void* question

[Janice]

What is the major reason for using void*?
When should we use void* for both input arguments and return value?
How can we cast the void* pointer to the type we need?
Thanx

[Eric Sosman]

Janice wrote:

What is the major reason for using void*?
Use a `void*' when you do not know the pointed-to
object's actual type, or do not care what it is, or
wish to conceal it.
When should we use void* for both input arguments and return value?
When both the arguments and the returned value meet
one or more of the criteria above.
How can we cast the void* pointer to the type we need?

The only way to cast anything is with a cast operator.
To convert a `void*' to an `int*', say, use `(int*)voidptr' .

Perhaps if you'd give a little more detail about what's
puzzling you, I'd be able to explain more clearly.

--
Er*********@sun .com

[Ben Pfaff]

Eric Sosman <er*********@su n.com> writes:

Janice wrote:

How can we cast the void* pointer to the type we need?

The only way to cast anything is with a cast operator.
To convert a `void*' to an `int*', say, use `(int*)voidptr' .

This is literally true, but not very helpful. It is not usually
necessary to cast to or from void * because conversions between
void * and other pointers to object or incomplete type do not
require casts.
--
"Large amounts of money tend to quench any scruples I might be having."
-- Stephan Wilms

[Christopher Benson-Manica]

Eric Sosman <er*********@su n.com> spoke thus:

Perhaps if you'd give a little more detail about what's
puzzling you, I'd be able to explain more clearly.

IMHO it sounds like homework, so maybe you did just fine...

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[Eric Sosman]

Ben Pfaff wrote:

Eric Sosman <er*********@su n.com> writes:

Janice wrote:

How can we cast the void* pointer to the type we need?

The only way to cast anything is with a cast operator.
To convert a `void*' to an `int*', say, use `(int*)voidptr' .

This is literally true, but not very helpful. It is not usually
necessary to cast to or from void * because conversions between
void * and other pointers to object or incomplete type do not
require casts.

C'mon, Ben: Leave her professor *some* excuse for taking
off a mark or two, won't you?

Janice: If your questions aren't homework, I repeat my
offer to try to answer more clearly if you'll explain your
difficulty in greater detail. If they *are* homework, you
can find the answers to these and to all your other C questions
in "The Annotated ANSI C Standard" by Herbert Schildt.

--
Er*********@sun .com

[Default User]

Janice wrote:

What is the major reason for using void*?
When should we use void* for both input arguments and return value?
How can we cast the void* pointer to the type we need?

Do your own homework.


Brian

[Michael Mair]

Eric Sosman wrote:

Ben Pfaff wrote:

Eric Sosman <er*********@su n.com> writes:

Janice wrote:
How can we cast the void* pointer to the type we need?

The only way to cast anything is with a cast operator.
To convert a `void*' to an `int*', say, use `(int*)voidptr' .

This is literally true, but not very helpful. It is not usually
necessary to cast to or from void * because conversions between
void * and other pointers to object or incomplete type do not
require casts.

C'mon, Ben: Leave her professor *some* excuse for taking
off a mark or two, won't you?

Janice: If your questions aren't homework, I repeat my
offer to try to answer more clearly if you'll explain your
difficulty in greater detail. If they *are* homework, you
can find the answers to these and to all your other C questions
in "The Annotated ANSI C Standard" by Herbert Schildt.

Ouch, that hurts ;-)
I would not have thought of homework...

On the other hand, even though [ni]{2}famous, Schildt's book
costs something. I suggest reviewing the chapters 4-6 of
this newsgroup's FAQ. Start from here:
http://www.eskimo.com/~scs/C-faq/top.html
Cheers
Michael
--
E-Mail: Mine is an /at/ gmx /dot/ de address.

[CBFalconer]

Eric Sosman wrote:

Janice wrote:
.... snip ...

How can we cast the void* pointer to the type we need?

The only way to cast anything is with a cast operator.
To convert a `void*' to an `int*', say, use `(int*)voidptr' .

Er - no cast needed nor desirable. Simply assign the void* to an
int* and the conversion is automatic.

--
Chuck F (cb********@yah oo.com) (cb********@wor ldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE worldnet address!

[Dan Pop]

In <I8********@new s.boeing.com> "Default User" <fi********@boe ing.com.invalid > writes:

Janice wrote:

What is the major reason for using void*?
When should we use void* for both input arguments and return value?
How can we cast the void* pointer to the type we need?

Do your own homework.

If it's homework, it's the most stupid kind of homework I have ever seen.
These are the things that have to be taught to the student, rather than
asking him to figure them out by himself.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de
Currently looking for a job in the European Union

[Dan Pop]

In <41************ ***@yahoo.com> CBFalconer <cb********@yah oo.com> writes:

Eric Sosman wrote:

Janice wrote:

... snip ...

How can we cast the void* pointer to the type we need?

The only way to cast anything is with a cast operator.
To convert a `void*' to an `int*', say, use `(int*)voidptr' .

Er - no cast needed nor desirable. Simply assign the void* to an
int* and the conversion is automatic.

At the expense of creating an additional object. Sometimes it is worth
it, but not always.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de
Currently looking for a job in the European Union