Pointer question

[Erik]

Hi,
to swap the integer variables a,b,
in Kerninghan-Ritchie I find the function example

Swap(&a,&b);

unsing a function

void swap (int *px, int *py)
{
int temp;
temp:= *px;
*px = *py;
*py = temp
}

Now here I have a problem understanding that.
The function gets two !Pointers! an arguments.

So as far as I see *px=&a will happen, but *px is an integer
variable and &a is a pointer. But I think px=&a would be
correct.

????
Thanks in advance
Erik

[Christian Bau]

Re: Pointer question

In article <c16042a8.04072 72357.1d21584@p osting.google.c om>,
temporary1234@q uantentunnel.de (Erik) wrote:
[color=blue]
> Hi,
> to swap the integer variables a,b,
> in Kerninghan-Ritchie I find the function example
>
> Swap(&a,&b);
>
> unsing a function
>
> void swap (int *px, int *py)
> {
> int temp;
> temp:= *px;
> *px = *py;
> *py = temp
> }[/color]

You should really try hard to get your spelling correct. The code that
you wrote has no chance of ever compiling, and even if it did, what does
the function "swap" have to do with the function "Swap" that you are
trying to call?

I am sure that Mr. Ritchie has never written a book together with anyone
by the name of Kerninghan. I know the word "sing" but I have no idea
what you mean by "unsing". If you think I am too pedantic, then
programming is not for you.

[Ramiro Rodriguez]

Re: Pointer question

> So as far as I see *px=&a will happen, but *px is an integer[color=blue]
> variable and &a is a pointer. But I think px=&a would be
> correct.
>
> ????
> Thanks in advance
> Erik[/color]

In the function declaration px is declared as a variable of type int*. *px
is not the variable that gets set when the function is called it is px
which gets set to &a.

-RR

[Rowland]

Re: Pointer question


"Christian Bau" <christian.bau@ cbau.freeserve. co.uk> wrote in message
news:christian. bau-5D99B5.09123528 072004@slb-newsm1.svr.pol. co.uk...[color=blue]
> In article <c16042a8.04072 72357.1d21584@p osting.google.c om>,
> temporary1234@q uantentunnel.de (Erik) wrote:
>[color=green]
> > Hi,
> > to swap the integer variables a,b,
> > in Kerninghan-Ritchie I find the function example
> >
> > Swap(&a,&b);
> >
> > unsing a function
> >
> > void swap (int *px, int *py)
> > {
> > int temp;
> > temp:= *px;
> > *px = *py;
> > *py = temp
> > }[/color]
>
> You should really try hard to get your spelling correct. The code that
> you wrote has no chance of ever compiling, and even if it did, what does
> the function "swap" have to do with the function "Swap" that you are
> trying to call?[/color]

That's a fair point as code should be correct when it's posted.
[color=blue]
> I am sure that Mr. Ritchie has never written a book together with anyone
> by the name of Kerninghan. I know the word "sing" but I have no idea
> what you mean by "unsing". If you think I am too pedantic, then
> programming is not for you.[/color]

I don't think this is fair though, as the chap appears to be German, and
probably
has a certain amount of difficulty with English, it not being his native
language.
Criticism of one typographical error and one misspelling, which do not
affect comprehension of
his message, is unwarranted. If it was unreadable garbage I would agree with
you,
but it's not.

Rowland.

[Christian Bau]

Re: Pointer question

In article <ce7pm1$ea9$1@s parta.btinterne t.com>,
"Rowland" <banksr0@hotmai l.com> wrote:
[color=blue]
> "Christian Bau" <christian.bau@ cbau.freeserve. co.uk> wrote in message
> news:christian. bau-5D99B5.09123528 072004@slb-newsm1.svr.pol. co.uk...[/color]
[color=blue][color=green]
> > I am sure that Mr. Ritchie has never written a book together with anyone
> > by the name of Kerninghan. I know the word "sing" but I have no idea
> > what you mean by "unsing". If you think I am too pedantic, then
> > programming is not for you.[/color]
>
> I don't think this is fair though, as the chap appears to be German, and
> probably
> has a certain amount of difficulty with English, it not being his native
> language.
> Criticism of one typographical error and one misspelling, which do not
> affect comprehension of
> his message, is unwarranted. If it was unreadable garbage I would agree with
> you,
> but it's not.[/color]

Spelling "Kernighan" correctly has nothing to do with your native
language. And I am one hundred percent sure that there is not one German
who knows the word "using" and would believe that it is spelt as
"unsing".

