Accessing a static Db object

[olamalam]

Dear All,

I've created a database class in my project and I'm opening a db connection with that class whenever I need to query Db. However, it's very inefficient creata new database object in every function call and open a connection to database. For that reason I'm trying to change my implementation and create a static protected db object and open a connection once and close it when I finish all my queries.

So far, it sounds reasonable and easy

However, when I call "open" method of my database class from another class, I'm getting this error:

error C2662: 'Database::Open' : cannot convert 'this' pointer from 'const Database' to 'Database &'

How can I solve this problem?

My db header:

#define CATCHERROR(ptr,a)	catch(_com_error &e)\
							{\
								ErrorHandler(e,m_ErrStr);\
								ptr=NULL;\
								return a;\
							}

#define CATCHERRGET			catch(_com_error &e)\
							{\
								ErrorHandler(e,m_ErrStr);\
								sprintf(m_ErrStr,"%s\n**For Field Name:%s",m_ErrStr,FieldName);\
								return 0;\
							}

#import "c:\Program Files\Common Files\System\ADO\msado15.dll" \
              rename("EOF", "EndOfFile")

typedef ADODB::_RecordsetPtr	RecPtr;
typedef ADODB::_ConnectionPtr	CnnPtr; 

class Database;
class Table;


class Database
{
public:
	CnnPtr m_Cnn;
	char m_ErrStr[500];
	Database();
	bool Open(char* UserName, char* Pwd,char* CnnStr);
	bool Close();
	bool OpenTbl(int Mode, char* CmdStr, Table& Tbl);
	bool Execute(const char* CmdStr);
	bool Execute(const char* CmdStr, Table& Tbl);
	void GetErrorErrStr(char* ErrStr);
};

class Table{
public:
	RecPtr m_Rec;
	char m_ErrStr[500];
	Table();
	void GetErrorErrStr(char* ErrStr);
	int ISEOF();
	HRESULT MoveNext();
	HRESULT MovePrevious();
	HRESULT MoveFirst();
	HRESULT MoveLast();
	int AddNew();
	int Update();
	int Add(char* FieldName, char* FieldValue);
	int Add(char* FieldName,int FieldValue);
	int Add(char* FieldName,float FieldValue);
	int Add(char* FieldName,double FieldValue);
	int Add(char* FieldName,long FieldValue);
	bool Get(char* FieldName, char* FieldValue);
	bool Get(char* FieldName, std::string& FieldValue);	
	int GetInt(char* FieldName);
	bool Get(char* FieldName,float& FieldValue);
	bool Get(char* FieldName,double& FieldValue);
	bool Get(char* FieldName,double& FieldValue,int Scale);
	bool Get(char* FieldName,long& FieldValue);
};

Trying to call it from this class:

#include "Database.h"
namespace Myclass
{
    class Myclass
    {	
	protected:
		static const Database* dbObj;
}
}

And implementation:

if(!dbObj->Open(userIdValue, passwordValue, CnnStr)){}

Thanks in advance

[kempofighter]

You are trying to call a non-const function of the class via a pointer to a const object. The open function is not a const function. Do you need the database pointer to be declared as a pointer to a const object? You probably just wanted the pointer to be const, not the object itself.

Try this.

static Database* const  dbObj;

Here is a short example that demonstrates the principle.

#include <iostream>

class ConstPointerOrConstData
{
public:
    ConstPointerOrConstData(int i) : i(i) {}
    void print() { std::cout << i << std::endl; }

private:
    int i;
};

int main(int argc, char *argv[])
{
    ConstPointerOrConstData value(5);
    const ConstPointerOrConstData* valuePtrToConst = &value;
    ConstPointerOrConstData* const constPtrToValue = &value;

    constPtrToValue->print();
    valuePtrToConst->print();
    
    return 0;
}