Accessing a static Db object

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:

Quote:

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

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How can I solve this problem?

My db header:

Code:

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#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);
};

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Trying to call it from this class:

Code:

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

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And implementation:

Code:

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

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Thanks in advance

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.

Code:

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static Database* const  dbObj;

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Here is a short example that demonstrates the principle.

Code:

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#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;
}

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