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sheroork (in m)
said:

| Can anyone help me in getting to understand pointer to pointer with
| examples?

Sagar...

The explanations posted so far look good. These two links make up
another example of how pointers to pointers might be used:

http://www.iedu.com/mrd/c/tokenize.c
http://www.iedu.com/mrd/c/tokfile.c

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto

Morris Dovey wrote:
> sheroork (in m)
> said:
>
> | Can anyone help me in getting to understand pointer to pointer with
> | examples?
>
> Sagar...
>
> The explanations posted so far look good. These two links make up
> another example of how pointers to pointers might be used:
>
> http://www.iedu.com/mrd/c/tokenize.c
> http://www.iedu.com/mrd/c/tokfile.c

They look more like an example of how not to write C to me.

Rather than having a tokenize.h containing the prototype for the
tokenize function it has the prototype repeated in tokfile.c. So you
have to maintain it in two places with no help from the compiler.

Using a file scope variable for the function to determine if a character
is a word separator or part of a word instead of passing it down. What
is worse, a single character name for it!

Assuming ASCII or similar character encoding instead of using the
portable standard is* functions.

Increasing the hard to follow coupling by using another file scope
variable s to hold a pointer to the character being processed. The
author seems to have a major objection to using parameters!

Using recursion for what could more simply be implemented with a for
loop, and the state being passed down via the afore mentioned file scope
variables instead of parameters!

That code is so needlessly convoluted that pointing a beginner at it is
tantamount to cruelty!
--
Flash Gordon
Still sigless on this computer.

Thanks friends for all your time and knowledge you have posted.
I will be greatful for your postings.

Thanks,
Sagar

August Karlstrom wrote:
> sheroork wrote:
> > Can anyone help me in getting to understand pointer to pointer with
> > examples?
>
> int **p;
>
> p
> +---+
> | ? |
> +---+
>
> p = malloc(sizeof *p);
>
> p *p
> +---+ +---+
> | ----->| ? |
> +---+ +---+
>
> *p = malloc(sizeof **p);
>
> p *p **p
> +---+ +---+ +---+
> | ----->| ----->| ? |
> +---+ +---+ +---+
>
> **p = 7;
>
> p *p **p
> +---+ +---+ +---+
> | ----->| ----->| 7 |
> +---+ +---+ +---+

I, for one, welcome our ASCII art overlords.

Tom

Richard Heathfield wrote:

> Scorpio said:

> > Sorry, I was mistaken and yes, August's code is correct.
> > But I actually meant: *p=malloc(sizeof(int));
> > Is something wrong with this?
>
> It will at least compile, but it's inferior to August's version,
> because you're nailing the type to the call, possibly causing a
> maintenance headache further down the line.


After all, we just got done diagnosing an incorrect malloc call in
another thread. The deference the target method isn't fool-proof, of
course, but it's closer. You still have the cut and paste problem, but
it's a tad more recognizable because you have the two variable names on
the same line, whereas the types are often widely separated.



Brian