switch { } - case for range

**Ben Pfaff** · Sep 6 '06, 05:35 PM

Re: switch { } - case for range

"markpapada kis" <markpapadakis@ gmail.comwrites :

I was checking out the C-FAQ and read here (
http://c-faq.com/misc/nonconstcase.html ) that:
" case labels are limited to single, constant, integral expression ".
>
However, I have been using case with ranges for a long while ( gcc,
VC++) so either the FAQ calls for an update or those two compilers
provide this functionality as an extension.

It's an extension.
--
Go not to Usenet for counsel, for they will say both no and yes.

**BRG** · Sep 6 '06, 05:45 PM

Re: switch { } - case for range

markpapadakis wrote:

I was checking out the C-FAQ and read here (
http://c-faq.com/misc/nonconstcase.html ) that:
" case labels are limited to single, constant, integral expression ".
>
However, I have been using case with ranges for a long while ( gcc,
VC++) so either the FAQ calls for an update or those two compilers
provide this functionality as an extension.
>
example;
switch (a)
{
case 1 ... 10:
// code
break;
>
case 11 ... 50:
// code
break;
>
case 800:
// code
break;
>
default:
// code
break;
}

This doesn't work with VC++ version 8 and I don't recall it working on
earlier versions either.

Brian Gladman

**Robert Gamble** · Sep 6 '06, 05:45 PM

Re: switch { } - case for range

markpapadakis wrote:

I was checking out the C-FAQ and read here (
http://c-faq.com/misc/nonconstcase.html ) that:
" case labels are limited to single, constant, integral expression ".
>
However, I have been using case with ranges for a long while ( gcc,
VC++) so either the FAQ calls for an update or those two compilers
provide this functionality as an extension.

[snip example]

C doesn't have ranges. What you describe is an extension, one which is
clearly documented as such in the gcc documentation. What version of
VC++ are you using that allows this?

Robert Gamble

**markpapadakis** · Sep 6 '06, 05:55 PM

Re: switch { } - case for range

Robert Gamble wrote:

markpapadakis wrote:

I was checking out the C-FAQ and read here (
http://c-faq.com/misc/nonconstcase.html ) that:
" case labels are limited to single, constant, integral expression ".

However, I have been using case with ranges for a long while ( gcc,
VC++) so either the FAQ calls for an update or those two compilers
provide this functionality as an extension.

>
[snip example]
>
C doesn't have ranges. What you describe is an extension, one which is
clearly documented as such in the gcc documentation. What version of
VC++ are you using that allows this?
>
Robert Gamble

I was wrong. It does not work with VC++. It has been a long while since
I used it and I thought it was supported there as well.

Thank you for the answer to the question.

**Clark S. Cox III** · Sep 6 '06, 06:05 PM

Re: switch { } - case for range

markpapadakis wrote:

I was checking out the C-FAQ and read here (
http://c-faq.com/misc/nonconstcase.html ) that:
" case labels are limited to single, constant, integral expression ".
>
However, I have been using case with ranges for a long while ( gcc,
VC++) so either the FAQ calls for an update or those two compilers
provide this functionality as an extension.

It's an extension.

--
Clark S. Cox III
clarkcox3@gmail .com

**jacob navia** · Sep 6 '06, 07:55 PM

Re: switch { } - case for range

markpapadakis wrote:

I was checking out the C-FAQ and read here (
http://c-faq.com/misc/nonconstcase.html ) that:
" case labels are limited to single, constant, integral expression ".
>
However, I have been using case with ranges for a long while ( gcc,
VC++) so either the FAQ calls for an update or those two compilers
provide this functionality as an extension.
>
example;
switch (a)
{
case 1 ... 10:
// code
break;
>
case 11 ... 50:
// code
break;
>
case 800:
// code
break;
>
default:
// code
break;
}
>

What is your experience with this extension?

Is it really useful?

How many times did you use it?

I would be interested in knowing if it makjes sense to
implement it in lcc-win32.

jacob

**Mark McIntyre** · Sep 6 '06, 09:25 PM

Re: switch { } - case for range

On Wed, 06 Sep 2006 22:09:45 +0200, in comp.lang.c , jacob navia
<jacob@jacob.re mcomp.frwrote:

>markpapadaki s wrote:

>switch (a)
>{
>>

>
>What is your experience with this extension?

