The general consensus I am getting is that nobody really uses unions
much (engineers here at work) but this is an academic exercise for me
so I am looking for an answer (I know there may be better ways to do
this ;-) ).
What I need to know is how to write the function prototype and the
function definition for a function that returns a union.
For example: Here is a class for a double linked list in which variable
data is going to be stored. I decided a union would be a good way to go
class Node
{
public:
Node();
Node * getPrev();
Node * getNext();
Node * appendNode();
void storeVal();
int getVal(Type);
char getVal(Type);
union getVal(); <<<< I know this is wrong thats why I need help
private:
Node * nextNode;
Node * prevNode;
Node * currentNode;
union
{
int intVal;
char charVal;
char * strVal;
};
};
in the implementation file I have
this:
union Node::getVal()
{
return strVal;
}
All I am asking is 1.) is it possible to return a union type
and 2.) if so how do you instrument it in code (declaration and
definition)
Thanks one and all for your help
SteveM 8 1620
SteveM wrote: The general consensus I am getting is that nobody really uses unions much (engineers here at work) but this is an academic exercise for me so I am looking for an answer (I know there may be better ways to do this ;-) ).
What I need to know is how to write the function prototype and the function definition for a function that returns a union. For example: Here is a class for a double linked list in which variable data is going to be stored. I decided a union would be a good way to go
class Node { public: Node(); Node * getPrev(); Node * getNext(); Node * appendNode(); void storeVal(); int getVal(Type); char getVal(Type); union getVal(); <<<< I know this is wrong thats why I need help
'union' is a keyword, it doesn't define a type. So, the compiler might
see this and ask you, "<union> WHAT?". You might want to tell it
union MyUnion getVal();
and then make sure you define 'MyUnion' as below. There is no sense to
simply omit the name of the union just because. Give it a name and use
the name where you need it. private: Node * nextNode; Node * prevNode; Node * currentNode; union { int intVal; char charVal; char * strVal; };
};
in the implementation file I have this:
union Node::getVal() { return strVal; }
All I am asking is 1.) is it possible to return a union type and 2.) if so how do you instrument it in code (declaration and definition)
class HasUnion {
public:
union MyUnion {
char c;
int i;
};
MyUnion myMemberFunctio n();
};
V
Yes this is the piece of the puzzle I was missing.
Sorry I probably should have known this but as is clearly evident I am
a novice level C++ programer.
This helped me to understand unions better also and I appreciate your
speedy reply
Thanks
SteveM
SteveM wrote: The general consensus I am getting is that nobody really uses unions much (engineers here at work) but this is an academic exercise for me so I am looking for an answer (I know there may be better ways to do this ;-) ).
What I need to know is how to write the function prototype and the function definition for a function that returns a union. For example: Here is a class for a double linked list in which variable data is going to be stored. I decided a union would be a good way to go
[snip]
Scott Meyers calls unions "that old battle axe of the C world" and
makes use of them in _More Effective C++_'s Item 28. That demonstrates
that C++ programs can use unions and occasionally must do so, but
generally, they're discouraged in favor of other constructs such as
templates or boost::any (see http://boost.org/doc/html/any.html). In
particular, your doubly linked list that could store values could be
represented as a std::list<boost ::any> (cf. http://www.sgi.com/tech/stl/List.html).
Oh, and I did notice that you said "I know there may be better ways to
do this [but I'm not asking about those ways]", but I decided to ignore
that part. :-P
Cheers! --M
SteveM wrote: Yes this is the piece of the puzzle I was missing.
Which puzzle?
Brian
--
Please quote enough of the previous message for context. To do so from
Google, click "show options" and use the Reply shown in the expanded
header.
Why the puzzle of "life the universe and everything" no wait that was a
movie I saw the other night... besides we already know the answer to
that one being 42
No to me the way to use unions in the context that I visualized was a
puzzle (with some very missing pieces :P)
just a figurative way of speaking
-SteveM
Victor Bazarov wrote: SteveM wrote: All I am asking is 1.) is it possible to return a union type and 2.) if so how do you instrument it in code (declaration and definition)
class HasUnion { public: union MyUnion { char c; int i; };
MyUnion myMemberFunctio n(); };
Note that this is mostly useless, because the caller has no way
of knowing which member of the union is the one currently in use.
Any method that the caller can use to find out which member is
currently in use, would be more complicated than just having a
function that returns that member by itself.
SteveM wrote: Why the puzzle of "life the universe and everything" no wait that was a movie I saw the other night... besides we already know the answer to that one being 42
I haven't seen the movie up to now, but ....
read the book. It is impossible for the movie to be
as good as the book.
--
Karl Heinz Buchegger kb******@gascad .at
Karl Heinz Buchegger <kb******@gasca d.at> schrieb: I haven't seen the movie up to now, but .... read the book. It is impossible for the movie to be
*The* Book? There are five books in the trilogy.
as good as the book.
But still it is. And even better, because D. Adams (Gott hab' ihn selig)
has worked on refining the script until he logged off. There are some
things (jokes, citations, ...) in the movie that you couldn't imagine,
even if you knew the books by heart (auswendig?).
Markus This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
by: David |
last post by:
Some developers in my group are using UNIONS to define their data
types in a C++ program for an embedded system. Are there any pro and
cons in doing this when you can define a CLASS to do the same thing?
