"Continue" usage

**Richard Heathfield** · Sep 22 '08, 03:35 AM

Re: "Continue& quot; usage

mdh said:

May I ask the group this somewhat non-focused question....hav ing now
seen "continue" used in some of the solutions I have worked on. ( Ex
7-4 solution by Tondo and Gimpel comes to mind)
Is there a good principle/s for the good usage of "continue"...or ...do
any of the regular/irregular contributors have a "favorite" way in
which it is particularly useful. Thanks as usual.

Personally, I prefer to reserve it as an indicator that an otherwise empty
loop is intended to be empty:

for(t = s; *s != '\0'; (*s != c) ? *t++ = *s++ : *s++)
{
continue;
}
*t = '\0';

Another reasonable view is that it should be used for quickly dispensing
with exceptional situations encountered in a loop where you don't want to
do any processing on this iteration (but don't want to stop the loop):

while(line_read ing_function(&l ine, &len, fp) != EOF)
{
skipwhite(&line );
if(line[0] == '\0')
{
continue; /* empty line */
}
if(line[0] == '#')
{
continue; /* comment encountered */
}

/* now we can get on with processing "real" lines */

**mdh** · Sep 22 '08, 03:55 AM

Re: "Continue& quot; usage

On Sep 21, 8:39 pm, Richard Heathfield <r...@see.sig.i nvalidwrote:

mdh said:
>

May I ask the group

.....having now

seen "continue" used
Is there a good principle/s for the good usage of "continue"...or ...do
any of the regular/irregular contributors have a "favorite" way in
which it is particularly useful.

>
Personally, I prefer to reserve it as an indicator that an otherwise empty
loop is intended to be empty:
>
for(t = s; *s != '\0'; (*s != c) ? *t++ = *s++ : *s++)
{
continue;}
>
*t = '\0';
>
Another reasonable view is that it should be used for quickly dispensing
with exceptional situations encountered in a loop where you don't want to
do any processing on this iteration (but don't want to stop the loop):
>
while(line_read ing_function(&l ine, &len, fp) != EOF)
{
skipwhite(&line );
if(line[0] == '\0')
{
continue; /* empty line */
}
if(line[0] == '#')
{
continue; /* comment encountered */
}
>
/* now we can get on with processing "real" lines */
.

thanks Richard for those "hooks" to hang that idea on.

**CBFalconer** · Sep 22 '08, 08:15 AM

Re: "Continue& quot; usage

mdh wrote:

>
May I ask the group this somewhat non-focused question....hav ing
now seen "continue" used in some of the solutions I have worked
on. ( Ex 7-4 solution by Tondo and Gimpel comes to mind). Is
there a good principle/s for the good usage of "continue" or do
any of the regular/irregular contributors have a "favorite" way
in which it is particularly useful. Thanks as usual.

I primarily use it to indicate an empty statement. It is not
limited to that however. For example:

while ((EOF != (ch = getc(f))) && ('\n' != ch)) continue;

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.

**Richard Heathfield** · Sep 22 '08, 08:35 AM

Re: "Continue& quot; usage

CBFalconer said:

mdh wrote:

>>
>May I ask the group this somewhat non-focused question....hav ing
>now seen "continue" used in some of the solutions I have worked
>on. ( Ex 7-4 solution by Tondo and Gimpel comes to mind). Is
>there a good principle/s for the good usage of "continue" or do
>any of the regular/irregular contributors have a "favorite" way
>in which it is particularly useful. Thanks as usual.

>
I primarily use it to indicate an empty statement. It is not
limited to that however. For example:
>
while ((EOF != (ch = getc(f))) && ('\n' != ch)) continue;

Your example is fine, but your description is not, because you can't always
use continue to indicate an empty statement - *only* in loop contexts and
*only* where your intent is for the loop to continue from the
loop-continuation portion of the smallest enclosing iteration statement.
For example:

int main(void)
{
continue;
return 0;
}

is a constraint violation requiring a diagnostic message. Furthermore, the
following example illustrates *legal* C where the use of continue to
indicate a null statement gives the wrong code for the job:

#include <stdio.h>

int main(void)
{
int ch;
while((ch = getchar()) != EOF)
{
if(isalpha(ch))
{
if(ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u')
{
continue; /* bad idea */
}
else
{
/* consonant-specific processing - non-aeiou */
}
/* letter-specific processing - for all a-z */
}
}
return 0;
}

In this code, vowels will *not* receive letter-specific processing.

