To manage our database open and close activities, we encapsulate them in the MyDb class. There are several good reasons to do this, the most important being that we can ensure our databases are closed by putting that activity in the MyDb class destructor.

To begin, we create our class definition:

// File: MyDb.hpp
#include <db_cxx.h>

class MyDb
{
public:
    // Constructor requires a path to the database,
    // and a database name.
    MyDb(std::string &path, std::string &dbName);

    // Our destructor just calls our private close method.
    ~MyDb() { close(); }

    inline Db &getDb() {return db_;}

private:
    Db db_;
    std::string dbFileName_;
    u_int32_t cFlags_;

    // Make sure the default constructor is private
    // We don't want it used.
    MyDb() : db_(NULL, 0) {}

    // We put our database close activity here.
    // This is called from our destructor. In
    // a more complicated example, we might want
    // to make this method public, but a private
    // method is more appropriate for this example.
    void close();
}; 

Next we need the implementation for the constructor:

// File: MyDb.cpp
#include "MyDb.hpp"

// Class constructor. Requires a path to the location
// where the database is located, and a database name
MyDb::MyDb(std::string &path, std::string &dbName)
    : db_(NULL, 0),               // Instantiate Db object
      dbFileName_(path + dbName), // Database file name
      cFlags_(DB_CREATE)          // If the database doesn't yet exist,
                                  // allow it to be created.
{
    try
    {
        // Redirect debugging information to std::cerr
        db_.set_error_stream(&std::cerr);

        // Open the database
        db_.open(NULL, dbFileName_.c_str(), NULL, DB_BTREE, cFlags_, 0);
    }
    // DbException is not a subclass of std::exception, so we
    // need to catch them both.
    catch(DbException &e)
    {
        std::cerr << "Error opening database: " << dbFileName_ << "\n";
        std::cerr << e.what() << std::endl;
    }
    catch(std::exception &e)
    {
        std::cerr << "Error opening database: " << dbFileName_ << "\n";
        std::cerr << e.what() << std::endl;
    }
}

And then we need the implementation for the close() method:

// Private member used to close a database. Called from the class
// destructor.
void
MyDb::close()
{
    // Close the db
    try
    {
        db_.close(0);
        std::cout << "Database " << dbFileName_
                  << " is closed." << std::endl;
    }
    catch(DbException &e)
    {
        std::cerr << "Error closing database: " << dbFileName_ << "\n";
        std::cerr << e.what() << std::endl;
    }
    catch(std::exception &e)
    {
        std::cerr << "Error closing database: " << dbFileName_ << "\n";
        std::cerr << e.what() << std::endl;
    }
}