What would be the right warning/error?

[jacob navia]

Consider this code

static typedef struct {
int boo;
} FOO;

This provokes with MSVC:
------------------------------
Microsoft (R) C/C++ Optimizing Compiler Version 14.00.50727.762 for x64
Copyright (C) Microsoft Corporation. All rights reserved.

tstruct.c
tstruct.c(1) : error C2159: more than one storage class specified
------------------------------

With gcc we have:
----------------------------
root@ubuntu-vm:/tmp# gcc t.c
t.c:1: error: multiple storage classes in declaration specifiers
----------------------------

With lcc-win I had
Warning tstruct.c: 1 multiple types in a declaration. Last will be
used: 'typedef'

with lcc-win64
------------------------------
Warning tstruct.c: 1 multiple use of 'typedef'
------------------------------

All those warnings are misleading in my opinion. I have changed the
wording to:
Warning tstruct.c: 1 typedefs can't be static. Static keyword ignored

I think that this is much more clear but I have now some doubts:

Is this true?

My reasoning is that the static keyword can only apply to an
object, and a typedef is not an object. (Obviously there is
another obscure meaning to "static". Let's leave that for now)

Another problem is that both msvc and gcc say something about
"multiple storage classes" that I can't understand. Why that?

Note too that lcc-win issues just a warning. The other two issue
an error and compilation fails. Is this such a bad error that
warrants a failure to compiler the code?
--
jacob navia
jacob at jacob point remcomp point fr
logiciels/informatique
http://www.cs.virginia.edu/~lcc-win32

[Bartc]

"jacob navia" <ja***@nospam.comwrote in message
news:g2**********@aioe.org...

Consider this code

static typedef struct {
int boo;
} FOO;

This provokes with MSVC:
------------------------------
Microsoft (R) C/C++ Optimizing Compiler Version 14.00.50727.762 for x64
Copyright (C) Microsoft Corporation. All rights reserved.

tstruct.c
tstruct.c(1) : error C2159: more than one storage class specified

Another problem is that both msvc and gcc say something about
"multiple storage classes" that I can't understand. Why that?

I think that typedef is itself considered a storage class specifier (like
static), for purposes of syntax. And presumably you're only allowed one at a
time:

static int *a[10]; /* declares a variable a with static storage */
typedef int *b[10]; /* declares a type alias b */
--
Bartc

[crisgoogle]

On Jun 6, 8:09 am, jacob navia <[e-mail]:

Consider this code

static typedef struct {
int boo;

} FOO;

This provokes with MSVC:
------------------------------
Microsoft (R) C/C++ Optimizing Compiler Version 14.00.50727.762 for x64
Copyright (C) Microsoft Corporation. All rights reserved.

tstruct.c
tstruct.c(1) : error C2159: more than one storage class specified
------------------------------

With gcc we have:
----------------------------
root@ubuntu-vm:/tmp# gcc t.c
t.c:1: error: multiple storage classes in declaration specifiers
----------------------------

With lcc-win I had
Warning tstruct.c: 1 multiple types in a declaration. Last will be
used: 'typedef'

with lcc-win64
------------------------------
Warning tstruct.c: 1 multiple use of 'typedef'
------------------------------

All those warnings are misleading in my opinion. I have changed the
wording to:
Warning tstruct.c: 1 typedefs can't be static. Static keyword ignored

I think that this is much more clear but I have now some doubts:

Is this true?

Is what true? That the warnings are misleading? Well, "uninformative"
perhaps. That your warning is more explicit? Sure, okay. That typedefs
can't be static? Yes.

My reasoning is that the static keyword can only apply to an
object, and a typedef is not an object. (Obviously there is
another obscure meaning to "static". Let's leave that for now)

Another problem is that both msvc and gcc say something about
"multiple storage classes" that I can't understand. Why that?

I'm no compiler writer, but I'm guessing it's just the way the
compiler parses the code. "typedef" isn't a storage class (I don't
think <duck>), but it's certainly not a type either, which is what
would otherwise be required after that "static". I've seen many
compiler errors and warnings that are _far_ more obscure than this.

Note too that lcc-win issues just a warning. The other two issue
an error and compilation fails. Is this such a bad error that
warrants a failure to compiler the code?

Unless, as an extension, you document that construct to mean something
useful, I see no reason to allow the code to compile. It's almost
meaningless as it stands, won't compile on at least a couple of other
mainstream compilers, and is so simply fixed that a hard error seems
appropriate to me.

