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No Spam
Guest
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 Posted: Sun Dec 14, 2003 2:00 am Post subject: Variables in for loop - language change? |
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Is this way of declaring variables no longer allowed by the standard?
for (int i=0;i
{
...
}
Gnu compiler complains about this; Microsoft doesn't.
Under Gnu, must change to
int i;
for (i=0;i
{
...
}
The first way of declaring i inside the for statement is mention in
the 3rd edition of "The C++ Programming Language" [Strousptrup]
and "The Annotated C++ Reference Manual" [Ellis and Stroupstrup].
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Jack Klein
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| Posted: Sun Dec 14, 2003 11:06 am Post subject: Re: Variables in for loop - language change? |
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On 13 Dec 2003 21:00:14 -0500, "No Spam" <nospam (AT) myisp (DOT) net> wrote in
comp.lang.c++.moderated:
| Quote: | Is this way of declaring variables no longer allowed by the standard?
for (int i=0;i
{
...
}
Gnu compiler complains about this; Microsoft doesn't.
|
What GNU compiler? There have been many versions. Older ones did not
support this, as it was not part of C++. Newer ones do support it, as
it became part of standard C++.
And are you invoking whatever version of the compiler as a C or a C++
compiler?
--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
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James Dennett
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| Posted: Sun Dec 14, 2003 11:07 am Post subject: Re: Variables in for loop - language change? |
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No Spam wrote:
| Quote: | Is this way of declaring variables no longer allowed by the standard?
for (int i=0;i
{
...
}
Gnu compiler complains about this; Microsoft doesn't.
|
No GNU C++ compiler I can remember using has ever
complained about this in C++ code. GCC even gets
the rules right about where the scope of i ends,
and Microsoft have only just changed to getting
that right. (In their defense, compiler vendors
are sometimes trapped between standards compliance
and not breaking their customers' code.)
| Quote: | Under Gnu, must change to
int i;
for (i=0;i
{
...
}
The first way of declaring i inside the for statement is mention in
the 3rd edition of "The C++ Programming Language" [Strousptrup]
and "The Annotated C++ Reference Manual" [Ellis and Stroupstrup].
|
Both C and C++ allow the first form now, though C adopted
it only in 1999.
If you do need further information on this, you might try
a few things:
(1) Give the exact error text and a short, close-to-compilable
example which reproduces the error
(2) Say which versions of compilers you are talking about.
The second is important here because GCC's C++ support only
became anywhere near supporting standard C++ with 2.95, and
only a good approximation to a compliant compiler with 3.0
or later.
Is it possible that your code is assuming that the following
is correct?
int main() {
for (int i = 0; i != 10; ++i) {
// empty loop for exposition
}
i = 0;
}
Visual C++ 6 would compile that, though it is not valid C++;
there is no variable called "i" in scope for the "i = 0;"
statement.
-- James.
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Francis Glassborow
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| Posted: Sun Dec 14, 2003 3:34 pm Post subject: Re: Variables in for loop - language change? |
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In article <pqJCb.71009$_J.62395 (AT) newssvr25 (DOT) news.prodigy.com>, No Spam
<nospam (AT) myisp (DOT) net> writes
| Quote: | Is this way of declaring variables no longer allowed by the standard?
for (int i=0;i
{
...
}
Gnu compiler complains about this; Microsoft doesn't.
Under Gnu, must change to
int i;
for (i=0;i
{
...
}
Looks to me as if you are using Gnu compiler in C89/90 mode. |
--
Francis Glassborow ACCU
Author of 'You Can Do It!' see http://www.spellen.org/youcandoit
or http://www.robinton.demon.co.uk
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Chris Mantoulidis
Guest
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| Posted: Sun Dec 14, 2003 4:54 pm Post subject: Re: Variables in for loop - language change? |
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| Quote: | Is this way of declaring variables no longer allowed by the standard?
for (int i=0;i
{
...
}
|
Of course it's allowed!!!
| Quote: | Gnu compiler complains about this; Microsoft doesn't.
|
Well, then you've got an error. Not the compiler's fault...
| Quote: | Under Gnu, must change to
int i;
for (i=0;i
{
...
}
|
Nono!!!
You gotta use the second way if you want to use "i" in 2 or more for
loops... If you use if for just one loop, the 1st way works.
Example...
