Structure Question.

Hello, im new with Object oriented programming.
I'm having a problem with a structure, what I'm trying to do is to make a function to create a sub structure named depending on what the input is, let me show what ive done.

Code:

---

items.h

struct Weapon
{
    // Strings
    string mName;
    string mQuality;
   
    // Integers
    int mItemID;
    int mGoldValue;
    int mDamageLow;
    int mDamageHigh;
};

items.cpp

void Create(string name, string qual, int ID, int value, int dmgLow, int dmgHigh)
{
    Weapon name;
   
    name.mName = name;
    name.mQuality = qual;
    name.mItemID = ID;
    name.mGoldValue = value;
    name.mDamageLow = dmgLow;
    name.mDamageHigh = dmgHigh;
}

---

Now, I get an error that says: (declaration of 'Weapon name' shadows a parameter ).

Obviously I'm doing something wrong since im trying to make the parameter "name" be the name of the sub structure, for example: if user puts in "ShortSword" the name of it should be
"ShortSword.mName", and so on...

So is there any easier (working?) way to do this?

Thanks in advance.

In your main function, you have both a string and a 'Weapon' object with the same identifier, 'name'

I believe that you need to use this syntax:

Code:

---

struct Weapon name;

---

instead of

Code:

---

Weapon name;

---

EDIT and probably also change the name of your Weapon to something as per Etherous.

Duplicate variable names will cause quite a row with your compiler spitting all sorts of
related and seemingly non-related error messages.

Another point is that you can both create a constructor for your struct and change your syntax to support a more simple variable declaration:

Code:

---

typedef struct Weapon {
//...your stuff
} WEAPON, *PWEAPON;

---

then you can declare as such:

Code:

---

WEAPON myweapon;

---

Might be more convenient in the long run to just do this:

Code:

---

typedef struct Weapon
{
...
} Weapon;

---

Edit: ahoodin was faster

I believe that I mentioned that, although if you are referring to the use of capital letters, that appears to be the standard in books regarding the usage of typedef.

Quote:

---

Originally Posted by ahoodin

I believe that I mentioned that, although if you are referring to the use of capital letters, that appears to be the standard in books regarding the usage of typedef.

---

Sorry. You must have posted yours before I'd posted mine saying the same thing

The really odd thing about all this is that I believe we appear to be posting at precisely the same errr:ehh:....minute...lol I would not say second because it is not that precise.

I feel like Kreyton the robot from Red Dwarf, my favorite tv show

http://watchreddwarf.com/category/se...dwarf-season-1

All the stuff about needing "struct" in the type and the typedefs to get around it and whatnot.....doesn't apply to C++. Only C. And since this struct contains a std::string, there's no chance of using it in a C program anyway.

Thanks for all the answers!

I changed it some now, but ran into another problem.

Heres the new code:

items.h

Code:

---

#ifndef ITEMS_H
#define ITEMS_H

#include <string>
using namespace std;

struct Weapon
{
    void Create(string name, string qual, int ID, int value, int dmgLow, int dmgHigh);

    // Strings
    string mName;
    string mQuality;
   
    // Integers
    int mItemID;
    int mGoldValue;
    int mDamageLow;
    int mDamageHigh;
};

#endif

---

items.cpp

Code:

---

#include "items.h"
#include <string>

using namespace std;

void Weapon::Create(string name, string qual, int ID, int value, int dmgLow, int dmgHigh)
{
    mName = name;
    mQuality = qual;
    mItemID = ID;
    mGoldValue = value;
    mDamageLow = dmgLow;
    mDamageHigh = dmgHigh;
}

---

game.cpp

Code:

---

#include <iostream>
#include <cstdlib>
#include <ctime>
#include <string>

#include "items.h"

using namespace std;

int Init()
{
    Weapon ShortSword;
    ShortSword.Create("Short Sword", "Common", 1, 10, 1, 4);
}

int main()
{
    srand(time(0));
    Init();
   
    cout << ShortSword.mName << endl;
    system("pause");
    return 0;
}

---

But now i get these errors:

E:\Program\C++ Game Programming Files\Quillon\game.cpp In function `int main()':
22 E:\Program\C++ Game Programming Files\Quillon\game.cpp `ShortSword' undeclared (first use this function)
(Each undeclared identifier is reported only once for each function it appears in.)
E:\Program\C++ Game Programming Files\Quillon\Makefile.win [Build Error] [game.o] Error 1


Any suggestions?

Well at this point it appears to be a problem with your scope. Your ShortSword variable only has local scope to Init(). It needs to be upgraded to either class scope, or declared in main.

Quote:

---

Obviously I'm doing something wrong since im trying to make the parameter "name" be the name of the sub structure, for example: if user puts in "ShortSword" the name of it should be
"ShortSword.mName", and so on...

