ctor/dtor problem
 

So in my class we just finished covering the topic of constructors and destructors. Now, my teacher has given us a lab where we have to create these classes and each of them must have a ctor/dtor. The problem I'm running into is..well.. it would be easier to describe in code :mrgreen:

here's what my main looks like:

class Database

{

public:

        Database(char * file = "states.txt");

        ~Database(void);

        void deleteDatabase ();

        void fillDatabase ();

        void insertDatabase (int index, State & tempState);

        void printDatabase ();

private:

        State * list;                // array of states

        int count;                        // total count of states

        char * filename;        // input filename

};

class State

{

public:

        State::State();

//        State::State(char * name, int year, char * cap, int popRank);

        State::~State();

        void initState(char * tempName, int tempYear, char * tempCap, int tempPopRank);

        void copyState(State & tempState);

        void printState();

private:

        char * name;        // state name

        int year;                // year of entry into the union

        char * cap;                // state capital

        int popRank;        // population ranking

};

int main(void)

{



        Database db;

        

        db.fillDatabase();

        db.printDatabase();



        return 0;

}

and here's the fillDatabase function:

void Database::fillDatabase ()

{

        char name[80];        // temp variables

        int year;                // to store

        char cap[80];        // input data

        int popRank;                // from file

        int index = 0;        // index into array of State structs

        char array[100]; // temporary storage for file input

        State tempState;



        // open file from filename field of db

        // don't need to check for file open success because initDatabase already checked

        ifstream inputFile( filename );

        

        // loop through all the states

        for ( int cnt = 0; cnt < count; cnt++ )

        {

            // read and parse one line of file into 4 input data fields

                if ( !inputFile.eof() )

                {

                        inputFile.getline( array, 100 );



                        if ( sscanf( array, "%[^,], %d, %[^,], %d",        name, &year, cap, 

                                &popRank ) == 4 )

                        {

                                // if tempState is created successfully from the 4 input data

//                                State tempState( name, year, cap, popRank );

                                tempState.initState(name, year, cap, popRank);

                                insertDatabase (index, tempState);

                        }

                        else

                        {

                                cout << "Error with file!" << '\n';

                                return;

                        }

                        index++;

                }

        }

 

         // close file

         inputFile.close();

}

void Database::insertDatabase (int index, State & tempState)

{

   // set pCurrent to location to be inserted in array

        State * pCurrent = list + index;

        // copy from state to pCurrent

        pCurrent->copyState( tempState );

        

        return;

}

In this function i'm creating an instance of the tempState class to temporarily store data from the file and then copy the data into the db instance. The problem is that as soon as I leave this function, the destructor is invoked and deletes the last piece of data that the list was pointing to. How would I circumvent this problem (other than not creating a destructor)?

Re: ctor/dtor problem
 

1. The problem is that, just like all other objects, tempState is destroyed when it goes out of scope and fillDatabase() runction returns to whoever called it. If you do not expicitely code the destructor c++ will write one for you.

Why do you want tempState to live outside the function in which it is defined? If it is necessary, then I would either (1) add it as a member object of the class, or (2) pass a reference to the object as a parameter to fillDatabase().

Re: ctor/dtor problem
 

well thanks for the reply. I think I figured out the problem over lunch lol.