For what its worth, my experience is that its really useful if you're
a Visual Basic programmer trying to write C in the style of VB.

For myself I consider this A Very Bad Idea (tm), never ever try to use
one language in the idiom of another. Consider the early editions of
Num Rec in C as a classic case-study. I mean, why buy a scooter to
haul logs?

--
Mark McIntyre

"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
--Brian Kernighan

**markpapadakis** · Sep 6 '06, 09:25 PM

Re: switch { } - case for range

jacob navia wrote:

markpapadakis wrote:

I was checking out the C-FAQ and read here (
http://c-faq.com/misc/nonconstcase.html ) that:
" case labels are limited to single, constant, integral expression ".

However, I have been using case with ranges for a long while ( gcc,
VC++) so either the FAQ calls for an update or those two compilers
provide this functionality as an extension.

example;
switch (a)
{
case 1 ... 10:
// code
break;

case 11 ... 50:
// code
break;

case 800:
// code
break;

default:
// code
break;
}

>
What is your experience with this extension?
>
Is it really useful?
>
How many times did you use it?
>
I would be interested in knowing if it makjes sense to
implement it in lcc-win32.
>
jacob

I am using it quite often. Its useful it eliminates the need for
conditional statements ( wherever conditional statements can be used,
of course ) , provides for easier to manage/understand code and perhaps
reaps any performance benefits versus conditional statements.

Mark

**CBFalconer** · Sep 7 '06, 04:05 AM

Re: switch { } - case for range

markpapadakis wrote:

jacob navia wrote:

>markpapadaki s wrote:
>>

>>I was checking out the C-FAQ and read here (
>>http://c-faq.com/misc/nonconstcase.html ) that:
>>" case labels are limited to single, constant, integral
>>expression ".
>>>
>>However, I have been using case with ranges for a long while
>>( gcc, VC++) so either the FAQ calls for an update or those
>>two compilers provide this functionality as an extension.
>>>
>>example;
>>switch (a)
>>{
>> case 1 ... 10:
>> // code
>> break;
>>>
>> case 11 ... 50:
>> // code
>> break;
>>>
>> case 800:
>> // code
>> break;
>>>
>> default:
>> // code
>> break;
>>}

>>
>What is your experience with this extension?
>>
>Is it really useful?
>>
>How many times did you use it?
>>
>I would be interested in knowing if it makjes sense to
>implement it in lcc-win32.

>
I am using it quite often. Its useful it eliminates the need for
conditional statements ( wherever conditional statements can be
used, of course ) , provides for easier to manage/understand code
and perhaps reaps any performance benefits versus conditional
statements.

Why in heavens name use it and become non-portable, when the
portable code (following) is clearer:

if ((a >= 1) && (a <= 10)) firstcode();
else if ((a 10) && (a <= 50)) secondcode();
else if (a == 800) thirdcode();
else defaultcode();

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net>

**Richard Tobin** · Sep 7 '06, 11:55 AM

Re: switch { } - case for range

In article <44FF9701.4DF36 538@yahoo.com>,
CBFalconer <cbfalconer@mai neline.netwrote :

>Why in heavens name use it and become non-portable, when the
>portable code (following) is clearer:
>
if ((a >= 1) && (a <= 10)) firstcode();
else if ((a 10) && (a <= 50)) secondcode();
else if (a == 800) thirdcode();
else defaultcode();

That's fine in that case, but I have often had cases where there are a
few large ranges and lots of single cases (e.g. when considering a
character during the parsing of some expression). Of course you can
split it into some tests followed by a switch, but ranges would be
neater and allow the compiler to choose the most efficient set of
comparisons.

-- Richard

**Eric Sosman** · Sep 7 '06, 04:15 PM

Re: switch { } - case for range

Richard Tobin wrote On 09/07/06 08:01,:

In article <44FF9701.4DF36 538@yahoo.com>,
CBFalconer <cbfalconer@mai neline.netwrote :
>
>

>>Why in heavens name use it and become non-portable, when the
>>portable code (following) is clearer:
>>
> if ((a >= 1) && (a <= 10)) firstcode();
> else if ((a 10) && (a <= 50)) secondcode();
> else if (a == 800) thirdcode();
> else defaultcode();

>
>
That's fine in that case, but I have often had cases where there are a
few large ranges and lots of single cases (e.g. when considering a
character during the parsing of some expression). Of course you can
split it into some tests followed by a switch, but ranges would be
neater and allow the compiler to choose the most efficient set of
comparisons.