--

Cris

[crisgoogle]

On Jun 6, 8:44 am, [e-mail] wrote:

On Jun 6, 8:09 am, jacob navia <[e-mail]:

Consider this code

static typedef struct {
int boo;

} FOO;

This provokes with MSVC:
------------------------------
Microsoft (R) C/C++ Optimizing Compiler Version 14.00.50727.762 for x64
Copyright (C) Microsoft Corporation. All rights reserved.

tstruct.c
tstruct.c(1) : error C2159: more than one storage class specified
------------------------------

With gcc we have:
----------------------------
root@ubuntu-vm:/tmp# gcc t.c
t.c:1: error: multiple storage classes in declaration specifiers
----------------------------

With lcc-win I had
Warning tstruct.c: 1 multiple types in a declaration. Last will be
used: 'typedef'

with lcc-win64
------------------------------
Warning tstruct.c: 1 multiple use of 'typedef'
------------------------------

<snip>

Another problem is that both msvc and gcc say something about
"multiple storage classes" that I can't understand. Why that?

I'm no compiler writer, but I'm guessing it's just the way the
compiler parses the code. "typedef" isn't a storage class (I don't
think <duck>),

<snip>

Oops, and thirty seconds after posting, I look it up, and lo and
behold, "typedef" _is_ a storage class specifier ...

Sigh.

--

Cris

[Keith Thompson]

[My posts via rr.com still aren't showing up on aioe.org, so I'm
posting this through aioe.org so jacob can see it. I'm continuing
to post most of my articles through rr.com]

jacob navia <ja***@nospam.comwrites:

Consider this code

static typedef struct {
int boo;
} FOO;

This provokes with MSVC:
------------------------------
Microsoft (R) C/C++ Optimizing Compiler Version 14.00.50727.762 for x64
Copyright (C) Microsoft Corporation. All rights reserved.

tstruct.c
tstruct.c(1) : error C2159: more than one storage class specified
------------------------------

With gcc we have:
----------------------------
root@ubuntu-vm:/tmp# gcc t.c
t.c:1: error: multiple storage classes in declaration specifiers
----------------------------

Both of those seem reasonable.

With lcc-win I had
Warning tstruct.c: 1 multiple types in a declaration. Last will be
used: 'typedef'

with lcc-win64
------------------------------
Warning tstruct.c: 1 multiple use of 'typedef'
------------------------------

All those warnings are misleading in my opinion. I have changed the
wording to:
Warning tstruct.c: 1 typedefs can't be static. Static keyword ignored

I think that this is much more clear but I have now some doubts:

Is this true?

The warning is correct, as far as it goes, but the fact that your
diagnostic *doesn't* refer to multiple storage classes makes me
concerned that you might be missing some other cases.

My reasoning is that the static keyword can only apply to an
object, and a typedef is not an object. (Obviously there is
another obscure meaning to "static". Let's leave that for now)

Another problem is that both msvc and gcc say something about
"multiple storage classes" that I can't understand. Why that?

C99 6.7.1p3:

The typedef specifier is called a storage-class specifier for
syntactic convenience only; it is discussed in 6.7.7.

Note too that lcc-win issues just a warning. The other two issue
an error and compilation fails. Is this such a bad error that
warrants a failure to compiler the code?

Absolutely. Issuing a warning for code with a constraint violation
is, of course, permitted by the standard, but I can't imagine why
you'd want to do so in this case. I see no benefit from allowing the
user to leave this error uncorrected, or in blindly *guessing* that
the last storage class is what was intended.

You apparently treat this:
static typedef int foo;
as a typedef (ignoring "static"), and this:
typedef static int foo;
as a static object declaration. Both are simply errors.

(In another thread, you do something equally arbitrary for type
specifiers.)

--
Keith Thompson (The_Other_Keith) <ks***@mib.org>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Eric Sosman]

jacob navia wrote:

Consider this code

static typedef struct {
int boo;
} FOO;

This provokes with MSVC:
------------------------------
Microsoft (R) C/C++ Optimizing Compiler Version 14.00.50727.762 for x64
Copyright (C) Microsoft Corporation. All rights reserved.

tstruct.c
tstruct.c(1) : error C2159: more than one storage class specified
------------------------------

With gcc we have:
----------------------------
root@ubuntu-vm:/tmp# gcc t.c
t.c:1: error: multiple storage classes in declaration specifiers
----------------------------

With lcc-win I had
Warning tstruct.c: 1 multiple types in a declaration. Last will be
used: 'typedef'

with lcc-win64
------------------------------
Warning tstruct.c: 1 multiple use of 'typedef'
------------------------------

All those warnings are misleading in my opinion.

The first two seem to me more precise than the latter two,
but I'll grant that they might mislead someone who didn't know
that `typedef' was a storage class. The number of such someones
may be non-negligible, hence the potential to mislead may be
non-negligible.

I have changed the
wording to:
Warning tstruct.c: 1 typedefs can't be static. Static keyword ignored

I think that this is much more clear but I have now some doubts:

Is this true?

It is true that there can be at most one storage class
specifier in a declaration, so you can't have `static typedef'.
Nor can you have `typedef static' or `register typedef' or
`auto extern' or `static register' or ...

Another problem is that both msvc and gcc say something about
"multiple storage classes" that I can't understand. Why that?

