Invalid conversion from and to void * when using ibpp in c++

Question

One of my class members has void * type:

void * conn;

In Connection method I set connection to Firebird database and set conn member like this:

IBPP::Database conn = IBPP::DatabaseFactory(host, dbname, user, pass);
conn->Connect();
this->conn = static_cast<void *>(conn);

This way of doing things works well for other multiple databases, but breaks when I try to use it with Firebird. So, this is what happens. In another method I use conn member to fetch data from a particular database. When it comes to Firebird, I do it like this:

IBPP::Transaction tr = IBPP::TransactionFactory(static_cast<IBPP::Database>(this->conn));

However, this line of code results in an error message:

error: invalid conversion from 'void *' to 'IBPP::IDatabase *'

I do not know what I'm doing wrong.

EDIT

Here are some code snippets from ibpp.h:

...
class IDatabase;
typedef Ptr<IDatabase> Database;
...
class IDatabase{
    public:
        virtual const char * ServerName() const = 0;
        virtual const char * DatabaseName() const = 0;
        ...
        virtual void Connect() = 0;
        ...
}

EDIT

Here is a reproducible testcase:

#define IBPP_LINUX
#include <ibpp.h>

int main(){
    //#1. No errors
    IBPP::Database conn = IBPP::DatabaseFactory("localhost","/var/lib/firebird/2.5/data/reestr.fdb","SYSDBA","root");
    conn->Connect();
    conn->Disconnect();
    //end of #1.
    //#2. Here we get errors.
    void * cn;
    IBPP::Database conn2 = IBPP::DatabaseFactory("localhost","/var/lib/firebird/2.5/data/reestr.fdb","SYSDBA","root");
    conn2->Connect();
    cn = static_cast<void *>(conn2);
    conn2->Disconnect();
    return 0;
}

and this is the error message, that I get when I try to compile it:

error: invalid static_cast from type IBPP::Database 
{aka IBPP::Ptr<IBPP::IDatabase>} to type void *

The error message points to this line of code:

cn = static_cast<void *>(conn2);

Answer 1

In a comment you say:

well, guys, please, pay attention to the fact that IBPP::Database is a typedef of IBPP::IDatabase *

No it isn't.

Look again:

error: invalid static_cast from type IBPP::Database
{aka IBPP::Ptr<IBPP::IDatabase>}

It's a typedef for Ptr<IDatabase>, not IDatabase*, so it is a smart pointer, and not convertible to void*

See http://www.ibpp.org/reference/guidelines#ibpp_smart_pointers_reference