Are you looking for

case 'a' ... 'z':
case 'A' ... 'Z':
process_alphabe tic(ch);
break;

? If so, CBF's solution (now using isalpha() in a test)
is superior on several grounds, correctness among them.

--
Eric.Sosman@sun .com

**Richard Tobin** · Sep 7 '06, 06:05 PM

Re: switch { } - case for range

In article <1157646365.318 129@news1nwk>,
Eric Sosman <Eric.Sosman@su n.comwrote:

Are you looking for
>
> case 'a' ... 'z':
> case 'A' ... 'Z':
> process_alphabe tic(ch);
> break;

Something not unlike that, but I generally have Unicode values.

>? If so, CBF's solution (now using isalpha() in a test)
>is superior on several grounds, correctness among them.

Presumably you are referring to the possibility of a system where the
alphabetic characters are not consecutive, but on such a system
isalpha() would not give the right results for my Unicode characters -
I would have to use numeric ranges.

-- Richard

**Mark McIntyre** · Sep 7 '06, 08:15 PM

Re: switch { } - case for range

On 7 Sep 2006 12:01:14 GMT, in comp.lang.c , richard@cogsci. ed.ac.uk
(Richard Tobin) wrote:

>In article <44FF9701.4DF36 538@yahoo.com>,
>CBFalconer <cbfalconer@mai neline.netwrote :
>

>>Why in heavens name use it and become non-portable, when the
>>portable code (following) is clearer:
>>
> if ((a >= 1) && (a <= 10)) firstcode();
> else if ((a 10) && (a <= 50)) secondcode();
> else if (a == 800) thirdcode();
> else defaultcode();

>
>That's fine in that case, but I have often had cases where there are a
>few large ranges and lots of single cases (e.g. when considering a
>character during the parsing of some expression). Of course you can
>split it into some tests followed by a switch, but ranges would be
>neater and allow the compiler to choose the most efficient set of
>comparisons.

I would submit that the algo was probably flawed, if you found
yourself in this situation.
--
Mark McIntyre

"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
--Brian Kernighan

**Richard Tobin** · Sep 7 '06, 09:55 PM

Re: switch { } - case for range

In article <8qv0g21qf8i9vn usjrgd72rdh8sco udovu@4ax.com>,
Mark McIntyre <markmcintyre@s pamcop.netwrote :

>>That's fine in that case, but I have often had cases where there are a
>>few large ranges and lots of single cases (e.g. when considering a
>>character during the parsing of some expression). Of course you can
>>split it into some tests followed by a switch, but ranges would be
>>neater and allow the compiler to choose the most efficient set of
>>comparisons .

>I would submit that the algo was probably flawed, if you found
>yourself in this situation.

Why is that?

Here's an example. I want to classify Unicode characters according
to whether they are XML 1.1 name characters, name start characters, or
other. What is wrong with writing something like:

/* See http://www.w3.org/TR/xml11/#NT-NameStartChar */
switch(c)
{
case 0x3a: /* colon */
case 0x41...0x5a: /* A-Z */
case 0x5f: /* underscore */
case 0x61...0x7a: /* a-z */
case 0xC0...0xD6:
case 0xD8...0xF6:
case 0xF8...0x2FF:
case 0x370...0x37D:
case 0x37F...0x1FFF:
case 0x200C...0x200D :
case 0x2070...0x218F :
case 0x2C00...0x2FEF :
case 0x3001...0xD7FF :
case 0xF900...0xFDCF :
case 0xFDF0...0xFFFD :
case 0x10000...0xEFF F:
return NameStart;
case 0x2d: /* hyphen */
case 0x2e: /* full stop */
case 0x30...0x39: /* 0-9 */
case 0xb7:
case 0x300...0x36f:
case 0x203f...0x2040 :
return NameChar;
default:
return Other;
}

Obviously there are other ways to do it, but I don't see why this way
(which directly reflects the standard it is implementing) is "flawed".

-- Richard

switch { } - case for range

switch { } - case for range

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