Haley's Tedious Questions

[Haley]

You can include your own questions too.
I haven't taken any classes for programming. Everything I know is from tinkering around, some short lived google searches and from my cancerous experience with gamemaker.

So I want to be good, in fact I want to be the best, but right now I don't understand anything.

What do the double colons mean? It's for a project I'm editing. (someone else wrote the code) This is C++
[img]http://anyhub.net/file/1NnB-doublecolon.jpg[/img]

Don't tell me to scurry back to gamemaker, because to accomplish what I want to accomplish, gamemaker is not a practical tool.
I do want to get into programming robotics. Preferably Nano-robotic colonies.
Automated technologies make it easier being human. There are somethings I wish to automate and hasten.
Exploring the world on a micro level through Nano-robotics offers the opportunity to provide greater efficiency to technology. So yeah, I'm into that stuff. Any guidance would be swell

[pollyzoid]

:: is for accessing namespaces and [del]static[/del] members of a class. Without anything in front of it, it's the global namespace.

[Haley]

[QUOTE=raBBish;27988441]:: is for accessing namespaces and static members of a class. Without anything in front of it, it's the global namespace.[/QUOTE]

"->" are for pointers right?
and what are the "_" before the variable names? I couldn't find an answer for this anywhere

[r4nk_]

:: is the namespace qualifier (google it). ::a etc qualifies it as the a in the global namespace:

int a = 5;

void f()
{
     int a = 7;

     std::cout << a << " " << ::a;
}

[pollyzoid]

[QUOTE=Haley;27988459]"->" are for pointers right?[/QUOTE]

Yep.

[QUOTE=Haley;27988459]and what are the "_" before the variable names? I couldn't find an answer for this anywhere[/QUOTE]

It's just part of the name, some people use it to denote private members.

[Haley]

[QUOTE=r4nk_;27988467]:: is the namespace qualifier (google it). ::a etc qualifies it as the a in the global namespace:

[/QUOTE]

So this will make:
16 5 7
right?

int a = 5;

void f()
{
     int a = 7;
     g();
}

void g()
{
     int a = 16;

     std::cout << a << " " << ::a << " " << f::a;
}

@rabbish
So this would not make sense

overHere_int->3;

But this would?

overHere_int->these_Ints_overhere;

And if we want the pointer value to enter into a function we'll do this

dont_mind_me_just_calling_my_function(&overHere_int);

[ZeekyHBomb]

You can't access f::a from g. Though if you could, yes.

[r4nk_]

No you can't do that, the a in function f is only accessible from within the function (not from within functions that are called inside f..). but your output would be right if you could.

[Haley]

[QUOTE=r4nk_;27988530]No you can't do that, the a in function f is only accessible from within the function (not from within functions that are called inside f..). but your output would be right if you could.[/QUOTE]

oh yeah. cuz g() could be used outside of f... and that would leave room for errors
but I can't, so it's pointless @_@
if I wanted to pass the value in i'd have to do so with an argument or by putting it in a global variable, correct?

@rabbish
So this would not make sense

overHere_int->3;

But this would?

overHere_int->this_Int_overhere;

And if we want the pointer value to enter into a function we'll do this

dont_mind_me_just_calling_my_function(&overHere_int);

[ZeekyHBomb]

[QUOTE=Haley;27988502]So this would not make sense

overHere_int->3;

But this would?

overHere_int->these_Ints_overhere;

And if we want the pointer value to enter into a function we'll do this

dont_mind_me_just_calling_my_function(&overHere_int);

[/QUOTE]

If overHere_int is a pointer to some struct or something that has a member called these_Ints_overhere, yes.
And if overHere_int is not already a pointer, normally yes, since the unary operator & is generally used to get the address of something.

[editline]11th February 2011[/editline]

[QUOTE=Haley;27988576]oh yeah. cuz g() could be used outside of f... and that would leave room for errors[/QUOTE]
I don't see how this would create an error. If the value inside the function was a constant, then there is no technical barrier I think, but let's just leave it at "It's not possible according to the current C++ standard".

[QUOTE=Haley;27988576]if I wanted to pass the value in i'd have to do so with an argument or by putting it in a global variable, correct?[/QUOTE]

That or a variable in file-scope. People generally pass things around via parameter though.

