Parlando di VC6, quando si lancia un puntatore di una classe (che si crea un'istanza) in una variabile (ad es. DWORD), anche se questo puntatore è locale è possibile accedere alla classe su tutte le funzioni che utilizzano lo stesso heap. La classe istanziata è definita come locale ma in realtà non lo è. Per quanto ne so, qualsiasi indirizzo di una variabile, struttura o classe di heap è unico per tutta la vita della classe di hosting.
Esempio:
class MyClass1 {
public:
void A (void);
void B (void);
void C (void);
private:
DWORD dwclass;
};
class MyClass2 {
public:
int C (int i);
};
void MyClass1::A (void) {
MyClass2 *myclass= new MyClass2;
dwclass=(DWORD)myclass;
}
void MyClass1::B (void) {
MyClass2 *myclass= (MyClass2 *)dwclass;
int i = myclass->C(0); // or int i=((MyClass2 *)dwclass)->C(0);
}
void MyClass1::B (void) {
MyClass2 *myclass= (MyClass2 *)dwclass;
delete myclass;
}
EDIT Questa è una parte molto piccola del codice originale. La classe CSRecodset è solo una classe di casting di CXdbRecordset, dove si trova tutto il codice reale. In questo modo posso consentire all'utente di trarre vantaggio da ciò che ho scritto senza perdere i miei diritti. Non pretendo di dimostrare che il mio motore di database è professionale ma funziona davvero.
//-------------------------------------
class CSRecordSet : public CSObject
//-------------------------------------
{
public:
CSRecordSet();
virtual ~CSRecordSet();
// Constructor
bool Create(CSDataBase* pDataBase,CSQueryDef* pQueryDef);
//Open, find, close
int OpenRst(bool bReadBlanks=0,bool bCheckLastSql=0,bool bForceLoad=0,bool bMessage=1); // for a given SQL
int FindRecord(bool bNext); // for a given SQL
// TABLE must be ordered by the same fields that will be seek
bool SeekRecord(int nFieldIndex, char *key, int length=0); // CRT bsearch
bool SeekRecord(int nFieldIndex, long key);
bool SeekRecord(int nFieldIndex, double key, int decimals);
bool SeekRecord(XSEK *SEK);
bool DeleteRecord(void);
bool Close(void);
// Record Position:
bool IsEOF(void); // pointer out of bound
bool IsLAST(void); // TRUE if last record
bool IsBOF(void); // pointer out of bound
bool IsOpen(void);
bool Move(long lRows); // returns FALSE if out of bound
void MoveNextNotEof(void); // eof is tested
void MoveNext(void); // eof is not tested
void MovePrev(void); // bof is tested
void MoveLast(void);
void MoveFirst(void);
void SetAbsolutePosition(long lRows);
long GetAbsolutePosition(void);
void GoToLast(void); // Restore position after a Filter
// Table info
long GetRecordCount(void);
int GetRstTableNumber(void);
int GetRecordLength(void); //includes stamp (sizeof char)
int GetTableType(void);
// Field info
int GetFieldCount(void);
void GetFieldName(int nFieldIndex, char *pbuffer);
int GetFieldIndex(const char *sFieldName);
int GetFieldSize(int nFieldIndex);
int GetFieldDGSize(int nFieldIndex); // String size (i.e. dg_Boolean)
long GetRecordID(void);
int GetStandardFieldCount(void);
bool IsMemoFileTable(void);