---

What you want isn't possible in C++. Understand, the identifiers in your code "Weapon", "name", "mQuality", or whatever, don't even exist when the program runs. They are just used to make it easy for us lowly humans to read and understand code.

If you want to identify something by a user defined name, you give it a string attribute to hold that name. Which you've already done. Or, depending on exactly what your needs are, you may to look at std::map.

I understood him quite well. As for being a lowly human, that is a career choice.
(so I assume you speak for yourself)

So i need to make it into a class or declare in main?

If i made, lets say 100 different Weapons, it would be a little too much code that goes into main, so isnt there any other way to make it into a function to make it look cleaner in main?

It sounds to me like you want a std::map< std::string, Weapon >. That's the closest you can get to what you seem to be trying to do.

Alternatively, you could look into inheritance, for instance defining ShortSword as a subclass of Weapon. That wouldn't be worthwhile unless you had a number of different ShortSword objects you expected to be manipulating with various properties.

From your questions, I'm wondering whether you really understand what object scope is all about.

Quote:

---

Originally Posted by Lindley

It sounds to me like you want a std::map< std::string, Weapon >. That's the closest you can get to what you seem to be trying to do.

Alternatively, you could look into inheritance, for instance defining ShortSword as a subclass of Weapon. That wouldn't be worthwhile unless you had a number of different ShortSword objects you expected to be manipulating with various properties.

From your questions, I'm wondering whether you really understand what object scope is all about.

---

No Im not sure, I've just started to learn C++ and its not in the book I have (Game Institute, Game Programming 1).

But could you give me a link to an explanation / example?

Hm, now I just changed some code and it works.

Earlier:

Code:

---

#include <iostream>
#include <cstdlib>
#include <ctime>
#include <string>

#include "items.h"

using namespace std;

int Init()
{
    Weapon ShortSword;
    ShortSword.Create("Short Sword", "Common", 1, 10, 1, 4);
}

int main()
{
    srand(time(0));
    Init();
   
    cout << ShortSword.mName;
    system("pause");
    return 0;
}

---

Changed To:

Code:

---

#include <iostream>
#include <cstdlib>
#include <ctime>
#include <string>

#include "items.h"

using namespace std;

int main()
{
    srand(time(0));
   
    Weapon ShortSword;
    ShortSword.Create("Short Sword", "Common", 1, 10, 1, 4);
   
    cout << ShortSword.mName;
   
    system("pause");
    return 0;
}

---

So basically all I did was to create the structure in main, instead of in a function with the creation that is called in main.

Can someone explain why it works to create it in main, but not in a function which is called in main?

Thanks.

Quote:

---

Originally Posted by ahoodin

I understood him quite well.

---

Apparently not, since it took 12 posts for someone to address what he was actually wanting to do.

Quote:

---

As for being a lowly human, that is a career choice.
(so I assume you speak for yourself)

---

Unless you happen to be fluent in machine code, you're a lowly human in this context.

Quote:

---

Can someone explain why it works to create it in main, but not in a function which is called in main?

---

http://en.wikipedia.org/wiki/Scope_(programming)
http://en.wikipedia.org/wiki/Variabl...ope_and_extent

If the book you're learning from has gotten you into functions and structures without explaining something as basic as scope, I'd really suggest looking for another book.

I do understand scopes, but what im asking is: do you have to create structures in main like this:

Code:

---

int main()
{
    Weapon sword;
    Weapon dagger;
    Weapon axe;
    Weapon bow;
}

---

And is it impossible to create them in void functions which is called in main when to create them?

Code:

---

void Call();

int main()
{
  Call();
}

void Call()
{
    Weapon sword;
    Weapon dagger;
    Weapon axe;
    Weapon bow;
}

---

Its hard to explain it when everyone is thinking so complex.

Code:

---

void Call( )
{
  Weapon sword;
  Weapon dagger;
  Weapon axe;
  Weapon bow;
} // <-- sword, dagger, axe and bow go out of scope at this point, and no longer exist

---

There are various methods to have a function create objects that are useable after that function ends. Namely, have the function take some STL container by reference and insert the objects into that container.

Simple example using a map:

Code:

---

typedef std::map<std::string, Weapon> WeaponMap;

void Create(WeaponMap& wm)
{
  wm["sword"] = Weapon(/*params*/);
  wm["dagger"] = Weapon(/*params*/);
  // etc
}

int main( )
{
  WeaponMap weps;
 
  Create(weps);
 
  cout << weps["sword"].mName;
 
  return 0;
}

---

I think I understand how it works now, thanks mate.

Quote:

---

Originally Posted by Speedo

Unless you happen to be fluent in machine code, you're a lowly human in this context.

---

I'm afraid I don't care for the context. Speak for yourself mate.

Quote:

---

Originally Posted by Speedo

Apparently not, since it took 12 posts for someone to address what he was actually wanting to do.

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Well again I am afraid this is a matter of opinion.