Copy Contruct and Value in Array Of Object

[shayankhan]

Hello guys i am in level of class and objects
i need some help and guide in copy contruct i search the thread
and found 1 http://www.daniweb.com/forums/thread21662.html
but this is not what i want... ok here is the problem..

i created contruct class ... i want in program that create objects
on user input.. like how many computer you need.. if user enter 5
then compiler create 5 objects of class computer.. after that it asks
for computer specification and compiler then copy some contents to other
4 objects ... i coded the program it works perfect but the copy method copies
every contents of 1st object into others.. how can i copy some contents ..
this scenario is done with array object. please guide me if there is any better idea.

#include "iostream"
#include "string"
using namespace std;
class cmptr
{
private:
	string rm;
	string hd;
	string nme;
	string agp;
	string mothrbrd;
	int lcd;
	int pcr;
public:
	void defaultinfo()
	{
		cout<<"PC SPEC ";
		cout<<"Enter pc name: ";
		cin>>name;
		cout<<"Enter processor speed: ";
		cin>>pcr;
		cout<<"Enter ram size: ";
		cin>>ram;
		cout<<"Enter motherboard model: ";
		cin>>mothrbrd;
		cout<<"Enter graphics card size: ";
		cin>>agp;
		cout<<"Enter lcd size: ";
		cin>>lcd;
	}

	void all_other_info()
	{
		cout<<"Enter processor speed: ";
		cin>>pcr;
		cout<<"Enter ram size: ";
		cin>>ram;
		cout<<"Enter motherboard model: ";
		cin>>mothrbrd;
	}

	void display()
	{
		cout<<"pc name: "<<name;
		cout<<"processor speed:"<<pcr;
		cout<<"ram size: "<<ram;
		cout<<"motherboard model: "<<mothrbrd;
		cout<<"graphics card size: "<<agp;
		cout<<"lcd size: "<<lcd;
	}

	cmptr(cmptr &p)
	{
		name = p.name;
		agp = p.agp;
		lcd = p.lcd;
		
	}
};

void main()
{

here are two codes this one works good 

	
        cmptr pc1;
	cout<<"spec for 1 pc"<<endl;
	pc1.defaultinfo();
	cout<<"spec for 2 pc:"<<endl;
	cmptr pc2=pc1;   // here is copy 3 variables of pc1 not all


        pc2.all_other_info();  // here it takes pc2 remaining values

	cout<<"result of 1 pc"<<endl;
	pc1.display();
	cout<<"result of 2 pc"<<endl;
        pc2.display();

// here is the real code which i am facing problem

	int a;
	cout<<"How many pc you want:";  // here i will enter 2 pc
	cin>>a;
	cmptr *pc = new cmptr[a];
	pc[0].defaultinfo();
	cmptr pc[1]=pc[0];          <--------- i get error from here
                                    i want that some contents of pc1 array copy to
                                    pc2 array contents but not working..
}

[Unimportant]

cmptr pc[1]=pc[0]; // this is a redefinition
pc[1] = pc[0]; // this is what you actually wanted, assuming a was at least 2

cmptr *pc = new cmptr[100]; // this would be a = 100
pc[0].defaultinfo(); // both totally ok
pc[99].defaultinfo(); // both totally ok
// pc is a pointer to memory segment containing 100 copies of the cmptr object in sequential order
// the number you pass to the [] operator is an "offset", which adds the size of an object in bytes to the address of pointer &array[0]
// so, &pc + 100 bytes might be pc[1] if each object is 100 bytes in memory, but this is kind of semantics

// hence:
cmptr pc[1]; // is totally wrong, you already gave pc[1] a definition.

// Edit: don't forget to delete the memory pc points to when you are done using it:
delete[] pc;

Good luck!

[shayankhan]

cmptr pc[1]=pc[0]; // this is a redefinition
pc[1] = pc[0]; // this is what you actually wanted, assuming a was at least 2

cmptr *pc = new cmptr[100]; // this would be a = 100
pc[0].defaultinfo(); // both totally ok
pc[99].defaultinfo(); // both totally ok
// pc is a pointer to memory segment containing 100 copies of the cmptr object in sequential order
// the number you pass to the [] operator is an "offset", which adds the size of an object in bytes to the address of pointer &array[0]
// so, &pc + 100 bytes might be pc[1] if each object is 100 bytes in memory, but this is kind of semantics

// hence:
cmptr pc[1]; // is totally wrong, you already gave pc[1] a definition.