.....
int main()
{
//you CAN do that
for (int i = 0; i < 10; i++)
cout << "foo no. " << i << endl;
return 0;
}
2nd example:
.....
int main()
{
int i;
//here you canNOT do the above because you will use "i" in some
other
//loop
for (i = 0; i < 20; i++)
cout << "foo no. " << i <
for (i = 4; i < 40; i++)
cout << "bar no. " << i << endl;
return 0;
}
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Xenos
Guest
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| Posted: Mon Dec 15, 2003 10:05 pm Post subject: Re: Variables in for loop - language change? |
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"Chris Mantoulidis" <cmad_x (AT) yahoo (DOT) com> wrote
| Quote: | Is this way of declaring variables no longer allowed by the standard?
for (int i=0;i
{
...
}
Of course it's allowed!!!
Gnu compiler complains about this; Microsoft doesn't.
Well, then you've got an error. Not the compiler's fault...
Under Gnu, must change to
int i;
for (i=0;i
{
...
}
Nono!!!
You gotta use the second way if you want to use "i" in 2 or more for
loops... If you use if for just one loop, the 1st way works.
Example...
....
int main()
{
//you CAN do that
for (int i = 0; i < 10; i++)
cout << "foo no. " << i << endl;
return 0;
}
2nd example:
....
int main()
{
int i;
//here you canNOT do the above because you will use "i" in some
other
//loop
for (i = 0; i < 20; i++)
cout << "foo no. " << i <
for (i = 4; i < 40; i++)
cout << "bar no. " << i << endl;
return 0;
}
|
Why do you think you need the second why to use i in multiple loops? You
only need to declare it outside the loop if you want to access it outside
the loop.
DrX
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Kevin Saff
Guest
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| Posted: Tue Dec 16, 2003 8:50 pm Post subject: Re: Variables in for loop - language change? |
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"Chris Mantoulidis" <cmad_x (AT) yahoo (DOT) com> wrote
| Quote: |
You gotta use the second way if you want to use "i" in 2 or more for
loops... If you use if for just one loop, the 1st way works.
Example...
[SNIP]
....
int main()
{
int i;
file://here you canNOT do the above because you will use "i" in some
other
file://loop
for (i = 0; i < 20; i++)
cout << "foo no. " << i <
for (i = 4; i < 40; i++)
cout << "bar no. " << i << endl;
return 0;
}
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No, you only have to do this in MSVC6. Maybe if you got a C++ compiler, you
wouldn't have these problems. :)
--
KCS
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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Xenos
Guest
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| Posted: Thu Dec 18, 2003 8:47 am Post subject: Re: Variables in for loop - language change? |
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"Kevin Saff" <google.com (AT) kevin (DOT) saff.net> wrote
| Quote: | "Chris Mantoulidis" <cmad_x (AT) yahoo (DOT) com> wrote in message
news:a8587dd9.0312140616.678f76bc (AT) posting (DOT) google.com...
No, you only have to do this in MSVC6. Maybe if you got a C++ compiler,
you
wouldn't have these problems. :)
--
KCS
A simple, but kludgy, fix for the MSVC6 scoping problem with for loops is |
this:
#define for if (0); else for
DrX
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kanze@gabi-soft.fr
Guest
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| Posted: Fri Dec 19, 2003 11:16 am Post subject: Re: Variables in for loop - language change? |
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Xenos <dont.spam.me (AT) spamhate (DOT) com> wrote
| Quote: | "Kevin Saff" <google.com (AT) kevin (DOT) saff.net> wrote in message
news:Hpzyrt.C1z (AT) news (DOT) boeing.com...
"Chris Mantoulidis" <cmad_x (AT) yahoo (DOT) com> wrote in message
news:a8587dd9.0312140616.678f76bc (AT) posting (DOT) google.com...
No, you only have to do this in MSVC6. Maybe if you got a C++
compiler, you wouldn't have these problems. :)
A simple, but kludgy, fix for the MSVC6 scoping problem with for loops
is this:
#define for if (0); else for
|
A much better solution is to just write clean code which is legal with
both C++ scoping rules. Most of the time, cleaning written,
understandable code will compiler equally well under both rules.
--
James Kanze GABI Software mailto:kanze (AT) gabi-soft (DOT) fr
Conseils en informatique orientée objet/ http://www.gabi-soft.fr
Beratung in objektorientierter Datenverarbeitung
11 rue de Rambouillet, 78460 Chevreuse, France, +33 (0)1 30 23 45 16
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