Question on switch block scope

[Minti]

I was reading some text and I came across the following snippet

switch('5')
{
int x = 123;
case '5':
printf("The value of x %d\n", x);
break;
}
Now according to the text the memory would be allocated for the varible x but

the value of x would be an intermediate one. Can anybody expain the rationale

for this I ran this snippet [ with the obvious additions] through a C++

compiler and it gave me an error for this the following definition

int x = 123;

Is this sort of behavior of any use?

I could have better done through

{
int x = 123;
switch('5') {
....
}
}

But I was just wondering as to even declaring a variable in the switch level

scope should be allowed?

--
FUCK SCO!
Imanpreet Singh Arora
isingh AT acm DOT org
Even if you are on the right track you are going to get run over if you just
keep sitting there . - Will Rogers

[Sheldon Simms]

On Thu, 13 Nov 2003 12:26:59 -0800, Minti wrote:

I was reading some text and I came across the following snippet

switch('5')
{
int x = 123;
case '5':
printf("The value of x %d\n", x);
break;
}
Now according to the text the memory would be allocated for the varible x but
the value of x would be an intermediate one. Can anybody expain the rationale

The assignment of 123 to x never happens
The code is equivalent to:

goto foo;
{
int x = 123;
foo:
printf("The value of x %d\n", x);
}

-Sheldon

[Alan Balmer]

On Thu, 13 Nov 2003 16:20:04 -0500, Sheldon Simms
<sh**********@y ahoo.com> wrote:

On Thu, 13 Nov 2003 12:26:59 -0800, Minti wrote:

I was reading some text and I came across the following snippet

switch('5')
{
int x = 123;
case '5':
printf("The value of x %d\n", x);
break;
}
Now according to the text the memory would be allocated for the varible x but
the value of x would be an intermediate one. Can anybody expain the rationale

The assignment of 123 to x never happens
The code is equivalent to:

goto foo;
{
int x = 123;
foo:
printf("The value of x %d\n", x);
}

-Sheldon

Is this not a declaration with initialization, rather than an
assignment?

--
Al Balmer
Balmer Consulting
re************* ***********@att .net

[Eric Sosman]

Minti wrote [reformatted for better line length and spacing]:

I was reading some text and I came across the following snippet

switch('5')
{
int x = 123;
case '5':
printf("The value of x %d\n", x);
break;
}
Now according to the text the memory would be allocated for the varible x
but the value of x would be an intermediate one. Can anybody expain the
rationale for this
Which "this" do you mean? Why `x' is indeterminate,
or why the code was written this way?

The value of `x' is indeterminate because the `switch'
statement jumps directly to the selected `case' or `default'.
The executable code that sets `x' equal to 123 cannot be
reached, and thus is not executed.

The programmer's reason for attempting this construct
is a mystery I am unable to explain. Perhaps his or her
grasp of C was not very firm.
I could have better done through

{
int x = 123;
switch('5') {
....
}
}
That is fine; you have cured the indeterminacy.
But I was just wondering as to even declaring a variable in the switch
level scope should be allowed?
Variable declarations are permitted at the start of
*any* {}-enclosed executable block. There is nothing special
about `switch' in this regard.

Is the technique useful? Yes, it can be. If a block
is the only user of some particular variable, it may be
a good idea to limit the variable's scope to the block.
This can emphasize to the human reader that the variable
has no significance outside the block, and may also help
the compiler discover when the variable has "died" so it
can re-use the registers or other resources that held it.
FUCK SCO!

No; you might impregnate them and help them propagate
their genes. You are already known as someone who adds to
the load of mindless profanity under which we groan; do
you also want to become known as the father of little SCOlet?

