C99 Question

[Vijay Kumar R Zanvar]

Hi,

Which section of C99 says that return value
of malloc(3) should not be casted?

Thanks.

--
Vijay Kumar R Zanvar
My Home Page - http://www.geocities.com/vijoeyz/

[Martin Dickopp]

"Vijay Kumar R Zanvar" <vi*****@hotpop .com> writes:

Which section of C99 says that return value
of malloc(3) should not be casted?

None. The standard only defines the language, it does not advise on
good programming style.

Martin

[Richard Heathfield]

Vijay Kumar R Zanvar wrote:

Hi,

Which section of C99 says that return value
of malloc(3) should not be casted?

The same section that says you should not microwave your cat.

Casting malloc is deprecated by the regular subscribers in this newsgroup
because:

(a) it does nothing good;
(b) it doesn't stop anything bad happening;
(c) it can (in certain circumstances in C90) actually /cause/ something bad
to happen.

Even if you're not persuaded by (a) and (b) together (which you probably
should be), (c) should be a showstopper.

The malloc function - Just Don't Cast.

--
Richard Heathfield : bi****@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

[lallous]

Hello,
"Richard Heathfield" <in*****@addres s.co.uk.invalid > wrote in message
news:3f******@n ews2.power.net. uk...

Vijay Kumar R Zanvar wrote:
The malloc function - Just Don't Cast. This might be silly from me, but you mean don't cast as:
int *i = (int *) malloc(sizeof(i nt));
?
What other solutions are there then? just assign w/o casting?

--
Richard Heathfield : bi****@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 Bos]

"Vijay Kumar R Zanvar" <vi*****@hotpop .com> wrote:

Which section of C99 says that return value
of malloc(3) should not be casted?

There is no section of C99 that says that; if there were, you wouldn't
be able to do it. It's a very bad idea all the same.
In fact, it's similar to there not being any law forbidding you to shoot
yourself in the foot. You _are_ allowed to do that; but expect it to
hurt, and do not expect your insurance to pay for the medical costs.

Richard

[Richard Heathfield]

lallous wrote:

Hello,
"Richard Heathfield" <in*****@addres s.co.uk.invalid > wrote in message
news:3f******@n ews2.power.net. uk...

Vijay Kumar R Zanvar wrote:
The malloc function - Just Don't Cast. This might be silly from me, but you mean don't cast as:
int *i = (int *) malloc(sizeof(i nt));
?

Yes, I mean that this cast is pointless and can be harmful.
What other solutions are there then? just assign w/o casting?

T *p = malloc(n * sizeof *p);

works for any object type T. You can omit n if it's 1, of course.

Your example would be better written as: int *i = malloc(sizeof *i);

--
Richard Heathfield : bi****@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

[pete]

Vijay Kumar R Zanvar wrote:

Hi,

Which section of C99 says that return value
of malloc(3) should not be casted?

How about an errata from K&R2 instead ?

142(§6.5, toward the end):
The remark about casting the return value of malloc
("the proper method is to declare ... then explicitly coerce")
needs to be rewritten. The example is correct and works,
but the advice is debatable in the context of the
1988-1989 ANSI/ISO standards. It's not necessary
(given that coercion of void * to ALMOSTANYTYPE * is automatic),
and possibly harmful if malloc,
or a proxy for it, fails to be declared as returning void *.
The explicit cast can cover up an unintended error.
On the other hand, pre-ANSI, the cast was necessary,
and it is in C++ also.

http://cm.bell-labs.com/cm/cs/cbook/2ediffs.html

--
pete

[pete]

Richard Heathfield wrote:

lallous wrote:

Hello,
"Richard Heathfield" <in*****@addres s.co.uk.invalid >
wrote in message
news:3f******@n ews2.power.net. uk...

Vijay Kumar R Zanvar wrote:
The malloc function - Just Don't Cast.

This might be silly from me, but you mean don't cast as:
int *i = (int *) malloc(sizeof(i nt));
?

Yes, I mean that this cast is pointless and can be harmful.

What other solutions are there then? just assign w/o casting?

T *p = malloc(n * sizeof *p);

works for any object type T. You can omit n if it's 1, of course.

Your example would be better written as: int *i = malloc(sizeof *i);

Neither of your posts in this thread, mention stdlib.h.
In order to write the lines that you wrote, there has to be

#include <stdlib.h>

in the code, somewhere before those lines,
otherwise the compiler will generate a warning which,
(though the warning signifies an absence of stdlib.h to us,)
may suggest a cast, and confuse the programmer into thinking
that the return value of malloc should be cast.
And who's the programmer going to believe, clc or his compiler ?

--
pete

[Richard Heathfield]

pete wrote:

Richard Heathfield wrote:

<snip>
Your example would be better written as: int *i = malloc(sizeof *i);
Neither of your posts in this thread, mention stdlib.h.

Thanks for mentioning <stdlib.h> which, of course, provides the essential
function prototype that is so critical to correct malloc usage.
And who's the programmer going to believe, clc or his compiler ?

If he is wise, he will believe clc (and then he will find out precisely
*why* his compiler is right).

--
Richard Heathfield : bi****@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

[lallous]

Hello,

"Richard Heathfield" <in*****@addres s.co.uk.invalid > wrote in message
news:3f******@n ews2.power.net. uk...

pete wrote:

Richard Heathfield wrote:

<snip>
Your example would be better written as: int *i = malloc(sizeof *i);
Neither of your posts in this thread, mention stdlib.h.

Thanks for mentioning <stdlib.h> which, of course, provides the essential
function prototype that is so critical to correct malloc usage.

And who's the programmer going to believe, clc or his compiler ?

If he is wise, he will believe clc (and then he will find out precisely
*why* his compiler is right).

I use the cast to avoid warning or when using malloc() in a C++ program.

The stdlib.h would remove the warning? How, compiler switch (like vc's
#pragma warn(disable:n) )?

--
Elias --
Richard Heathfield : bi****@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