C programmers! How do you use your 'union's ?

[Razmig K]

Dear mates,

This is an another survey for the common (and uncommon) nontrivial
uses of the aforementioned C construct.
It's posted by the same average C programmer who's made a similar
survey about the uses of 'enum's.

I know that space optimization is the key idea behind 'union's, and in
most cases a type-field is necessary to verify the type of the entity
in the 'union' variable.

I'm just curious about how my elder colleagues utilize this feature of
C in their implementations based on diverse programming styles in
diverse application domains.

Thank you for your interest.

Best regards,
//rk

[Malcolm]

"Razmig K" <st*********@po stmaster.co.uk> wrote in message

This is an another survey for the common (and uncommon) nontrivial
uses of the aforementioned C construct.
My programs are pretty much a union-free zone.
I'm just curious about how my elder colleagues utilize this feature of
C in their implementations based on diverse programming styles in
diverse application domains.

One place unions are used is in the X Window system. The idea is that the
client and the X server can reside on different machines, and packets can go
over a network. An obvious optimisation is to make each packet of fixed
size, with a type field telling you how to interpret the data - a mouse
click, a request to redraw, etc. The messages are therefore implemented as
unions.

[Programmer Dude]

Malcolm wrote:

My programs are pretty much a union-free zone.

Another vote for: Likewise
--
|_ CJSonnack <Ch***@Sonnack. com> _____________| How's my programming? |
|_ http://www.Sonnack.com/ _______________ ____| Call: 1-800-DEV-NULL |
|______________ _______________ _______________ _|_____________ __________|

[Severian]

On 15 Aug 2003 09:29:12 -0700, st*********@pos tmaster.co.uk (Razmig K)
wrote:

Dear mates,

This is an another survey for the common (and uncommon) nontrivial
uses of the aforementioned C construct.
It's posted by the same average C programmer who's made a similar
survey about the uses of 'enum's.

I know that space optimization is the key idea behind 'union's, and in
most cases a type-field is necessary to verify the type of the entity
in the 'union' variable.

I'm just curious about how my elder colleagues utilize this feature of
C in their implementations based on diverse programming styles in
diverse application domains.

In my largest project, 10 years old and going strong, I found exactly
*two* uses of 'union' in ~500K lines of C code.

And were I refactoring either area of the code base today, I would get
rid of them.

- Sev

[Peter Ammon]

Razmig K wrote:

Dear mates,

This is an another survey for the common (and uncommon) nontrivial
uses of the aforementioned C construct.
It's posted by the same average C programmer who's made a similar
survey about the uses of 'enum's.

I know that space optimization is the key idea behind 'union's, and in
most cases a type-field is necessary to verify the type of the entity
in the 'union' variable.

I'm just curious about how my elder colleagues utilize this feature of
C in their implementations based on diverse programming styles in
diverse application domains.

Thank you for your interest.

Best regards,
//rk

I use unions in my "ooze" code. An ooze is an abstract input stream
that can represent either a string or a file. Mr. Heathfield's
thesaurus deserves credit for the name.

For your viewing pleasure:
http://homepage.mac.com/gershwin/temp/ooze.h
http://homepage.mac.com/gershwin/temp/ooze.c

Oh, and the license for this stuff (just in case)
http://www.people.cornell.edu/pages/...ss/license.txt

-Peter

[istartedi]

Razmig K <st*********@po stmaster.co.uk> wrote in message
news:3c******** *************** *@posting.googl e.com...

Dear mates,

This is an another survey for the common (and uncommon) nontrivial
uses of the aforementioned C construct.
It's posted by the same average C programmer who's made a similar
survey about the uses of 'enum's.

I use unions in a stack-based VM. Several different types can be pushed
onto the same stack. I'm hard pressed to think of something more elegant
than unions for that.

I missed the poll on enums. I never use them. I always #define stuff.

Now next you'll probably ask about gotos. I was taught to be a goto snob by
more than one professor. Recently though, I've loosed up and used some
gotos for functions that require extensive "clean up" before returning.

--$teve

[istartedi]

Peter Ammon <pe*********@ro cketmail.com> wrote in message
news:bh******** **@news.apple.c om...
[snip]

Oh, and the license for this stuff (just in case)
http://www.people.cornell.edu/pages/...ss/license.txt
Holy horizontals, Batman!

There are no line terminators. Quick, the Bat-cariage!
return that is... (groan).

--$teve

-Peter

[William Ahern]

istartedi <co******@vrml3 d.com> wrote:

Peter Ammon <pe*********@ro cketmail.com> wrote in message
news:bh******** **@news.apple.c om...
[snip]

Oh, and the license for this stuff (just in case)
http://www.people.cornell.edu/pages/...ss/license.txt

Holy horizontals, Batman!

There are no line terminators. Quick, the Bat-cariage!
return that is... (groan).

it is copyright "April 1st"....

[Joe Wright]

istartedi wrote:

Peter Ammon <pe*********@ro cketmail.com> wrote in message
news:bh******** **@news.apple.c om...
[snip]

Oh, and the license for this stuff (just in case)
http://www.people.cornell.edu/pages/...ss/license.txt

Holy horizontals, Batman!

There are no line terminators. Quick, the Bat-cariage!
return that is... (groan).

First, its carriage. Or maybe carrier. Think typewriters.
The IBM Model B had a carriage. That was the mechanism which held the
platen and therefore the paper and moved it (through escapes) past a
fixed print mechanism. The Teletype printers and the IBM Selectric have
fixed platen (paper) and moving print mechanisms called carriers. So
what does CR mean after all? Sorry. :-)
--
Joe Wright mailto:jo****** **@earthlink.ne t
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---

[Kevin Easton]

Razmig K <st*********@po stmaster.co.uk> wrote:

Dear mates,

This is an another survey for the common (and uncommon) nontrivial
uses of the aforementioned C construct.
It's posted by the same average C programmer who's made a similar
survey about the uses of 'enum's.

I know that space optimization is the key idea behind 'union's, and in
most cases a type-field is necessary to verify the type of the entity
in the 'union' variable.

I'm just curious about how my elder colleagues utilize this feature of
C in their implementations based on diverse programming styles in
diverse application domains.

One use for unions is if you have a data structure - say, a binary tree
- where the data carried by a node depends on its type:

struct node {
struct node *child_left, *child_right;
enum { NODE_TYPE_A, NODE_TYPE_B, NODE_TYPE_C } type;
union {
struct {
int x;
char *y;
char *z;
} type_a;
struct {
int x;
void *y;
} type_b;
struct {
struct tm x;
long int y;
} type_c;
} data;
};

One place this example in particular appears is building expression
parse trees.

- Kevin.