Difference b/w storage class and storage class specifier - C

On 25 Jul 2006 10:54:46 GMT, "sarathy" <sps.sarathy@gmail.com> wrote
in comp.lang.c.moderated:

> Hi,
> What is the difference b/w a "storage class" and "storage
> class specifier"?
> It is said that there,
>
> Storage Class --> automatic static ( K&R )
> Storage Class Specifier --> auto extern register static
> typedef

C has three storage classes, not two: automatic, static, and
allocated. Allocated storage only comes from calls to the memory
management functions malloc(), calloc(), or realloc().

All objects defined in a program therefore have either automatic or
static storage duration.

All objects defined at file scope, that is outside of any function,
have static storage duration without exception.

Objects defined inside a function have automatic storage duration by
default, but they can be given static storage duration by use of the
"static" keyword in their definition. You can add the keyword "auto",
the automatic storage duration specifier, as a redundancy but it has
no effect. Any object that can have automatic storage duration has it
by default anyway. Example:

void func(void)
{
auto int a; /* a has automatic storage duration */
int b; /* but so does b, auto is default inside function */
static int c; /* c has static, not automatic, duration */
}

The register keyword specifies the register storage duration. It may
be applied to function arguments and objects defined inside a
function. It is a hint and a request to the compiler, that a
particular object might be heavily used, and a request to store it in
a machine register or other special location that might have faster
than normal access. The compiler is free to honor or ignore the
request. If you define an object with the register storage class, you
are not allowed to take its address, otherwise it is the same as the
automatic storage class.

Four of the five type specifiers do exactly that. When you use the
keyword in the definition of an object, it specifies the storage
duration that you want that object to have. Only two of them have can
actually change the default storage class of an object, static or
register on a block scope object that would otherwise have automatic
storage.

The fifth keyword, typedef, is listed as a storage class specifier, is
lumped in with the actual specifiers for convenience. If you look at
the C language grammar, or if you are writing a C compiler, you will
see that the typedef keyword can appear in a declaration with a symbol
with exactly the same syntax as a "real" storage class specifier.

> What does a specifier mean? I see the name "specifier" also
> being used in

A specifier means what its ordinary English definition would suggest,
something that specifies some feature.

> type specifier

When you define an object in C, it must have a type:

int i;
double d;

Here the int and double keywords specify the type of the objects 'i'
and 'd'.

> struct-specifier
> union-specifier

These are the terms the standard applies to the definitions or forward
declarations of struct and union types.

> etc...
>
> Regards,
> Sarathy

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://c-faq.com/
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.learn.c-c++
http://www.contrib.andrew.cmu.edu/~a...FAQ-acllc.html
--
comp.lang.c.moderated - moderation address: clcm@plethora.net -- you must
have an appropriate newsgroups line in your header for your mail to be seen,
or the newsgroup name in square brackets in the subject line. Sorry.

"sarathy" <sps.sarathy@gmail.com> writes:
> What is the difference b/w a "storage class" and "storage
> class specifier"?
[...]

This was answered in comp.lang.c over a week ago.

Posting the same question to clc and clcm is rarely a good idea. By
the time the question shows up in clcm, it will already have been
answered in clc, and probably triggered a flame war or two.

clc is good for reasonably quick answers. clcm is good for a high
signal/noise ratio.

--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
--
comp.lang.c.moderated - moderation address: clcm@plethora.net -- you must
have an appropriate newsgroups line in your header for your mail to be seen,
or the newsgroup name in square brackets in the subject line. Sorry.