constant in C

constant in C

[Ankit Jain]

what is the size of the constant 

i.e #define const 123456789

thanks

ankit

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Re: constant in C

[Andrei Bunghez]

Hi,

Actually that 'const' has no size at all, it is not a variable, has no
address. The preprocessor replaces  const in the source code with
123456789, or whatever its definition is.

For example:

x = const +  3;

will be preprocessed, and the compiler will see:
x = 123456789 + 3;

Therefore you cannot use sizeof(const),  &const etc.


Regards,
Andrei


On Fri, 24 Sep 2004 04:36:46 +0100 (BST), Ankit Jain
<ankitjain1580@yahoo.com> wrote:
> what is the size of the constant
> 
> i.e #define const 123456789
> 
> thanks
> 
> ankit
> 
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Fwd: constant in C

[Uday Karan]

Sorry didn't CC to list.

> Therefore you cannot use sizeof(const),  &const etc.

sizeof (CONST) can be done and would return the size of an integral
type that would be able to hold that value, could be 4 for ints or 8
for long ints, if none of these can take up the value (because you're
substitutive constant is insanely large), the compiler would usually
give out a warning (if truncating) or an error straightaway.

- Uday

Re: Fwd: constant in C

[Micha Feigin]

On Fri, Sep 24, 2004 at 01:03:17PM +0530, Uday Karan wrote:
> Sorry didn't CC to list.
> 
> > Therefore you cannot use sizeof(const),  &const etc.
> 
> sizeof (CONST) can be done and would return the size of an integral
> type that would be able to hold that value, could be 4 for ints or 8
> for long ints, if none of these can take up the value (because you're

Actually the size of long int is 4 and the size of short is 2, the size
of int depends on the platform. With the old 16bit platforms (if you
can still find them ;-) it was 2 and with 32 bit machines its 4.

Int was supposed to be a word, but on 64bit machines that is not longer
stable.

with 64bits, a pointer is of size 8, but int and long can be either 4
or 8 and sometimes there is long long.

have look at http://en.wikipedia.org/wiki/64-bit.

> substitutive constant is insanely large), the compiler would usually
> give out a warning (if truncating) or an error straightaway.
> 
> - Uday
> -
> To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
> the body of a message to majordomo@vger.kernel.org
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>  +++++++++++++++++++++++++++++++++++++++++++
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Re: Fwd: constant in C

[Ankit Jain]

can the size be greater than 4byte on a 32 bit system?

thanks

ankit
 --- Micha Feigin <michf@post.tau.ac.il> wrote: 
> On Fri, Sep 24, 2004 at 01:03:17PM +0530, Uday Karan
> wrote:
> > Sorry didn't CC to list.
> > 
> > > Therefore you cannot use sizeof(const),  &const
> etc.
> > 
> > sizeof (CONST) can be done and would return the
> size of an integral
> > type that would be able to hold that value, could
> be 4 for ints or 8
> > for long ints, if none of these can take up the
> value (because you're
> 
> Actually the size of long int is 4 and the size of
> short is 2, the size
> of int depends on the platform. With the old 16bit
> platforms (if you
> can still find them ;-) it was 2 and with 32 bit
> machines its 4.
> 
> Int was supposed to be a word, but on 64bit machines
> that is not longer
> stable.
> 
> with 64bits, a pointer is of size 8, but int and
> long can be either 4
> or 8 and sometimes there is long long.
> 
> have look at http://en.wikipedia.org/wiki/64-bit.
> 
> > substitutive constant is insanely large), the
> compiler would usually
> > give out a warning (if truncating) or an error
> straightaway.
> > 
> > - Uday
> > -
> > To unsubscribe from this list: send the line
> "unsubscribe linux-c-programming" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at 
> http://vger.kernel.org/majordomo-info.html
> >  
> >  +++++++++++++++++++++++++++++++++++++++++++
> >  This Mail Was Scanned By Mail-seCure System
> >  at the Tel-Aviv University CC.
> > 
> -
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Re: Fwd: constant in C

[Micha Feigin]

On Fri, Sep 24, 2004 at 11:47:13AM +0100, Ankit Jain wrote:
> can the size be greater than 4byte on a 32 bit system?
> 
> thanks
> 

I am not sure if long long support (yes, two longs) is completely
standard, but on compilers where it is supported its size should be 8
bytes (64 bit).

I just tested under gcc 3.3 and it is supported with it and of size 8.

> ankit
>  --- Micha Feigin <michf@post.tau.ac.il> wrote: 
> > On Fri, Sep 24, 2004 at 01:03:17PM +0530, Uday Karan
> > wrote:
> > > Sorry didn't CC to list.
> > > 
> > > > Therefore you cannot use sizeof(const),  &const
> > etc.
> > > 
> > > sizeof (CONST) can be done and would return the
> > size of an integral
> > > type that would be able to hold that value, could
> > be 4 for ints or 8
> > > for long ints, if none of these can take up the
> > value (because you're
> > 
> > Actually the size of long int is 4 and the size of
> > short is 2, the size
> > of int depends on the platform. With the old 16bit
> > platforms (if you
> > can still find them ;-) it was 2 and with 32 bit
> > machines its 4.
> > 
> > Int was supposed to be a word, but on 64bit machines
> > that is not longer
> > stable.
> > 
> > with 64bits, a pointer is of size 8, but int and
> > long can be either 4
> > or 8 and sometimes there is long long.
> > 
> > have look at http://en.wikipedia.org/wiki/64-bit.
> > 
> > > substitutive constant is insanely large), the
> > compiler would usually
> > > give out a warning (if truncating) or an error
> > straightaway.
> > > 
> > > - Uday
> > > -
> > > To unsubscribe from this list: send the line
> > "unsubscribe linux-c-programming" in
> > > the body of a message to majordomo@vger.kernel.org
> > > More majordomo info at 
> > http://vger.kernel.org/majordomo-info.html
> > >  
> > >  +++++++++++++++++++++++++++++++++++++++++++
> > >  This Mail Was Scanned By Mail-seCure System
> > >  at the Tel-Aviv University CC.
> > > 
> > -
> > To unsubscribe from this list: send the line
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> >  
> 
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Re: constant in C

[Andrei Bunghez]

Hmm.. actually you can use sizeof(const), and it returns 4, as
123456789 is a unsigned int constant.

Andrei


On Fri, 24 Sep 2004 04:36:46 +0100 (BST), Ankit Jain
<ankitjain1580@yahoo.com> wrote:
> what is the size of the constant
> 
> i.e #define const 123456789
> 
> thanks
> 
> ankit
> 
> ________________________________________________________________________
> Yahoo! Messenger - Communicate instantly..."Ping"
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