questions

[Guest]

1. In Java there is a class named HashTable. Is there something similar in C++?
I mean something like:
-----
hash["my_name"] = "paul";
hash["my_mail"] = "spam@here.now" ;
-----

2. we have this code:
-----------------
class A { ... };
class B : A { ... };
void GiveMeAClass(A &a) { ... }
-----------------
In function GiveMeAClass we can pass an A or B object too.
Is there a method inside GiveMeAClass to determine in run-time if passed object is from A or B?
Something like Java's keyword 'instanceof'
I believe not, but hope will die last ;-)

Thanks

[Ron Natalie]

Re: questions


"<- Chameleon ->" <cham_gss@hotma il.NOSPAM.com> wrote in message news:bknlc6$p54 $1@nic.grnet.gr ...[color=blue]
> 1. In Java there is a class named HashTable. Is there something similar in C++?
> I mean something like:
> -----
> hash["my_name"] = "paul";
> hash["my_mail"] = "spam@here.now" ;[/color]

The standard language doesn't support hashing, but the standard map class has the
semantics you want (it internally uses a tree representation) .

#include <map>
#include <string>
using namespace std;

map<string, string> hash;

hash["my_name"] = "paul";

and so forth.
[color=blue]
> 2. we have this code:
> -----------------
> class A { ... };
> class B : A { ... };
> void GiveMeAClass(A &a) { ... }
> -----------------
> In function GiveMeAClass we can pass an A or B object too.
> Is there a method inside GiveMeAClass to determine in run-time if passed object is from A or B?
> Something like Java's keyword 'instanceof'
> I believe not, but hope will die last ;-)[/color]

Well, in your above example, you can't pass a B to GiveMeAClass (since you didn't make A publicly
inheritted). However if you fix that, and you make A polymorhphic (that is, make it have at least one
virtual function), you can:

void GiveMeAClass(A& a) {
if(dynamic_cast <A*>(&a))
cout << "Give me an A!\n";
else if(dynamic_cast <B*>(&b))
cout << "Give me a B!\n";
else
cout << "What is this?\n";
}
}

Alternatively you could do a similar thing with typeinfo:

if(typeid(a) == typeid (A))


There are small subtle differences between the two but you get the idea.

[Guest]

Re: questions

> > 1. In Java there is a class named HashTable. Is there something similar in C++?[color=blue][color=green]
> > I mean something like:
> > -----
> > hash["my_name"] = "paul";
> > hash["my_mail"] = "spam@here.now" ;[/color]
>
> The standard language doesn't support hashing, but the standard map class has the
> semantics you want (it internally uses a tree representation) .
>
> #include <map>
> #include <string>
> using namespace std;
>
> map<string, string> hash;
>
> hash["my_name"] = "paul";
>
> and so forth.
>[color=green]
> > 2. we have this code:
> > -----------------
> > class A { ... };
> > class B : A { ... };
> > void GiveMeAClass(A &a) { ... }
> > -----------------
> > In function GiveMeAClass we can pass an A or B object too.
> > Is there a method inside GiveMeAClass to determine in run-time if passed object is from A or B?
> > Something like Java's keyword 'instanceof'
> > I believe not, but hope will die last ;-)[/color]
>
> Well, in your above example, you can't pass a B to GiveMeAClass (since you didn't make A publicly
> inheritted). However if you fix that, and you make A polymorhphic (that is, make it have at least one
> virtual function), you can:
>
> void GiveMeAClass(A& a) {
> if(dynamic_cast <A*>(&a))
> cout << "Give me an A!\n";
> else if(dynamic_cast <B*>(&b))
> cout << "Give me a B!\n";
> else
> cout << "What is this?\n";
> }
> }
>
> Alternatively you could do a similar thing with typeinfo:
>
> if(typeid(a) == typeid (A))
>
>
> There are small subtle differences between the two but you get the idea.[/color]

Thankyou very much!