Create new public variable from method.

[Kip]

Hi,

I'm trying to create a new public variable in a function.

Example:

class MyClass
    {
    
    public:
        
        int hellow;
        
        
        MyClass() {
              long this->newvar; // doesnt work. (ofcourse), But I hope you'll get the idea.
              // I want it to be created in the same scope as 'hellow'
        }
};

Somebody knows how to do it?

Thanks.

[jvanegmond]

You can't do that.

[Kip]

Hmm. Well, is there a way to change the datatype of Hellow? Because that was all I was trying to do.

[ProgAndy]

why do you have to change a datatype? I think that's not possible.

[James]

I assumed he wants something like TypeDef but then he can't have two things with the same name (Kip )

[Valik]

Kip, this is a case where you need to describe what problem you are trying to solve rather than try some implementation that doesn't make sense for the language. C++ is a heavily typed language. What you are asking to do makes no sense in C++. Without an adequate description of what exactly you hope to achieve, there's no way to offer a C++ solution to the problem.

[Kip]

something like this: (and this is just a very short example)

typedef int MyType;

MyType var = 9;

typedef double MyType;

var = 9.896;

[Valik]

It's still not clear if you want a variant or if you can get by with using a union. I'm thinking you want a variant, however.

[Kip]

Not really a variant, I don't want it to be able to hold all kinds of datatypes.

I just want it to hold one datatype, and let the type change.

You can say it's like a variant, yes.

this is a variant:

variant Hi = "you";
Hi = 9;
Hi = 9.827434;

and this is what I want:

int Hi = 8;
switch_type<string>(Hi); //or whatever is needed to change the datatype.
Hi = "you";
switch_type<double>(Hi);
Hi = 9.28372;

Edited March 22, 2009 by Kip

[Valik]

Does a union do what you want? You're being very vague and contradictory so it's hard to suggest anything.

[Kip]

No, I just updated my previous post, please take a look at the examples.

[Valik]

... so you want a variant.

[Kip]

No, I want a function (or whatever) to change the datatype. If I wanted a variant I would have used Boost.

Edited March 22, 2009 by Kip

[Valik]

Wow you're dumb. Have fun.

[Ascend4nt]

Kip, I think you really should use a Union. And then just access the type you want set. MyVar.AsCharPtr="String", MyVar.AsInt=14. Of course, it can only store one value at a time - and you need to make sure the Union contains the largest type of object you wish to hold, plus a mechanism for determining which type is the 'current' type (where a structure/class would come in)

[cppman]

Not really a variant, I don't want it to be able to hold all kinds of datatypes.

I just want it to hold one datatype, and let the type change.

You can say it's like a variant, yes.

this is a variant:

variant Hi = "you";
   Hi = 9;
   Hi = 9.827434;

and this is what I want:

int Hi = 8;
   switch_type<string>(Hi); //or whatever is needed to change the datatype.
   Hi = "you";
   switch_type<double>(Hi);
   Hi = 9.28372;

You can't. You could, however, if C++ was an interpreted language (and it supported such a strange feature). Since C++ is not interpreted, it has to know what data-type a variable is in order to generate the proper assembly.

Why do you not want to use a variant? It would have the same effect except the "switch_type<blah>()" would be implied.

[Kip]

Why do you not want to use a variant? It would have the same effect except the "switch_type<blah>()" would be implied.

Yeah, I'm using it now.

[JSThePatriot]

Not fun to program with, but it is available static_cast<int>(MyType) static_cast<double>(MyType), or alternately any of the *_cast<>() functions. Again, I wouldn't recommend this as it's still not plain what you're trying to really accomplish, and if you have it solved anyways no biggie. Was trying to provide some further assistance.

Jarvis

[Ascend4nt]

Can someone point me to a good source or recommend a book that describes 'Variants'? There is no mention of it in any of the books I have on C++ (though somewhat dated), but even the C++ standard docs describe only unions as having variant data, and there's some references to it regarding the Component Object Model, but only simple descriptions.

'VARIANT' doesn't look like a native data type, and I'm just wondering where to go to get a good description on it.

Thanks.

*edit: argh, nm - forgot to search MSDN. Here's the 'VARIANT and VARIANTARG' link.

Edited March 24, 2009 by ascendant

[Richard Robertson]

Variant is a composite type made of multiple native types or composite types contained together OR an untyped pointer to a native type or composite type. Apart from this field is an optional field for storing the original type of the data and a number of functions for converting between types.

I've got a working .Net variant. It's tedious to write in a strongly typed language.