Type casting and void pointer (or, how to pass anthing in a vector)

Type casting and void pointer (or, how to pass anthing in a vector)

bicilotti

Member #9,995

July 2008

Hello Ladies and Gentlemen!

I'm working on a proc. generated platform and I came across this problem:

I want to tore in an vector some pointers to object of different nature; I searched google a bit and found a nice answer: void pointers.

The other side of the problem is a bit too complex for me: I need another function to take that vector and read it back (i.e. read whatever it's stored inside).
Direct dereferencing, I cannot do.
Typecasting manually (like passing two vectors, one containing the big messy void pointer list and another one with the type of the pointers) -> is quite useless.

In so many words my question is:

is there a way to pass a big array/vector/set with whatever inside and to get another function to read it back without creating a total mess?

I hope my question is clear, if not please tell me what you need to know. Thank you in advance!

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-= ColourWise =-

GullRaDriel

Member #3,861

September 2003

If you are using C++, maybe you are looking for polymorphism.
If you are using C, you aren't looking it the way it should be.

Please tell us what language you use, and put a little bit of code illustrating what you want. (don't forget to use the code tags).

"Code is like shit - it only smells if it is not yours"
Allegro Wiki, full of examples and articles !!

axilmar

Member #1,204

April 2001

I am guessing now but you use C++, don't you?

You need to cast the void ptr to the type you want:

vector<void *> data;
(my_object *)data[5];

ALGUI: c++11 A5 GUI library.

count

Member #5,401

January 2005

Quote:

I am guessing now but you use C++, don't you?

You need to cast the void ptr to the type you want:

vector<void *> data;
(my_object *)data[5];

And one should ad, that this cast will miserably fail when there is an object with another type in the vector then expected.

axilmar

Member #1,204

April 2001

Quote:

And one should ad, that this cast will miserably fail when there is an object with another type in the vector then expected.

Indeed, but the OP's question indicates he is not ready for boost::any or polymorphism yet.

ALGUI: c++11 A5 GUI library.

bicilotti

Member #9,995

July 2008

Thanks for the answers!

I'm using C++ (see that little icon on the left of the thread's title?).

@aximilar:

that's exactly my problem: I don't want to cast the void pointer to the type I want. (better, I don't like the solution ).

But let the code do the talk

current:

function: "hey, there's a big vector full of apples! yay!"
function: "let's sort/do something else with them!"

function: "hey, there's a big vectors of oranges" etc. etc.

It works, but it does not make me smile.

Something like:

function: "hello tiny pointer!"
pointer: "hello big function!"
function: "what kind of thing do you point to?"
pointer: "an apple!"
function: "yay, I like apples!"
pointer: "yay!"
function: "let's dereference you and do something with it!"

would do both

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Matthew Leverton

Supreme Loser

January 1999

They should inherit something from a common parent. Otherwise, I question why they need to be stored in the same vector.

--
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axilmar

Member #1,204

April 2001

Yeap, do what Matthew says:

class Fruit {
}

class Apple : Fruit {
}

class Orange : Fruit {
}

//a vector for apples and oranges
vector<Fruit *> fruits;

ALGUI: c++11 A5 GUI library.

Speedo

Member #9,783

May 2008

Quote:

I searched google a bit and found a nice answer: void pointers.

void* is rarely a nice answer. You should use them really only when you absolutely have to. Use something like boost::any instead.

bicilotti

Member #9,995

July 2008

Mhhh, seems simple enough. I'll try it and report if I've found any problem. Thanks!

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-= ColourWise =-