Source

[Default User]

Re: Source

Bill Cunningham wrote:
[color=blue]
> Then C is an object language.[/color]


C has objects. It, with some pain, can do object-oriented programming.
OO is not a natural idiom for C programming. If you want to do OO, there
are better languages.



Brian Rodenborn

[Arthur J. O'Dwyer]

Re: Source


On Thu, 9 Oct 2003, Ashish wrote:[color=blue]
>[color=green][color=darkred]
> > > "Joona I Palaste" <palaste@cc.hel sinki.fi> wrote...
> > >> Bill Cunningham <nospam@net.net > scribbled the following:
> > >>
> > >> > struct GUID (int x,int y);
> > >>
> > >> This is a syntax error in C. Would you be wanting comp.lang.c++?[/color][/color]
>
> I think he meant struct GUID {int x, int y};[/color]

That's still a syntax error in C.
But in C++, one can legally write

struct GUID
{
GUID (int x, int y); // <-- this line
};

which is very close to what Bill wrote.
In C, one can legally write

struct GUID { int x; int y; };

which is also similar (but of course
means something completely different).

-Arthur

[Severian]

Re: Source

On 9 Oct 2003 20:48:02 GMT, "Mark A. Odell" <nospam@embedde dfw.com>
wrote:
[color=blue]
>Sheldon Simms <sheldonsimms@y ahoo.com> wrote in
>news:pan.2003. 10.09.20.13.51. 785991@yahoo.co m:
>[color=green][color=darkred]
>>> But if I actually wanted a GUID object, and not a pointer to one,
>>> initialzed to zero I'd need to write:
>>>
>>> struct GUID guid = { 0 };[/color]
>>
>> Ok.
>>[color=darkred]
>>> or
>>>
>>> struct GUID guid;
>>> memset(guid, 0, sizeof guid);[/color]
>>
>> This isn't a very good idea.[/color]
>
>Are you concerned about traps? I suppose this may not be fully portable
>but I admit I am guilty of doing this quite often.[/color]

I used to do that too (back in the day using an old VAX C compiler),
but I always use the first form now. It's simpler, cleaner and works
just fine.

- Sev

[Mark McIntyre]

Re: Source

On Thu, 9 Oct 2003 15:51:02 -0400, in comp.lang.c , "Bill Cunningham"
<nospam@net.net > wrote:
[color=blue]
>
>"Mark A. Odell" <nospam@embedde dfw.com> wrote in message
>news:Xns940F9C 5FEE68Copyright MarkOdell@130.1 33.1.4...[color=green]
>>
>> But if I actually wanted a GUID object,
>>[/color]
>Then C is an object language.[/color]

C defines "Object" thus.
3.14
1 object
region of data storage in the execution environment, the contents of
which can represent values

Note that this has NOTHING to do with being object-oriented which is I
suspect what you meant.
--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.angelfire.c om/ms3/bchambless0/welcome_to_clc. html>


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[Mark McIntyre]

Re: Source

On Thu, 09 Oct 2003 21:15:32 GMT, in comp.lang.c , Matt Gregory
<bleah-no-more-spam@earthlink. net> wrote:
[color=blue]
>Mark A. Odell wrote:
>[color=green]
>> Sheldon Simms <sheldonsimms@y ahoo.com> wrote in
>> news:pan.2003.1 0.09.20.13.51.7 85991@yahoo.com :
>>[color=darkred]
>>>>struct GUID guid;
>>>>memset(guid , 0, sizeof guid);
>>>
>>>This isn't a very good idea.[/color]
>>
>>
>> Are you concerned about traps? I suppose this may not be fully portable
>> but I admit I am guilty of doing this quite often.[/color]
>
>What's wrong with it?[/color]

all-bits-zero might be a trap representation or other invalid value
for one of the data types within the GUID structure. For instance,
all-bits-zero might represent "Not a Number" for floating point, so
that if you later on tried to read it, you'd possibly coredump.
--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.angelfire.c om/ms3/bchambless0/welcome_to_clc. html>


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[David Rubin]

Re: Source

Ashish wrote:
[color=blue][color=green][color=darkred]
> > >> >> > What does the following code mean?
> > >> >>
> > >> >> > struct GUID *guid ={0};
> > >> >>
> > >> >> It initialises a pointer to struct GUID, whatever struct GUID is.
> > >> >> The pointer is currently not pointing at any struct GUID.
> > >> >>
> > >> > A struct GUID then, how would one write it. The GUID comes from MS's
> > >> > COM.
> > >>
> > >> > struct GUID (int x,int y);[/color][/color][/color]

It doesn't matter what struct GUID is because guid is only a *pointer*.
You are just initializing a pointer to the value 0. This is the same as

struct GUID *guid = 0;

or

int *p = 0;

for that matter.