bool IsNumberField(int nFieldIndex);
int GetFieldType(int nFieldIndex);
// Read Field value
bool GetFieldValue(int nFieldIndex, XdbVar& var);
bool GetFieldValueIntoBuffer(int nFieldIndex,char *pbuffer);
char *GetMemoField(int nMemoFieldIndex, char *pbuffer, int buf_size);
bool GetBinaryField(unsigned char *buffer,long *buf_size);
// Write Field value
void Edit(void); // required
bool SetFieldValue(int nFieldIndex, XdbVar& var);
bool SetFieldValueFromBuffer(int nFieldIndex,const char *pbuffer);
bool Update(void); // required
// pointer to the same lpSql
LPXSQL GetSQL(void);
};
//---------------------------------------------------
CSRecordSet::CSRecordSet(){
//---------------------------------------------------
pClass |= (CS_bAttach);
}
CSRecordSet::~CSRecordSet(){
if(pObject) delete (CXdbRecordset*)pObject;
}
bool CSRecordSet::Create(CSDataBase* pDataBase,CSQueryDef* pQueryDef){
CXdbQueryDef *qr=(CXdbQueryDef*)pQueryDef->GetObject();
CXdbTables *db=(CXdbTables*)pDataBase->GetObject();
CXdbRecordset *rst = new CXdbRecordset(db,qr);
if(rst==NULL) return 0;
pObject = (unsigned long) rst;
return 1;
}
bool CSRecordSet::Close(void){
return ((CXdbRecordset*)pObject)->Close();
}
int CSRecordSet::OpenRst(bool bReadBlanks,bool bCheckLastSql,bool bForceLoad, bool bMessage){
unsigned long dw=0L;
if(bReadBlanks) dw|=SQL_bReadBlanks;
if(bCheckLastSql) dw|=SQL_bCheckLastSql;
if(bMessage) dw|=SQL_bRstMessage;
if(bForceLoad) dw|=SQL_bForceLoad;
return ((CXdbRecordset*)pObject)->OpenEx(dw);
}
int CSRecordSet::FindRecord(bool bNext){
return ((CXdbRecordset*)pObject)->FindRecordEx(bNext);
}
bool CSRecordSet::DeleteRecord(void){
return ((CXdbRecordset*)pObject)->DeleteEx();
}
bool CSRecordSet::IsEOF(void){
return ((CXdbRecordset*)pObject)->IsEOF();
}
bool CSRecordSet::IsLAST(void){
return ((CXdbRecordset*)pObject)->IsLAST();
}
bool CSRecordSet::IsBOF(void){
return ((CXdbRecordset*)pObject)->IsBOF();
}
bool CSRecordSet::IsOpen(void){
return ((CXdbRecordset*)pObject)->IsOpen();
}
bool CSRecordSet::Move(long lRows){
return ((CXdbRecordset*)pObject)->MoveEx(lRows);
}
void CSRecordSet::MoveNextNotEof(void){
((CXdbRecordset*)pObject)->MoveNextNotEof();
}
void CSRecordSet::MoveNext(void){
((CXdbRecordset*)pObject)->MoveNext();
}
void CSRecordSet::MovePrev(void){
((CXdbRecordset*)pObject)->MovePrev();
}
void CSRecordSet::MoveLast(void){
((CXdbRecordset*)pObject)->MoveLast();
}
void CSRecordSet::MoveFirst(void){
((CXdbRecordset*)pObject)->MoveFirst();
}
void CSRecordSet::SetAbsolutePosition(long lRows){
((CXdbRecordset*)pObject)->SetAbsolutePosition(lRows);
}
long CSRecordSet::GetAbsolutePosition(void){
return ((CXdbRecordset*)pObject)->m_AbsolutePosition;
}
long CSRecordSet::GetRecordCount(void){
return ((CXdbRecordset*)pObject)->GetRecordCount();
}
int CSRecordSet::GetFieldCount(void){
return ((CXdbRecordset*)pObject)->GetFieldCount();
}
int CSRecordSet::GetRstTableNumber(void){
return ((CXdbRecordset*)pObject)->GetRstTableNumber();
}