So no, using it to indicate an empty statement is not a good idea. Using it
to indicate an empty loop body is obviously fine, however.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

**Chris Dollin** · Sep 22 '08, 09:55 AM

Re: "Continue& quot; usage

mdh wrote:

May I ask the group this somewhat non-focused question....hav ing now
seen "continue" used in some of the solutions I have worked on. ( Ex
7-4 solution by Tondo and Gimpel comes to mind)
Is there a good principle/s for the good usage of "continue"...or ...do
any of the regular/irregular contributors have a "favorite" way in
which it is particularly useful. Thanks as usual.

I have seen `continue` used sensibly [1] so rarely
that I treat any use of it
as a code smell
suggesting
that there is an opportunity
to fix the design
in a way that eliminates any need
to consider continue for that code.

To indicate an empty loop body
I find `{}` perfectly adequate
on those odd occasions
when it is needed.

Mind the gap.

[1] From my POV, natch.

--
'It changed the future .. and it changed us.' /Babylon 5/

Hewlett-Packard Limited registered office: Cain Road, Bracknell,
registered no: 690597 England Berks RG12 1HN

**Richard Tobin** · Sep 22 '08, 11:35 AM

Re: "Continue& quot; usage

In article <f4udnSP9FqvLxU rVnZ2dnUVZ8qPin Z2d@bt.com>,
Richard Heathfield <rjh@see.sig.in validwrote:

>Your example is fine, but your description is not, because you can't always
>use continue to indicate an empty statement - *only* in loop contexts and
>*only* where your intent is for the loop to continue from the
>loop-continuation portion of the smallest enclosing iteration statement.

Unlike Fortran, where CONTINUE was a no-op, and was often used at the
end of loops because it could reliably be used to hang the line number
on.

-- Richard
--
Please remember to mention me / in tapes you leave behind.

**Richard** · Sep 22 '08, 11:35 AM

Re: "Continue& quot; usage

Chris Dollin <chris.dollin@h p.comwrites:

mdh wrote:
>

>May I ask the group this somewhat non-focused question....hav ing now
>seen "continue" used in some of the solutions I have worked on. ( Ex
>7-4 solution by Tondo and Gimpel comes to mind)
>Is there a good principle/s for the good usage of "continue"...or ...do
>any of the regular/irregular contributors have a "favorite" way in
>which it is particularly useful. Thanks as usual.

>
I have seen `continue` used sensibly [1] so rarely
that I treat any use of it
as a code smell
suggesting
that there is an opportunity
to fix the design
in a way that eliminates any need
to consider continue for that code.
>
To indicate an empty loop body
I find `{}` perfectly adequate
on those odd occasions
when it is needed.
>
Mind the gap.
>
[1] From my POV, natch.

Actually it makes perfect sense when you have your gate condition at the
top of the section - far easier to read, understand and maintain in many
cases (not all of course).

while(n--){

if(complexCondi tionNotMatched( n))
continue; /* not interested. Check the next if there is one. */

/*do processing of things we are interested in*/

}

Now we could invert the test but then we need to scroll down to the end
of the function to be see what else happens after the block. Here we see
that nothing happens at all - we must move to the next element.

Seems clear, maintainable and decent design to me. I fail to see how it
could be construed as "bad" in any shape or form.

**Eric Sosman** · Sep 22 '08, 12:15 PM

Re: "Continue& quot; usage

mdh wrote:

May I ask the group this somewhat non-focused question....hav ing now
seen "continue" used in some of the solutions I have worked on. ( Ex
7-4 solution by Tondo and Gimpel comes to mind)
Is there a good principle/s for the good usage of "continue"...or ...do
any of the regular/irregular contributors have a "favorite" way in
which it is particularly useful. Thanks as usual.

Hi, my name is Eric, and I'm a `continue' abuser. I use
it as a disguised `goto', simply to avoid excessive nesting:

for (...) {
... prepare for a test ...
if (not_applicable )
continue;
... prepare another test ...
if (not_applicable _2)
continue;
... payload ...
}

Inverting the sense of the tests would eliminate my abusive
`continue' statements:

for (...) {
... prepare for a test ...
if (! not_applicable) {
... prepare another test ...
if (! not_applicable_ 2) {
... payload ...
}
}
}

.... but if there are three or four such tests, as often
happens when you're converting and validating input from
an uncontrolled source, the "payload" -- the real purpose
of the function --
tends to get squee-
zed into short
little lines all
crowded at the right-
hand side and larded
with ugly line bre-
aks.

So although I know in my heart of hearts that I overuse
`continue' and really shouldn't, the way I really shouldn't
drink and smoke and gamble on cockfights, I, er, continue in
my disgusting habit. There, I've admitted my guilty secret.
They say it's the first step to recovery, but only time will
tell.