// Edit: don't forget to delete the memory pc points to when you are done using it:
delete[] pc;

Good luck!

pc[1] = pc[0]; // this is what you actually wanted, assuming a was at least 2

pc[0] whole contents are copied to pc[1] ... but i want 3 contents to be copy. i mean agp, name of pc, and lcd just copy to pc[1]
please look what i am talking about
and thanks for the advice and guide for deleting array memory ...

[Unimportant]

You did not read my post.
You had a compiler error because you redefined the array:

cmptr pc[1]=pc[0]; // this is a redefinition

You defined the copy constructor yourself, so if you want it to do something different, then change it.

cmptr(cmptr &p)
	{
		name = p.name;
		agp = p.agp;
		lcd = p.lcd;
		
	}
// you didn't add most of the variables below
class cmptr
{
private:
	string rm;
	string hd;
	string nme;
	string agp;
	string mothrbrd;
	int lcd;
	int pcr;

...?

[shayankhan]

unimportant ... i dont know how to copy array contents to other array using constructor... i will try my best...

[Unimportant]

No no, you already did it.

cmptr(cmptr &p)
{
  name = p.name;
  agp = p.agp;
  lcd = p.lcd;
}

The code above is from your code.

constructors are defined like this:

classname( args ) : class_initialization() { // post initialization code }
// in this case
cmptr( cmptr &p ) {
// means that if you construct this object with the address of this object as an argument, do whatever is where this comment is
}
// so when you create an instance of the object like this
cmptr a(); // default constructor
cmptr OTHER(a); // copy constructor, OTHER is now constructed based on the constructor that accepts an address (or pointer to) another object of the same type
// when you invoke the assignment operator '=' and you have not defined an
// overload for assignment, by default the copy constructor is invoked if the
// type is the same.
// Here we have an assignment:
cmptr pc_a();
cmptr pc_b = pc_a;
// which invokes the copy constructor

Good luck!

Edit: I changed my mind. Based on what you are doing, the assignment overload is necessary, as pc[1] would be initialized already by the default constructor when you create it with new, as you did not pass any construction arguments.

cmptr & operator=( const cmptr p ) {
  name = p.name;
  agp = p.agp;
  lcd = p.lcd;
  return *this;
}

That's an example of how to overload your assignment operator.

[shayankhan]

unimportant thanks for the help and guide ... these codes works perfect.. but you know
these are just objects that created, but my actual work is in array object.

comptr *pc = new comptr[49]; //range 1-50
as when i code this
pc[0]. blah blah();

pc[1]=pc[0];        <---- this copy all variables from pc[0] array.
comptr pc[1]=pc[0]; <------- this give me (IntelliSense: initialization with '{...}'
                                 expected for aggregate object)

i think there is no way to get array1 objects specific items and put into array 2 objects.
i search everywhere but no use so i will change my mind and code into simple 2 objects not array objects.
i really appreciate your help...

[Unimportant]

No, I told you from the start, this line of code is just wrong:
comptr pc[1] = pc[0]; // You can't do this.

Your compiler is telling you that's impossible.

pc[1] is already comptr
you are making it comptr "again"
comptr pc[1] <--- is bad because:
comptr *pc = new comptr[50]; // range 0 - 49, --> this is 50 comptr objects

This code also works:

comptr *pc; // note no new yet
pc = new comptr[50]; // there are 50 comptr objects now
// *pc is not a computer, it is a -pointer-
// it points to the beginning of the array (&comptr[0])
// pc[1] means, &comptr[0] + size in bytes of comptr (&comptr[1])

// so when you do this
pc[0].defaultinfo();
pc[1] = pc[0];
pc[2] = pc[1];
pc[3] = pc[0];

// all objects from pc[0] to pc[3] are equal to the value of pc[0]
// they are separate objects
pc[1].defaultinfo(); // now you can change pc[1]
// pc[0], pc[2], and pc[3] are still the same, they are their own object

comptr pc[4]; // ERROR. YOU ALREADY DEFINED PC[4], it is a comptr object -already-

You said:
"i think there is no way to get array1 objects specific items and put into array 2 objects."
and that's wrong, I am showing you how to do that.

[shayankhan]

ohhhhhhhh GOD i did it !!!
here what i was talking unimportant

pc[1].copydefault(pc[1] , pc[0]);

copydefault function will send two objects
and then object_1 (2 strings name agp) and (1 int lcd) value are copied to object_2
while object_1 contains 5 strings 2 int.

void copydefault(automobile &pc_1, automobile &pc_O) {
		pc_1.name = pc_O.name;
		pc_1.agp = pc_O.agp;
		pc_1.lcd = pc_O.lcd;
}

unimportant thanks about contruct and pointer actually i directly jumped
to OOP without clearing my concept of pointers & references.