void CSRecordSet::GetFieldName(int nFieldIndex, char *pbuffer){
((CXdbRecordset*)pObject)->GetFieldName(nFieldIndex,pbuffer);
}
int CSRecordSet::GetFieldIndex(const char *sFieldName){
return ((CXdbRecordset*)pObject)->GetFieldIndex(sFieldName);
}
bool CSRecordSet::IsMemoFileTable(void){
return ((CXdbRecordset*)pObject)->IsMemoFileTable();
}
bool CSRecordSet::IsNumberField(int nFieldIndex){
return ((CXdbRecordset*)pObject)->IsNumberField(nFieldIndex);
}
bool CSRecordSet::GetFieldValueIntoBuffer(int nFieldIndex,char *pbuffer){
return ((CXdbRecordset*)pObject)->GetFieldValueIntoBuffer(nFieldIndex,pbuffer);
}
void CSRecordSet::Edit(void){
((CXdbRecordset*)pObject)->Edit();
}
bool CSRecordSet::Update(void){
return ((CXdbRecordset*)pObject)->Update();
}
bool CSRecordSet::SetFieldValue(int nFieldIndex, XdbVar& var){
return ((CXdbRecordset*)pObject)->SetFieldValue(nFieldIndex,var);
}
bool CSRecordSet::SetFieldValueFromBuffer(int nFieldIndex,const char *pbuffer){
return ((CXdbRecordset*)pObject)->SetFieldValueFromBuffer(nFieldIndex,pbuffer);
}
bool CSRecordSet::GetFieldValue(int nFieldIndex, XdbVar& var){
return ((CXdbRecordset*)pObject)->GetFieldValue(nFieldIndex,var);
}
bool CSRecordSet::SeekRecord(XSEK *SEK){
return ((CXdbRecordset*)pObject)->TableSeek(SEK);
}
bool CSRecordSet::SeekRecord(int nFieldIndex,char *key, int length){
return ((CXdbRecordset*)pObject)->TableSeek(nFieldIndex,key,length);
}
bool CSRecordSet::SeekRecord(int nFieldIndex,long i){
return ((CXdbRecordset*)pObject)->TableSeek(nFieldIndex,i);
}
bool CSRecordSet::SeekRecord(int nFieldIndex, double d, int decimals)
{
return ((CXdbRecordset*)pObject)->TableSeek(nFieldIndex,d,decimals);
}
int CSRecordSet::GetRecordLength(void){
return ((CXdbRecordset*)pObject)->GetRecordLength();
}
char *CSRecordSet::GetMemoField(int nMemoFieldIndex,char *pbuffer, int BUFFER_SIZE){
return ((CXdbRecordset*)pObject)->GetMemoField(nMemoFieldIndex,pbuffer,BUFFER_SIZE);
}
bool CSRecordSet::GetBinaryField(unsigned char *buffer,long *buf_size){
return ((CXdbRecordset*)pObject)->GetBinaryField(buffer,buf_size);
}
LPXSQL CSRecordSet::GetSQL(void){
return ((CXdbRecordset*)pObject)->GetSQL();
}
void CSRecordSet::GoToLast(void){
((CXdbRecordset*)pObject)->GoToLast();
}
long CSRecordSet::GetRecordID(void){
return ((CXdbRecordset*)pObject)->GetRecordID();
}
int CSRecordSet::GetStandardFieldCount(void){
return ((CXdbRecordset*)pObject)->GetStandardFieldCount();
}
int CSRecordSet::GetTableType(void){
return ((CXdbRecordset*)pObject)->GetTableType();
}
int CSRecordSet::GetFieldType(int nFieldIndex){
return ((CXdbRecordset*)pObject)->GetFieldType(nFieldIndex);
}
int CSRecordSet::GetFieldDGSize(int nFieldIndex){
return ((CXdbRecordset*)pObject)->GetFieldDGSize(nFieldIndex);
}
int CSRecordSet::GetFieldSize(int nFieldIndex){
return ((CXdbRecordset*)pObject)->GetFieldSize(nFieldIndex);
}
EDIT: richiesto da DeadMG:
void nimportequoidumomentquecaroule(void) {
short i = -4;
unsigned short j=(unsigned short)i;
}