--
Eric Sosman
esosman@ieee-dot-org.invalid

**Ben Bacarisse** · Sep 22 '08, 12:55 PM

Re: "Continue& quot; usage

Richard<rgrdev@ gmail.comwrites :

Chris Dollin <chris.dollin@h p.comwrites:
>

>mdh wrote:
>>

>>May I ask the group this somewhat non-focused question....hav ing now
>>seen "continue" used in some of the solutions I have worked on.

<snip>

>I have seen `continue` used sensibly [1] so rarely
>that I treat any use of it
>as a code smell
>suggesting
>that there is an opportunity
>to fix the design

<snip>

>[1] From my POV, natch.

>
Actually it makes perfect sense when you have your gate condition at the
top of the section - far easier to read, understand and maintain in many
cases (not all of course).
>
while(n--){
>
if(complexCondi tionNotMatched( n))
continue; /* not interested. Check the next if there is one. */
>
/*do processing of things we are interested in*/
>
}
>
Now we could invert the test but then we need to scroll down to the end
of the function

You mean "loop" presumably here.

to be see what else happens after the block. Here we see
that nothing happens at all - we must move to the next element.

There is, of course, no need to invert the test though many people
really seem to object to an empty if branch -- an empty else is fine
but an empty if seems to be OTT for most people.

It is unfortunate that your example is already negative because, to my
mind, there is slightly more clarity in:

while (n--) {
if (complexConditi onMatched(n)) {
}
}

but that is just an accident of choosing a negative condition to start
with.

Seems clear, maintainable and decent design to me. I fail to see how it
could be construed as "bad" in any shape or form.

Clear and decent yes, but not 100% maintainable because you loose a
place to put code executed at the end of every loop. I honestly don't
know if this matters (I have no metric for maintainability ) but people
site less complex matters are being an issue for maintainability so I
will suggest this one.

I almost never use continue but I don't think this is because I want
to write super maintainable code, just that to me the "if in a loop"
form seems to say what I mean more clearly in all the cases that have
come up.

--
Ben.

**mdh** · Sep 22 '08, 12:55 PM

Re: "Continue& quot; usage

On Sep 22, 5:11 am, Eric Sosman <esos...@ieee-dot-org.invalidwrot e:

>
Hi, my name is Eric, and I'm a `continue' abuser.

LOL...

Thanks Eric and all who replied. More hooks to hang my ideas on. Much
Appreciated.

**Richard** · Sep 22 '08, 01:05 PM

Re: "Continue& quot; usage

Richard<rgrdev@ gmail.comwrites :

Ben Bacarisse <ben.usenet@bsb .me.ukwrites:
>

>Richard<rgrdev @gmail.comwrite s:
>>

>>Chris Dollin <chris.dollin@h p.comwrites:
>>>
>>>mdh wrote:
>>>>
>>>>May I ask the group this somewhat non-focused question....hav ing now
>>>>seen "continue" used in some of the solutions I have worked on.

><snip>

>>>I have seen `continue` used sensibly [1] so rarely
>>>that I treat any use of it
>>>as a code smell
>>>suggesting
>>>that there is an opportunity
>>>to fix the design

><snip>

>>>[1] From my POV, natch.
>>>
>>Actually it makes perfect sense when you have your gate condition at the
>>top of the section - far easier to read, understand and maintain in many
>>cases (not all of course).
>>>
>>while(n--){
>>>
>> if(complexCondi tionNotMatched( n))
>> continue; /* not interested. Check the next if there is one. */
>>>
>> /*do processing of things we are interested in*/
>>>
>>}
>>>
>>Now we could invert the test but then we need to scroll down to the end
>>of the function

>>
>You mean "loop" presumably here.

>
Of course. thanks.

Actually I was too hasty to accept your correction. No. I did not mean
loop. I meant the scope of the if block.

e.g

if(match(n){
something();
}else{
somethingelse() ;
}

here without the continue "in your face" one must check for the else at
the end when reading the code.

This

if(complexCondi tionNotMatched( n))
continue; /* not interested. Check the next if there is one. */

something();

is much more explicit and clearer.

**Ben Bacarisse** · Sep 22 '08, 01:05 PM

Re: "Continue& quot; usage

Eric Sosman <esosman@ieee-dot-org.invalidwrit es:

mdh wrote:

>May I ask the group this somewhat non-focused question....hav ing now
>seen "continue" used in some of the solutions I have worked on.

