wrong ?
Any help will be very appreciated !
Update:
I have tried this:
int CMyDoc::CompareDateUDescending(const void* arg1, const void* arg2)
{
SRecord* Record1 = *(SRecord**)arg1; // <-- OK
SRecord* Record2 = *(SRecord**)arg2; // <-- Unhandled exception* see note below
if(Record1->sDateu.IsEmpty() || Record2->sDateu.IsEmpty())
return 0;
COleDateTime dL, dR;
dL.ParseDateTime(Record1->sDateu);
dR.ParseDateTime(Record2->sDateu);
return (dL == dR ? 0 : (dL < dR ? 1 : -1));
}
and the crash told me:
"An unhandled exception was encountered during a user callback." strange ...

Answer 1

The qsort comparison function receives pointers to the elements in the array. But since the elements in the array are themselves pointers what your specific function receives as arguments are pointers to pointers to SRecord, i.e. SRecord**.
You can solve it by doing e.g.
const SRecord* Record1 = *reinterpret_cast<const SRecord**>(arg1);
That is, you cast arg1 to SRecord** and then dereference that pointer to get a SRecord*.
Example on how to use the C++ standard sort function.
First you need to update your comparison function a little:
// The comparison function should return true if Record1 is *smaller* than Record2,
// and return false otherwise
bool CMyDoc::CompareDateUDescending(const SRecord* Record1, const SRecord* Record2)
{
return Record1->sDateu < Record2->sDateu;
}
Then to call sort:
std::sort(m_arrRecord.GetData(), m_arrRecord.GetData() + m_arrRecord.GetSize(), CompareDateUDescending);
Much simpler!