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

[Sheldon Simms]

On Thu, 13 Nov 2003 14:31:36 -0700, Alan Balmer wrote:

On Thu, 13 Nov 2003 16:20:04 -0500, Sheldon Simms
<sh**********@y ahoo.com> wrote:

On Thu, 13 Nov 2003 12:26:59 -0800, Minti wrote:

I was reading some text and I came across the following snippet

switch('5')
{
int x = 123;
case '5':
printf("The value of x %d\n", x);
break;
}
Now according to the text the memory would be allocated for the varible x but
the value of x would be an intermediate one. Can anybody expain the rationale

The assignment of 123 to x never happens
The code is equivalent to:

goto foo;
{
int x = 123;
foo:
printf("The value of x %d\n", x);
}

-Sheldon

Is this not a declaration with initialization, rather than an
assignment?

Well yes it is, but it doesn't make a difference.

6.8#3
The initializers of objects that have automatic storage duration, ...
are evaluated and the values are stored in the objects ... each time
the declaration is reached in the order of execution, as if it were a
statement

In the examples above, the declaration is never reached and so the
variable is not initialized.

[Alan Balmer]

On Thu, 13 Nov 2003 18:13:30 -0500, Sheldon Simms
<sh**********@y ahoo.com> wrote:

Is this not a declaration with initialization, rather than an
assignment?

Well yes it is, but it doesn't make a difference.

<blushing>

Sleeping on the job. Trying to get into the OP's mindset can be
carried too far ;-)

--
Al Balmer
Balmer Consulting
re************* ***********@att .net

[sahukar praveen]

"Sheldon Simms" <sh**********@y ahoo.com> wrote in message
news:pa******** *************** **@yahoo.com...

On Thu, 13 Nov 2003 14:31:36 -0700, Alan Balmer wrote:

On Thu, 13 Nov 2003 16:20:04 -0500, Sheldon Simms
<sh**********@y ahoo.com> wrote:

On Thu, 13 Nov 2003 12:26:59 -0800, Minti wrote:

I was reading some text and I came across the following snippet

switch('5')
{
int x = 123;
case '5':
printf("The value of x %d\n", x);
break;
}
Now according to the text the memory would be allocated for the varible x but the value of x would be an intermediate one. Can anybody expain the rationale
The assignment of 123 to x never happens
The code is equivalent to:

goto foo;
{
int x = 123;
foo:
printf("The value of x %d\n", x);
}

-Sheldon

Is this not a declaration with initialization, rather than an
assignment?

Well yes it is, but it doesn't make a difference.

6.8#3
The initializers of objects that have automatic storage duration, ...
are evaluated and the values are stored in the objects ... each time
the declaration is reached in the order of execution, as if it were a
statement

In the examples above, the declaration is never reached and so the
variable is not initialized.

Hello Sheldon,

The contents below the header "6.8#3" seems to be an extract from some
standard document. Could you
please provide me more details about the document and the location where I
can get it.

Thanks and Regards,
Praveen Kumar

[Ben Pfaff]

"sahukar praveen" <sa************ @yahoo.co.in> writes:

The contents below the header "6.8#3" seems to be an extract from some
standard document. Could you
please provide me more details about the document and the location where I
can get it.

This is in the FAQ.

Section 11. ANSI/ISO Standard C

11.1: What is the "ANSI C Standard?"

A: In 1983, the American National Standards Institute (ANSI)
commissioned a committee, X3J11, to standardize the C language.
After a long, arduous process, including several widespread
public reviews, the committee's work was finally ratified as ANS
X3.159-1989 on December 14, 1989, and published in the spring of
1990. For the most part, ANSI C standardizes existing practice,
with a few additions from C++ (most notably function prototypes)
and support for multinational character sets (including the
controversial trigraph sequences). The ANSI C standard also
formalizes the C run-time library support routines.

More recently, the Standard has been adopted as an international
standard, ISO/IEC 9899:1990, and this ISO Standard replaces the
earlier X3.159 even within the United States (where it is known
as ANSI/ISO 9899-1990 [1992]). As an ISO Standard, it is
subject to ongoing revision through the release of Technical
Corrigenda and Normative Addenda.

In 1994, Technical Corrigendum 1 (TC1) amended the Standard
in about 40 places, most of them minor corrections or
clarifications, and Normative Addendum 1 (NA1) added about 50
pages of new material, mostly specifying new library functions
for internationaliz ation. In 1995, TC2 added a few more minor
corrections.