I guess there might be some additional overhead with CLASSES, but is
that really an issue with today's computers?
|
by: Neil Zanella |
last post by:
Hello,
I would like to know whether the following C fragment is legal in
standard C and behaves as intended under conforming implementations...
union foo {
char c;
double d;
};
|
by: Tim Cambrant |
last post by:
Hi. I was reading up a bit on the features of C I seldom use, and I came
across unions. I understand the concept, and that all the contained
variables etc. share the same memory. Thus, when a new value is declared to
a variable in the union, the existing value is overwritten even though the
new value is declared to a different variable than that of the first value.
Now I'm just wondering what the use of this is. I'm sure there are lots,...
|
by: rohit |
last post by:
Hi,
In my couple of years of experience, I have never found a single
instance where I needed to use unions and bitfields(though I have used
structures).I was just imagining where would these find
relevance.Though both of these(bitfields and unions) are used where
space is a constraint(so I can assume always in embedded systems,where
memory is particularly less)and we want to save space/memory.
As far as I have read, there is no...
|
by: Danny Mavromatis |
last post by:
I have a chunk of VC.NET code (below) that I need to convert to VB.NET
syntax. Could someone help me get started? I'm new to structures and
unions and I don't understand how to nest then in VB.NET.
' ----- VC.NET CODE THAT I NEED TO CONVERT TO VB.NET ----
struct R_OMNI_LINK_MESSAGE {
//unsigned char StartChar;
unsigned char MessageLength;
union {
| |
by: uralmutlu |
last post by:
Hi,
I was wandering if I can have classes in unions?
I basically have source code in a format very similar to:
union example {
ClassA variable1;
ClassB variable2;
};
|
by: bluejack |
last post by:
A recent post asking for help with unions reminded me of this
component of the C language that I have only used a couple of times,
and those almost entirely out of personal whim -- Unions for the sake
of Unions simply because I wanted to see one in action.
Granted: it makes it possible to save a few bytes of storage when you
have something that can be a chicken or a rooster, but not both, and
you're always going to know which it is.
...
|
by: Old Wolf |
last post by:
Ok, we've had two long and haphazard threads about unions recently,
and I still don't feel any closer to certainty about what is permitted
and what isn't. The other thread topics were "Real Life Unions"
and "union {unsigned char u; ...} ".
Here's a concrete example:
#include <stdio.h>
int main(void)
|
by: pereges |
last post by:
Hello, can some one please guide me a little into using unions. I read
about unions in K & R but I am finding it difficult to apply to my
problem at hand. I want to save up some space by using unions . My
questions are :
1. Is it dangerous to use unions ? Is it worth the trouble if I want
to save memory ? Are they error prone ?
2. I read that it is not possible to access more than 1 member at any
instant from a union. What does this...
|
by: marktang |
last post by:
ONU (Optical Network Unit) is one of the key components for providing high-speed Internet services. Its primary function is to act as an endpoint device located at the user's premises. However, people are often confused as to whether an ONU can Work As a Router. In this blog post, we’ll explore What is ONU, What Is Router, ONU & Router’s main usage, and What is the difference between ONU and Router. Let’s take a closer look !
Part I. Meaning of...
|
by: Hystou |
last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it.
First, let's disable language synchronization. With a Microsoft account, language settings sync across devices. To prevent any complications,...
| |
by: Oralloy |
last post by:
Hello folks,
I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>".
The problem is that using the GNU compilers, it seems that the internal comparison operator "<=>" tries to promote arguments from unsigned to signed.
This is as boiled down as I can make it.
Here is my compilation command:
g++-12 -std=c++20 -Wnarrowing bit_field.cpp
Here is the code in...
|
by: Hystou |
last post by:
Overview:
Windows 11 and 10 have less user interface control over operating system update behaviour than previous versions of Windows. In Windows 11 and 10, there is no way to turn off the Windows Update option using the Control Panel or Settings app; it automatically checks for updates and installs any it finds, whether you like it or not. For most users, this new feature is actually very convenient. If you want to control the update process,...
|
by: agi2029 |
last post by:
Let's talk about the concept of autonomous AI software engineers and no-code agents. These AIs are designed to manage the entire lifecycle of a software development project—planning, coding, testing, and deployment—without human intervention. Imagine an AI that can take a project description, break it down, write the code, debug it, and then launch it, all on its own....
Now, this would greatly impact the work of software developers. The idea...
|
by: isladogs |
last post by:
The next Access Europe User Group meeting will be on Wednesday 1 May 2024 starting at 18:00 UK time (6PM UTC+1) and finishing by 19:30 (7.30PM).
In this session, we are pleased to welcome a new presenter, Adolph Dupré who will be discussing some powerful techniques for using class modules.
He will explain when you may want to use classes instead of User Defined Types (UDT). For example, to manage the data in unbound forms.
Adolph will...
|
by: conductexam |
last post by:
I have .net C# application in which I am extracting data from word file and save it in database particularly. To store word all data as it is I am converting the whole word file firstly in HTML and then checking html paragraph one by one.
At the time of converting from word file to html my equations which are in the word document file was convert into image.
Globals.ThisAddIn.Application.ActiveDocument.Select();...
|
by: 6302768590 |
last post by:
Hai team
i want code for transfer the data from one system to another through IP address by using C# our system has to for every 5mins then we have to update the data what the data is updated we have to send another system
| |
by: muto222 |
last post by:
How can i add a mobile payment intergratation into php mysql website.
| |