Programming Forums > Application Development > C++

White-Hat` · Sep 26th, 2005, 2:40 PM

Hey again. I had a question about some code I was trying out.

Quote:

#include <iostream>

using namespace std;

struct xampl {
int x;
};

int main()
{
xampl structure;
xampl *ptr;

structure.x = 12;
ptr = &structure;

cout << ptr->x;

cin.get();
}

Now I understand that the code in italics is defining the structure, but I'm not -entirely- sure what the code in bold is meaning. The tutorial is fairly vague and I would like to. My best guest would be...

Hell, it all just seems rather redundant to me. Any help is appreciated.

Edit: I do understand pointers before anyone asks. Just thought I would clarify.

Ooble · Sep 26th, 2005, 3:00 PM

When you create a structure or a class in C++, you're creating a new type to go with it. Here, you're defining a new variable, structure, of type xampl. That variable has a sort of "subvariable", or member variable - x. When you're accessing these member variables, you use a dot:

(Toggle Plain Text)

structure.x = 5;
std::cout << structure.x;

You can also create a pointer to a structure, as you can see. However, the dot ( . ) operator takes precedence over the dereference operator ( * ). That means we have to use brackets:

(Toggle Plain Text)

(*ptr).x;

Because that's a bitch to type out, we use the "pointer member" operator: ->

(Toggle Plain Text)

ptr->x;

Hope that helped.

Diamond_Don · Sep 26th, 2005, 3:22 PM

#include <iostream>

using namespace std;

struct xampl {
int x;
};
www.geocities.com/donald_ferrone
int main()
{
xampl structure;
xampl *ptr;

structure.x = 12;69696969696969
ptr = &structure;

cout << ptr->x;

cin.get();
}

HOPE THIS HELPS.

White-Hat` · Sep 26th, 2005, 4:27 PM

Yes, that definetely helped. Could you clarify what you mean by 'type' though? Hate to be a bother, but I feel that word is rather broad and I would love to understand it further. Other than that, you explained it much better than my tutorial did.

Edit: I forgot to mention what I thought by when you meant type, was that it was unique to that structure in a sense. Just doing my best to understand it. 8)

stevengs · Sep 26th, 2005, 4:38 PM

Excellent question! A simple answer: type in this context means data type or representation. One differentiates between 'built-in' and 'user defined' data types. Examples of built in types are int, double and char. The struct you defined is of course a 'user defined' type.

Type Definition

(Toggle Plain Text)

struct xampl
{
  int x;
};

The name of the type is xampl, and it is defined as struct with an integer member.

After it has been defined, you may create instances of xample, just as you would create an instance of a built in type, such as int, double or char. As Ooble stated, in main you created an instance of type xample:

(Toggle Plain Text)

xample structure;

The variable, named 'structure', represents an instance of type xample.

There is, of course, much more to be said about types, but it is probably best saved for later.

White-Hat` · Sep 26th, 2005, 4:42 PM

Oh wow. Well you learn something new everyday!

Thanks for that clarification stevengs, it makes tons more sense now. You guys sure are a lot of help over here. 8)

Ooble · Sep 27th, 2005, 12:23 PM

Glad to be of service.

Sep 26th, 2005, 3:00 PM	#2
Ooble I eat cake for breakfast. Join Date: Jul 2004 Location: In my box. Posts: 4,434 Rep Power: 9	When you create a structure or a class in C++, you're creating a new type to go with it. Here, you're defining a new variable, structure, of type xampl. That variable has a sort of "subvariable", or member variable - x. When you're accessing these member variables, you use a dot: (Toggle Plain Text) structure.x = 5; std::cout << structure.x; structure.x = 5; std::cout << structure.x; You can also create a pointer to a structure, as you can see. However, the dot ( . ) operator takes precedence over the dereference operator ( * ). That means we have to use brackets: (Toggle Plain Text) (ptr).x; (ptr).x; Because that's a bitch to type out, we use the "pointer member" operator: -> (Toggle Plain Text) ptr->x; ptr->x; Hope that helped. __________________ Me :: You :: Them

Sep 26th, 2005, 4:38 PM	#5
stevengs Professional Programmer Join Date: May 2005 Location: Bad Nauheim, Germany Posts: 436 Rep Power: 4	Excellent question! A simple answer: type in this context means data type or representation. One differentiates between 'built-in' and 'user defined' data types. Examples of built in types are int, double and char. The struct you defined is of course a 'user defined' type. Type Definition (Toggle Plain Text) struct xampl { int x; }; struct xampl { int x; }; The name of the type is xampl, and it is defined as struct with an integer member. After it has been defined, you may create instances of xample, just as you would create an instance of a built in type, such as int, double or char. As Ooble stated, in main you created an instance of type xample: (Toggle Plain Text) xample structure; xample structure; The variable, named 'structure', represents an instance of type xample. There is, of course, much more to be said about types, but it is probably best saved for later. __________________ -Steven "Is this a piece of your brain?" - Basil Fawlty Last edited by stevengs; Sep 26th, 2005 at 4:56 PM.

Sep 27th, 2005, 12:23 PM	#7
Ooble I eat cake for breakfast. Join Date: Jul 2004 Location: In my box. Posts: 4,434 Rep Power: 9	Glad to be of service. __________________ Me :: You :: Them

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Sep 26th, 2005, 3:22 PM	#3
Diamond_Don Newbie Join Date: Sep 2005 Posts: 2 Rep Power: 0	#include <iostream> using namespace std; struct xampl { int x; }; www.geocities.com/donald_ferrone int main() { xampl structure; xampl *ptr; structure.x = 12;69696969696969 ptr = &structure; cout << ptr->x; cin.get(); } HOPE THIS HELPS.

Sep 26th, 2005, 4:27 PM	#4
White-Hat` Programmer Join Date: Sep 2005 Location: Oopland Posts: 36 Rep Power: 0	Yes, that definetely helped. Could you clarify what you mean by 'type' though? Hate to be a bother, but I feel that word is rather broad and I would love to understand it further. Other than that, you explained it much better than my tutorial did. Edit: I forgot to mention what I thought by when you meant type, was that it was unique to that structure in a sense. Just doing my best to understand it. 8)

Sep 26th, 2005, 4:42 PM	#6
White-Hat` Programmer Join Date: Sep 2005 Location: Oopland Posts: 36 Rep Power: 0	Oh wow. Well you learn something new everyday! Thanks for that clarification stevengs, it makes tons more sense now. You guys sure are a lot of help over here. 8)

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Programming Forums > Application Development > C++

A question about structures