[snip][color=blue][color=green]
> > If it's C then your compiler will choke on:
> > struct GUID (int x, int y);[/color]
>
> I think he meant struct GUID {int x, int y};[/color]

That is still a syntax error. ITYM

struct GUID {int x; int y;};

However, this is a moot point.

/david

--
Andre, a simple peasant, had only one thing on his mind as he crept
along the East wall: 'Andre, creep... Andre, creep... Andre, creep.'
-- unknown

[Bill Cunningham]

Re: Source


[color=blue][color=green][color=darkred]
> > >> >> > What does the following code mean?
> > >> >>
> > >> >> > struct GUID *guid ={0};
> > >> >>
> > >> >> It initialises a pointer to struct GUID, whatever struct GUID is.[/color][/color]
> The[color=green][color=darkred]
> > >> >> pointer is currently not pointing at any struct GUID.
> > >> >>
> > >> > A struct GUID then, how would one write it. The GUID comes from[/color][/color][/color]
MS's[color=blue][color=green][color=darkred]
> > > COM.
> > >>
> > >> > struct GUID (int x,int y);
> > >>
> > >> This is a syntax error in C. Would you be wanting comp.lang.c++?[/color]
> >
> > Did you read this bit?
> >[color=darkred]
> > >> > The GUID struct is already defined in COM but that doesn't help me[/color][/color]
> learn[color=green][color=darkred]
> > > the
> > >> > concept of struct. What I've seen looks like data type declarations[/color][/color]
> and[color=green][color=darkred]
> > > no
> > >> > functions.
> > >>
> > >> > struct A{
> > >> > int a;
> > >> > char b;
> > >> > double c;};
> > >>
> > >> Structs are different things in C and C++. Pick a language. If it's
> > >> really C then reply again and I will explain what structs are in C.[/color]
> >[color=darkred]
> > > C of course. This is clc. What I was saying was that I never see[/color][/color]
> functions[color=green][color=darkred]
> > > in structs. Just declared data types.[/color]
> >
> > If it's C then your compiler will choke on:
> > struct GUID (int x, int y);[/color]
>
> I think he meant struct GUID {int x, int y};
>
>[color=green]
> > The fact that there aren't any functions declared inside that struct
> > GUID doesn't help. It won't magically make the C compiler accept syntax
> > errors.
> > Therefore I still suspect your code is really C++.
> >[/color][/color]
What I'm really wanting to know I guess is how structs work and how to use
them. I used the GUID example.
For example.
typedef struct A{
int a;
double b;}/* sometimes a term */ ;
and I've seen struct A without the typedef.
What's the difference with and w/o the typedef? The structs hold data I can
see. How are they called? Is data all they hold?

This and pointers are the major sticking points for me with C. And when
there are bunches of parenthesis such as (((((*c))))))). That's confusing.
It looks like a time warp. Unions I rarely see.

Bill





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[Ashish]

Re: Source


"Arthur J. O'Dwyer" <ajo@nospam.and rew.cmu.edu> wrote in message
news:Pine.LNX.4 .58-035.03100917370 40.20686@unix45 .andrew.cmu.edu ...[color=blue]
>
> On Thu, 9 Oct 2003, Ashish wrote:[color=green]
> >[color=darkred]
> > > > "Joona I Palaste" <palaste@cc.hel sinki.fi> wrote...
> > > >> Bill Cunningham <nospam@net.net > scribbled the following:
> > > >>
> > > >> > struct GUID (int x,int y);
> > > >>
> > > >> This is a syntax error in C. Would you be wanting comp.lang.c++?[/color]
> >
> > I think he meant struct GUID {int x, int y};[/color]
>
> That's still a syntax error in C.
> But in C++, one can legally write
>[/color]