As of this writing, a complete revision of the Standard is in
its final stages. The new Standard is nicknamed "C9X" on the
assumption that it will be finished by the end of 1999. (Many
of this article's answers have been updated to reflect new C9X
features.)

The original ANSI Standard included a "Rationale, " explaining
many of its decisions, and discussing a number of subtle points,
including several of those covered here. (The Rationale was
"not part of ANSI Standard X3.159-1989, but... included for
information only," and is not included with the ISO Standard.
A new one is being prepared for C9X.)

11.2: How can I get a copy of the Standard?

A: Copies are available in the United States from

American National Standards Institute
11 W. 42nd St., 13th floor
New York, NY 10036 USA
([phone]

and

Global Engineering Documents
15 Inverness Way E
Englewood, CO 80112 USA
([phone]
[phone] (U.S. & Canada)

In other countries, contact the appropriate national standards
body, or ISO in Geneva at:

ISO Sales
Case Postale 56
CH-1211 Geneve 20
Switzerland

(or see URL http://www.iso.ch or check the comp.std.intern at FAQ
list, Standards.Faq).

The last time I checked, the cost was $130.00 from ANSI or
$400.50 from Global. Copies of the original X3.159 (including
the Rationale) may still be available at $205.00 from ANSI or
$162.50 from Global. Note that ANSI derives revenues to support
its operations from the sale of printed standards, so electronic
copies are *not* available.

In the U.S., it may be possible to get a copy of the original
ANSI X3.159 (including the Rationale) as "FIPS PUB 160" from

National Technical Information Service (NTIS)
U.S. Department of Commerce
Springfield, VA 22161
703 487 4650

The mistitled _Annotated ANSI C Standard_, with annotations by
Herbert Schildt, contains most of the text of ISO 9899; it is
published by Osborne/McGraw-Hill, ISBN 0-07-881952-0, and sells
in the U.S. for approximately $40. It has been suggested that
the price differential between this work and the official
standard reflects the value of the annotations: they are plagued
by numerous errors and omissions, and a few pages of the
Standard itself are missing. Many people on the net recommend
ignoring the annotations entirely. A review of the annotations
("annotated annotations") by Clive Feather can be found on the
web at http://www.lysator.liu.se/c/schildt.html .

The text of the Rationale (not the full Standard) can be
obtained by anonymous ftp from ftp.uu.net (see question 18.16)
in directory doc/standards/ansi/X3.159-1989, and is also
available on the web at http://www.lysator.liu.se/c/rat/title.html .
The Rationale has also been printed by Silicon Press,
ISBN 0-929306-07-4.

Public review drafts of C9X are available from ISO/IEC
JTC1/SC22/WG14's web site, http://www.dkuug.dk/JTC1/SC22/WG14/ .

See also question 11.2b below.

--
"For those who want to translate C to Pascal, it may be that a lobotomy
serves your needs better." --M. Ambuhl

"Here are the steps to create a C-to-Turbo-Pascal translator..." --H. Schildt

[CBFalconer]

Alan Balmer wrote:

.... snip ...
Is this not a declaration with initialization, rather than an
assignment?

Contrary to external appearances, there is no such declaration for
automatic variables. Code must always be generated to perform the
initialization. Which is one reason I prefer to write such code
out myself (it only requires one extra typing of the variable
name, and one extra semi, neither of which appears to create a
desperate shortage).

--
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 <3F************ ***@yahoo.com> CBFalconer <cb********@yah oo.com> writes:

Alan Balmer wrote:

... snip ...

Is this not a declaration with initialization, rather than an
assignment?

Contrary to external appearances, there is no such declaration for
automatic variables.

Of course there is:

int x;

at block scope.
Code must always be generated to perform the initialization.
Nonsense. The compiler merely has to allocate space for x on a
stack-like data structure, without touching this space. The program
can assign something to x at any time before trying to access its value
for the first time. If this something is not available at the time the
variable is defined, there is no point in providing an initialiser.
Which is one reason I prefer to write such code
out myself (it only requires one extra typing of the variable
name, and one extra semi,

???

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de