<snip>

Hi, my name is Eric, and I'm a `continue' abuser. I use
it as a disguised `goto', simply to avoid excessive nesting:

<fx:stands up>
Hello, my name is Ben, and *I* abuse break. Ah, it feels so good to
say it out loud!

I never get tempted by continue (see elsethread) but I can't keep my
hands off that lovely break. It is sooooo tempting, when you are all
hot and bothered, tightly bound by a strict loop invariant, just to
slip in little break and be free.

[Serious point: in some ways, break is much worse than continue
because of what happens to the way you think about your loops, but I
find myself using break much more than continue and paying the extra
thinking costs later because I do try to verify the logic of all my
loops.]

--
Ben.

**Chris Dollin** · Sep 22 '08, 01:05 PM

Re: "Continue& quot; usage

Richard wrote:

Chris Dollin <chris.dollin@h p.comwrites:
>

>mdh wrote:
>>

>>May I ask the group this somewhat non-focused question....hav ing now
>>seen "continue" used in some of the solutions I have worked on. ( Ex
>>7-4 solution by Tondo and Gimpel comes to mind)
>>Is there a good principle/s for the good usage of "continue"...or ...do
>>any of the regular/irregular contributors have a "favorite" way in
>>which it is particularly useful. Thanks as usual.

>>
>I have seen `continue` used sensibly [1] so rarely
>that I treat any use of it
>as a code smell
>suggesting
>that there is an opportunity
>to fix the design
>in a way that eliminates any need
>to consider continue for that code.
>>
>To indicate an empty loop body
>I find `{}` perfectly adequate
>on those odd occasions
>when it is needed.
>>
>Mind the gap.
>>
>[1] From my POV, natch.

>
Actually it makes perfect sense when you have your gate condition at the
top of the section - far easier to read, understand and maintain in many
cases (not all of course).
>
while(n--){
>
if(complexCondi tionNotMatched( n))
continue; /* not interested. Check the next if there is one. */
>
/*do processing of things we are interested in*/
>
}

This is exactly the kind of example that I find smelly. (Weakly
smelly, but still smelly.)

I would write the utterly obvious:

while (n--)
if (complexConditi onMatched(n))
doInterestingTh ings(n);

(Add layout and braces and inlined function body to taste.)

Now we could invert the test but then we need to scroll down to the end
of the function to be see what else happens after the block.

No, we don't. We just look; functions are not /that/ big, especially
nowadays, and editors are not that feeble, so I'm told.

Seems clear, maintainable and decent design to me. I fail to see how it
could be construed as "bad" in any shape or form.

It's not a clear statement of intent; or, more exactly, it's not as
clear a statement as one could write with similar effort.

--
'It changed the future .. and it changed us.' /Babylon 5/

Hewlett-Packard Limited registered no:
registered office: Cain Road, Bracknell, Berks RG12 1HN 690597 England

**Nick Keighley** · Sep 22 '08, 01:15 PM

Re: "Continue& quot; usage

On 22 Sep, 14:02, Ben Bacarisse <ben.use...@bsb .me.ukwrote:

Eric Sosman <esos...@ieee-dot-org.invalidwrit es:

mdh wrote:

May I ask the group this somewhat non-focused question....hav ing now
seen "continue" used in some of the solutions I have worked on.

<snip>

Hi, my name is Eric, and I'm a `continue' abuser. I use
it as a disguised `goto', simply to avoid excessive nesting:

>
<fx:stands up>
Hello, my name is Ben, and *I* abuse break. Ah, it feels so good to
say it out loud!
>
I never get tempted by continue (see elsethread) but I can't keep my
hands off that lovely break. It is sooooo tempting, when you are all
hot and bothered, tightly bound by a strict loop invariant, just to
slip in little break and be free.
>
[Serious point: in some ways, break is much worse than continue
because of what happens to the way you think about your loops, but I
find myself using break much more than continue and paying the extra
thinking costs later because I do try to verify the logic of all my
loops.]

I too am an inveterate break user and hardly ever use continue.
I think my continue is about the same as my goto usage.

As you say though break is potentially much worse. I think the
temptation to use it is because it it actually provides a useful
construct. continue seems to add confuscation without any particular
gain.

while (next_item() != end)
{
if (!match())
continue;

process_item();
}

seems less clear than

while (next_item() != end)
{
if (match())
process_item();
}

whilst I sometimes stuctures like this handy (and clear)

for (;;)
{
pre_process();
if (!more())
break;
post_process();
}

--
Nick Keighley

"Continue" usage

"Continue" usage

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