Default Constructors w/Classes as Parameters

Confusing title, confusing question.
First off, I'm making arrays of type Room (class). I'm aware I have to have default constructor arguments for this to work... or whatever you call it. My problem is, I can't seem to give a default value to one of the parameters in my constructor function; and that parameter type happens to be another class.

The constructor header:

Code:

---

Room::Room(int dr = 0, int dc = 0,                  // row, column number (d for default arguments)
          bool dN = true, bool dE = true,          // exits (N, E)
          bool dS = true, bool dW = true,          // exits (S, W)
          char* dname = '\0', char* ddescr = '\0',  // name, description
          Monster dmob)

---

Okay Dokay - since I am creating an array of these Room types, I need default constructor arguments.. and I have them there.. all except for the last parameter (Monster dmob). How can I give this a default value?

If this doesn't make sense please say so, and i'll post the rest of the code.

maybe you could use a pointer to a Monster object and make it NULL in the constructor?

hmm.. that sounds like it will work. but i dont know what any of that means... 'specially that null pointer (i a newb)
Could you explain in a nutshell what that is?
Is it something like this?

Code:

---

Room::Room(........,Monster* p_Monster = NULL)
{
 // ....
 thePrivateDataMemberOfTypeMonster = *p_Monster;
}

---

yup, that looks correct

Wow, thanks endo!!

Of course if you are making a default constructor, then you know you can just create one with no arguments right? eg

Code:

---

Room::Room( )
{
  dr = dc = 0;
  dN = dS = dW = dE = true;
  dname = ddesc = NULL;
  //no need to initialise Monster, its defualt constructor should do that
}

---

Anyway, its just another idea...

(kind off subject)
*Wants to be as smart as endo some day*
What book do you reccommend for beginners endo? That C++ 21 days seems popular...

I aint that smart, if I was I'd have a programming job :(

Anyway, I've got "C++ How to Program", third ed - Deitel & Deitel. Thats a good book which seemed really complex when I started but I don't think you'll struggle with it at all. It covers loads of stuff as well, still not read the whole book...

Edit : And it comes with the intro version of Visual C++ 6, which is nice.

Thankyou

Doh. It compiled just fine with no errors, but now when I try to run the .exe, i get illegal operation! *whine*

Is it definitly because of the constructor? post the code.

it is very big.
should i upload it or post it?

Okay here's the whole thing.

The classes are in classes.h

I have errors telling me there is no appropriate default constructor for Room and Monster Objects. I have removed your Monster constructor and put this instead, which doesn't produce errors

Code:

---

Monster::Monster( )
{
        maxHP = curHP = str = agi = gold = xp = 0;
        alive = false;
        name = art = Art = attack = dodge = NULL;
}

---

I can fix the whole lot if you like but the Room constructor is going to be very similar, so if this isn't what you want say so now.

For the Room class you will also need to overload the assignment(=) operator for the Monster class because you'll get dodgy results otherwise.

Sounds good to me! I'm always looking for pointers at c++ (not the pointers to addresses)

I'm not quite sure what overloaded assignment is.

You are awesome! I took out all the parameters for the default constructors for Room and Monster like you said -- works like a charm
you're good

The default Room constructor:

Code:

---

Room::Room( )
{
        r = c = 0;  //unsure about what this does so I'll just set it to 0
        N = E = S = W = false;
        name = descr = NULL;
}

---

Remember these create useless rooms, no names, descriptions, exits, monsters or anything. Same with the default Monster constructor.

Overloaded = operators are required so that you can do things like this safely:

Code:

---

Monster m1, m2;
m1.changeSomething( );
m2 = m1;  //= used here

---

Just working on a bit of the overloaded = then I'll post that :)

hermm.. try not to change TOO much to the point where it is unreadable by me, a n00b (see the avatar?). If you do change something, do you think you could explain? I just started C++ 3 weeks ago!.

OK but you will need it if you are going to use strings represented as char*'s. Here is part of the overloaded assignment, if its too complex say so and you should probably use string objects instead.

Code:

---

Monster& Monster::operator =( Monster&  rvalue )
{
        //routine assignent of values
        alive = rvalue.alive;
        maxHP = rvalue.maxHP;
        curHP = rvalue.curHP;
        str = rvalue.str;
        agi = rvalue.agi;
        gold = rvalue.gold;
        xp = rvalue.xp;

        //create space for name attribute
        name = new char[ strlen( rvalue.name )+1 ];
        if( name == NULL )
        {
                cout << "Insufficient memory, exiting....";
                exit( 0 );
        }
        else
        {
                strcpy( name, rvalue.name );  //copying name
        }
        return *this;
        //UNFINISHED
}

---

The compiler creates a default operator for your classes but that would just copy rvalue.name into name leaving 2 objects pointing at the same space to represent name. Therefore if you change 1 then the other would also change, not good.

By the way, your doing much better than I was after 3 weeks - I wasn't even on to pointers until week 4!

EEP - yes, that all looks very complex and the only part I understand is:

Quote:

---

Code:

---

cout << "Insufficient memory, exiting....";

---

---

I see you have *this pointer.. I can't get that far in my C++ book cause the author expects me to already understand everything.
& I'm hesitant to use the new[] thingy because I dont understand the benefits of it or what dynamic memory really is...

Since i'm too n00bish, i should use string types instead of char*?

you could do, but you could also use char arrays. Just declare name as char name[ 20 ] or something then treat them as char*'s after that. That way you will know exactly how much space you have every time.

or you could declare them as string objects, which takes care of most of that stuff for you.

string name;
string attack;
etc.
etc.

If you do that the set them to an empty string in the constructor:

name = "";

Hope that helps, the char arrays are more educational but string objects are simpler to use.

thanks for helping with those constructors - you saved me hours of pressing the re-build button.
i have no idea what i'm gonna do about those char*'s now though. I'd like to learn why I need all that overloaded operator stuff - but i'm too stupid to comprehend it =P.

Thanks again for spending the time to help!

No problem I remember how tough it is when you are starting. I'd suggest using string objects for now though, they are nice and versatile :)