[Haley]

[QUOTE=ZeekyHBomb;27988588]If overHere_int is a pointer to some struct or something that has a member called these_Ints_overhere, yes.
And if overHere_int is not already a pointer, normally yes, since the unary operator & is generally used to get the address of something.[/QUOTE]

Oh wait. i think i just confused you regarding what I meant.
Sorry.

overHere_int is suppose to be an address
so does this

overHere_int->these_Ints_overhere;

make overHere_int equal the address of these_Ints_overhere

[ZeekyHBomb]

No.
The operator-> is generally used to access members of pointers, similar to how you use the operator ..
[cpp]struct Foo
{
int bar;
}

int main()
{
Foo foo;
foo.bar;
Foo *pFoo = &foo;
pFoo.bar; //compiler error
pFoo->bar; //accesses bar alike foo.bar
(*pFoo).bar; //the asterisk dereferences the pointer, so now you can use the operator .; this is actually what pFoo->bar does
}[/cpp]

[Haley]

[QUOTE=ZeekyHBomb;27988652]No.
The operator-> is generally used to access members of pointers, similar to how you use the operator ..
[cpp]struct Foo
{
int bar;
}

int main()
{
Foo foo;
foo.bar;
Foo *pFoo = &foo;
pFoo.bar; //compiler error
pFoo->bar; //accesses bar alike foo.bar
(*pFoo).bar; //the asterisk dereferences the pointer, so now you can use the operator .; this is actually what pFoo->bar does
}[/cpp][/QUOTE]

pFoo is a pointer then
To "dereference" is to get the actual struct,int,string or basically the real substance behind the pointer. correct?

[Jallen]

[QUOTE=Haley;27988860]pFoo is a pointer then
To "dereference" is to get the actual struct,int,string or basically the real substance behind the pointer. correct?[/QUOTE]

Yes.
In his example, saying *pFoo is exactly the same as saying foo.

[Haley]

[QUOTE=Jallen;27988920]Yes.
In his example, saying *pFoo is exactly the same as saying foo.[/QUOTE]
Got it.

So what is the difference between and object and a struct?
oh... Objects can have member functions. structs can't.

I don't really see the benefit of that. Why no just have all your functions global? Oh, because you might want to call dance() on objects that dance differently.

I think I just answered my own question.

@_r4nk
I noticed you use "std::cout << a"
"<<" is for streams right?
What other kind of streams are there?
I guess different streams accept different variables?

[ZeekyHBomb]

I don't think an object is clearly defined for C++, though I'd use it as a synonym for a class or struct. And the only difference between those is the default visibility (private vs public).
What you might be thinking of is a [url=http://en.wikipedia.org/wiki/Plain_old_data_structure]POD[/url] type, which may not contain virtual functions (see polymorphism).

You might not want to have all your functions global, because functions may be designed to be used with certain classes.
[cpp]struct A
{
//this can be called via A a; a.doSomething();
void doSomething();
}

//A& is a reference to an A-object
//this can be called via A a; doSomething(a); and is IMO not as straight forward as a.doSomething();
void doSomething(A&);[/cpp]

<< is actually a binary left shift, but it's overloaded for std-streams. You can find various standard streams listed [url=http://www.cplusplus.com/reference/iostream/]here[/url].

[url=http://www.cplusplus.com/reference/iostream/ostream/operator%3C%3C/]These[/url] are the kind of stuff you can output via an std::ostream. In addition to that you can easily define your own rules, [url=http://www.cplusplus.com/reference/string/operator%3C%3C/]like it has been done for std::strings[/url].

[Wyzard]

[QUOTE=Haley;27989093]
So what is the difference between and object and a struct?
oh... Objects can have member functions. structs can't.
[/QUOTE]
Actually, structs can have member functions too; the only technical difference between a struct and a class in C++ is that members of structs are public by default, and members of classes are private by default.

By [i]convention[/i], though, structs are used in C++ the same way they are in C: as "dumb" data containers, rather than "smart" objects. So you typically don't put member functions in a struct. (It can be useful to add a constructor, though, to help with initializing variables when you create an instance of the struct.)

[QUOTE=Haley;27989093]
I don't really see the benefit of that. Why no just have all your functions global? Oh, because you might want to call dance() on objects that dance differently.
[/QUOTE]
It facilitates [url=http://en.wikipedia.org/wiki/Polymorphism_in_object-oriented_programming]polymorphism[/url] as you mentioned, and also associates functions with a class so that [url=http://en.wikipedia.org/wiki/Encapsulation_(object-oriented_programming)]encapsulation[/url] can be enforced by the compiler. (A private function can only be called by other functions in the same class; that can't be done with functions that aren't in any class.)

[Elspin]

I'm not saying you should give up, but you really should read up on the basic syntax of the language before you throw yourself into it, or you'll have a hard time adjusting

I started at [url]www.cplusplus.com[/url], it's definitely a good place to get your basic syntax down, and it's a handy reference for things like stl containers, arguments for standard libraries etc.

[Layla]

You're learning backwards, I did this and got nowhere.

[redonkulous]

[url]http://www.e-booksdirectory.com/details.php?ebook=3516[/url]

This is the e-book I used. It is pretty long but it explains things really really well. I can say with certainty that if you read it you will understand everything it teaches, which is pretty much all the standard c++ junk you will run into.