Sorry, I meant struct GUID {int x; int y;};

[color=blue]
> struct GUID
> {
> GUID (int x, int y); // <-- this line
> };
>
> which is very close to what Bill wrote.
> In C, one can legally write
>
> struct GUID { int x; int y; };
>
> which is also similar (but of course
> means something completely different).
>
> -Arthur[/color]

[Jack Klein]

Re: Source

On Thu, 09 Oct 2003 23:50:41 +0100, Mark McIntyre
<markmcintyre@s pamcop.net> wrote in comp.lang.c:
[color=blue]
> On Thu, 9 Oct 2003 15:51:02 -0400, in comp.lang.c , "Bill Cunningham"
> <nospam@net.net > wrote:
>[color=green]
> >
> >"Mark A. Odell" <nospam@embedde dfw.com> wrote in message
> >news:Xns940F9C 5FEE68Copyright MarkOdell@130.1 33.1.4...[color=darkred]
> >>
> >> But if I actually wanted a GUID object,
> >>[/color]
> >Then C is an object language.[/color]
>
> C defines "Object" thus.
> 3.14
> 1 object
> region of data storage in the execution environment, the contents of
> which can represent values
>
> Note that this has NOTHING to do with being object-oriented which is I
> suspect what you meant.[/color]

....and C++ describes it equivalently, using more words:

1.8 The C++ object model
1 The constructs in a C++ program create, destroy, refer to, access,
and manipulate objects. An object is a region of storage. [Note: A
function is not an object, regardless of whether or not it occupies
storage in the way that objects do. ] An object is created by a
definition (3.1), by a new expression
(5.3.4) or by the implementation (12.2) when needed. The properties of
an object are determined when the object is created.
An object can have a name (clause 3). An object has a storage duration
(3.7) which influences its lifetime
(3.8). An object has a type (3.9). The term object type refers to the
type with which the object is created.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.l earn.c-c++ ftp://snurse-l.org/pub/acllc-c++/faq

[Richard Heathfield]

Re: Source

Bill Cunningham wrote:
[color=blue]
> What I'm really wanting to know I guess is how structs work and how to use
> them.[/color]

They work the same way ints work. They're just types, that's all.
[color=blue]
> I used the GUID example.
> For example.
> typedef struct A{
> int a;
> double b;}/* sometimes a term */ ;[/color]

This is a syntax error.

typedef struct A{
int a;
double b;} A;

would not be a syntax error, however. Here is the typedef again, this time
on a single line:

typedef struct A{ int a; double b;} A;

Here it is again, perhaps slightly less confusingly:

typedef struct A_tag { int a; double b;} A;


There are two parts here, which I'll separate out vertically for you:

xxxxxxx struct A_tag { int a; double b;} xx

typedef xxxxxxxxxxxxxxx xxxxxxxxxxxxxxx xx A;

There's the typedef (something-as) A, and there's the struct definition.

Put them together, and you are defining A as an alias for struct A_tag.
[color=blue]
> and I've seen struct A without the typedef.
> What's the difference with and w/o the typedef?[/color]

typedef creates a new synonym for an existing type. So, once the compiler
has seen the above example, you can use A wherever you would previously
have used struct A_tag - if you wish. To confuse matters, the tag is
allowed to be the same as the new type.
[color=blue]
> The structs hold data I
> can see. How are they called?[/color]

You don't call a struct. It's just a bunch of data.
[color=blue]
> Is data all they hold?[/color]

Yes. That data can, in fact, include pointers to functions, but they're just
data too.
[color=blue]
> This and pointers are the major sticking points for me with C.[/color]

Get a better C book, then.
[color=blue]
> And when
> there are bunches of parenthesis such as (((((*c))))))). That's confusing.[/color]

This reduces to *c)) which (on its own) is a syntax error. Don't be confused
by syntax errors. Just fix them.