[Rowland]

Re: Pointer question


"Christian Bau" <christian.bau@ cbau.freeserve. co.uk> wrote in message
news:christian. bau-E5DD3A.10202428 072004@slb-newsm1.svr.pol. co.uk...[color=blue]
> In article <ce7pm1$ea9$1@s parta.btinterne t.com>,
> "Rowland" <banksr0@hotmai l.com> wrote:
>[color=green]
> > "Christian Bau" <christian.bau@ cbau.freeserve. co.uk> wrote in message
> > news:christian. bau-5D99B5.09123528 072004@slb-newsm1.svr.pol. co.uk...[/color]
>[color=green][color=darkred]
> > > I am sure that Mr. Ritchie has never written a book together with[/color][/color][/color]
anyone[color=blue][color=green][color=darkred]
> > > by the name of Kerninghan. I know the word "sing" but I have no idea
> > > what you mean by "unsing". If you think I am too pedantic, then
> > > programming is not for you.[/color]
> >
> > I don't think this is fair though, as the chap appears to be German, and
> > probably
> > has a certain amount of difficulty with English, it not being his native
> > language.
> > Criticism of one typographical error and one misspelling, which do not
> > affect comprehension of
> > his message, is unwarranted. If it was unreadable garbage I would agree[/color][/color]
with[color=blue][color=green]
> > you,
> > but it's not.[/color]
>
> Spelling "Kernighan" correctly has nothing to do with your native
> language. And I am one hundred percent sure that there is not one German
> who knows the word "using" and would believe that it is spelt as
> "unsing".[/color]

I do agree that there is not one German. Perhaps two, or even three ("If you
think I am too pedantic, then programming is not for you." (sorry, couldn't
resist!)).

You're right in that I should have said two typos. I still feel it was a
slight over-reaction to two minor mistakes, and unhelpful to the discussion
though. I don't mean to flame, and I agree that it's a very subjective line
as to when somebodies lack of grammar/punctuation/spelling/etc. becomes a
problem. All IMHO, naturally ;-)

Warm regards,

Rowland.

[SM Ryan]

Re: Pointer question

temporary1234@q uantentunnel.de (Erik) wrote:
# Hi,
# to swap the integer variables a,b,
# in Kerninghan-Ritchie I find the function example
#
# Swap(&a,&b);
#
# unsing a function
#
# void swap (int *px, int *py)
# {
# int temp;
# temp:= *px;
# *px = *py;
# *py = temp
# }
#
# Now here I have a problem understanding that.
# The function gets two !Pointers! an arguments.
#
# So as far as I see *px=&a will happen, but *px is an integer
# variable and &a is a pointer. But I think px=&a would be
# correct.

If you're referring to the explanation of function call by inlining
the function text, what you've really got is

Swap(&a,&b);
---------------------------
{
int *px = &a;
int *py = &b;
{
int temp;
temp = *px;
*px = *py;
*py = temp
}
}

So that implied parameter assignment is equivalent to the initialiser
in a declaration, not to the assignment expression in a statement.
In a declaration, *px does not mean dereference px, but rather it
declares that px can be dereferenced in subsequent statements.

--
SM Ryan http://www.rawbw.com/~wyrmwif/
I think that's kinda of personal; I don't think I should answer that.

[Martin Ambuhl]

Re: Pointer question

Erik wrote:
[color=blue]
>
> void swap (int *px, int *py)
> {
> int temp;
> temp:= *px;
> *px = *py;
> *py = temp
> }
>
> Now here I have a problem understanding that.
> The function gets two !Pointers! an arguments.
>
> So as far as I see *px=&a will happen, but *px is an integer
> variable and &a is a pointer. But I think px=&a would be
> correct.[/color]

It is an error to think that the assignment "*px=&a will happen". 'px'
is a pointer to int, and it is px (not *px) set to &a. What you think
"would be correct" is in fact what happens.

[Martin Ambuhl]

Re: Pointer question

Christian Bau wrote:
[color=blue]
> In article <c16042a8.04072 72357.1d21584@p osting.google.c om>,
> temporary1234@q uantentunnel.de (Erik) wrote:
>
>[color=green]
>>Hi,
>>to swap the integer variables a,b,
>>in Kerninghan-Ritchie I find the function example
>>
>>Swap(&a,&b) ;
>>
>>unsing a function
>>
>>void swap (int *px, int *py)
>>{
>>int temp;
>>temp:= *px;
>>*px = *py;
>>*py = temp
>>}[/color]
>
>
> You should really try hard to get your spelling correct.[/color]

While case is important, so the mistake of 'Swap' for 'swap' matters,
the typo of 'unsing' and misspelling 'Kerningham' hardly matter.
However, the misspelling of ':=' for the assignment operator is not only
important, but suggests a background in a language from Switzerland that
does _not_ distinguish between 'Swap' and 'swap'.
[color=blue]
> The code that
> you wrote has no chance of ever compiling, and even if it did, what does
> the function "swap" have to do with the function "Swap" that you are
> trying to call?
>
> I am sure that Mr. Ritchie has never written a book together with anyone
> by the name of Kerninghan. I know the word "sing" but I have no idea
> what you mean by "unsing". If you think I am too pedantic, then
> programming is not for you.[/color]