--
Richard Heathfield : binary@eton.pow ernet.co.uk
"Usenet is a strange place." - Dennis M Ritchie, 29 July 1999.
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html
K&R answers, C books, etc: http://users.powernet.co.uk/eton

[Richard Heathfield]

Re: Source

Mark A. Odell wrote:
[color=blue][color=green][color=darkred]
>>> struct GUID guid;
>>> memset(guid, 0, sizeof guid);[/color]
>>
>> This isn't a very good idea.[/color]
>
> Are you concerned about traps? I suppose this may not be fully portable
> but I admit I am guilty of doing this quite often.[/color]

That's certainly an issue if the struct contains non-integer types, but I'm
more worried about compiler diagnostics. Look at your first argument to
memset again, more closely. Then look up the definition of memset.

--
Richard Heathfield : binary@eton.pow ernet.co.uk
"Usenet is a strange place." - Dennis M Ritchie, 29 July 1999.
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html
K&R answers, C books, etc: http://users.powernet.co.uk/eton

[Mark Gordon]

Re: Source

On Thu, 09 Oct 2003 21:15:32 GMT
Matt Gregory <bleah-no-more-spam@earthlink. net> wrote:
[color=blue]
> Mark A. Odell wrote:
>[color=green]
> > Sheldon Simms <sheldonsimms@y ahoo.com> wrote in
> > news:pan.2003.1 0.09.20.13.51.7 85991@yahoo.com :
> >[color=darkred]
> >>>struct GUID guid;
> >>>memset(gui d, 0, sizeof guid);
> >>
> >>This isn't a very good idea.[/color]
> >
> >
> > Are you concerned about traps? I suppose this may not be fully
> > portable but I admit I am guilty of doing this quite often.[/color]
>
> What's wrong with it?[/color]

It sets all bits zero. Unfortunately all bits set to zero could be a
trap representation for some of the elements of struct GUID depending
on that type they are.
--
Mark Gordon
Paid to be a Geek & a Senior Software Developer
Although my email address says spamtrap, it is real and I read it.

[Dan Pop]

Re: Source

In <Xns940FAAE74BF 66CopyrightMark Odell@130.133.1 .4> "Mark A. Odell" <nospam@embedde dfw.com> writes:
[color=blue]
>Sheldon Simms <sheldonsimms@y ahoo.com> wrote in
>news:pan.2003. 10.09.20.13.51. 785991@yahoo.co m:
>[color=green][color=darkred]
>>> But if I actually wanted a GUID object, and not a pointer to one,
>>> initialzed to zero I'd need to write:
>>>
>>> struct GUID guid = { 0 };[/color]
>>
>> Ok.
>>[color=darkred]
>>> or
>>>
>>> struct GUID guid;
>>> memset(guid, 0, sizeof guid);[/color]
>>
>> This isn't a very good idea.[/color]
>
>Are you concerned about traps? I suppose this may not be fully portable
>but I admit I am guilty of doing this quite often.[/color]

Not necessarily traps, but non-integer structure members may not be
initialised to zero or null pointers. Of course, this is an issue only
when portability to weird platforms is a valid concern (neither null
pointers nor floating point zero need be represented as all bits zero).

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Dan.Pop@ifh.de

[Mark A. Odell]

Re: Source

Richard Heathfield <dontmail@addre ss.co.uk.invali d> wrote in
news:bm5l54$j72 $2@hercules.bti nternet.com:
[color=blue][color=green][color=darkred]
>>>> struct GUID guid;
>>>> memset(guid, 0, sizeof guid);
>>>
>>> This isn't a very good idea.[/color]
>>
>> Are you concerned about traps? I suppose this may not be fully portable
>> but I admit I am guilty of doing this quite often.[/color]
>
> That's certainly an issue if the struct contains non-integer types, but
> I'm more worried about compiler diagnostics. Look at your first argument
> to memset again, more closely. Then look up the definition of memset.[/color]

Yikes!

memset(&guid, 0, sizeof guid);

I will, from this point forth, no longer use memset() on structs even if I
know it contains no data types that can have trap values.

--
- Mark ->
--

[Bill Cunningham]

Re: Source

So the character after the last } of a struct and before ; is for a typedef?
What about this.

struct A{
int a;
*_point;}Ab; /* is the Ab an alias? */

Bill





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