Because `typedef' and `extern' and `static' and `auto' and
`register' are the storage-class specifiers (6.7.1). `typedef'
is an oddball (as noted in 6.7.1p3), but it's an s-c specifier
nonetheless.

Note too that lcc-win issues just a warning. The other two issue
an error and compilation fails. Is this such a bad error that
warrants a failure to compiler the code?

Purely a judgment call, with no clearly-defined Right Answer.
A diagnostic is required, but beyond that it's just your notion
of what would be most helpful to the user.

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

[jacob navia]

Eric Sosman wrote:

>All those warnings are misleading in my opinion.

The first two seem to me more precise than the latter two,
but I'll grant that they might mislead someone who didn't know
that `typedef' was a storage class. The number of such someones
may be non-negligible, hence the potential to mislead may be
non-negligible.

I didn't know that a typedef is a storage class. And now that
the appropiate parts of the standard have been cited I still
do not understand it.

#define FOO 8

the #define is not a storage class.

A typedef is a compile time alias for another type. Why should it
be a storage class?

Mystery.

--
jacob navia
jacob at jacob point remcomp point fr
logiciels/informatique
http://www.cs.virginia.edu/~lcc-win32

[jacob navia]

Keith Thompson wrote:

>
C99 6.7.1p3:

The typedef specifier is called a storage-class specifier for
syntactic convenience only; it is discussed in 6.7.7.

Note:

"FOR SYNTACTIC CONVENIENCE ONLY"

typedefs are surely not a storage class!

--
jacob navia
jacob at jacob point remcomp point fr
logiciels/informatique
http://www.cs.virginia.edu/~lcc-win32

[jacob navia]

jacob navia wrote:
[snip]

Thanks to all that replied.

--
jacob navia
jacob at jacob point remcomp point fr
logiciels/informatique
http://www.cs.virginia.edu/~lcc-win32

[Keith Thompson]

jacob navia <ja***@nospam.comwrites:

Eric Sosman wrote:

>>All those warnings are misleading in my opinion.

The first two seem to me more precise than the latter two,
but I'll grant that they might mislead someone who didn't know
that `typedef' was a storage class. The number of such someones
may be non-negligible, hence the potential to mislead may be
non-negligible.

I didn't know that a typedef is a storage class. And now that
the appropiate parts of the standard have been cited I still
do not understand it.

As the standard clearly says, it's "for syntactic convenience only".

I'm guessing that the inventor of "typedef" (presumably Dennis
Ritchie) decided what he wanted a declaration to look like, then
noticed that it fits exactly the same pattern as "static", "extern",
et al. These two declarations:

typedef int foo;
static int foo;

of course mean two very different things, but they follow exactly the
same pattern, the only *syntactic* difference being the different
keywords.

The point is to make the language a bit easier to describe, and to
make the job of compiler writers like you just a little bit simpler.

#define FOO 8

the #define is not a storage class.

Of course not. A macro definition is processed in a different
translation phase, and it has very different syntax *and* semantics
than either typedefs or (other) storage classes. There would be no
benefit in treating it as a storage class.

For a typedef, on the other hand, it's just *convenient* to use the
same syntax as for other storage classes.

Perhaps the standard would have been clearer if, rather than this:

storage-class-specifier:
typedef
extern
static
auto
register

it had defined this:

storage-class-specifier:
extern
static
auto
register

storage-class-specifier-or-typedef:
storage-class-specifier
typedef

and used "storage-class-specifier-or-typedef" wherever
"storage-class-specifier" is used now. I'd probably advocate doing it
that way if the existing definition weren't already well established,
but once you understand what's going on, I don't find the existing
definition to be all that troubling. But you could always use my
proposed modification within your own compiler. Unless I've made a
mistake, it will accept exactly the same set of syntactically valid
translation units, and might make it a bit easier to generate clear
diagnostics. But you can already do that by treating "typedef" as a
special case of the set of storage classes.

A typedef is a compile time alias for another type. Why should it
be a storage class?

See above.

Mystery.

Not really.

--
Keith Thompson (The_Other_Keith) <ks***@mib.org>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Keith Thompson]

jacob navia <ja***@nospam.comwrites:

Keith Thompson wrote:

>>
C99 6.7.1p3:

The typedef specifier is called a storage-class specifier for
syntactic convenience only; it is discussed in 6.7.7.

Note:

"FOR SYNTACTIC CONVENIENCE ONLY"

YES, IT'S FOR SYNTACTIC CONVENIENCE ONLY. WHY ARE WE SHOUTING?

typedefs are surely not a storage class!

The standard says they are. If you don't want to follow the
standard's terminology, nobody is forcing you to do so. But I note
that your failure to do so in this case has caused you to introduce a
bug into your compiler. (By "bug" I don't necessarily mean a failure
to conform to the standard's requirements.)

--
Keith Thompson (The_Other_Keith) <ks***@mib.org>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[CBFalconer]

jacob navia wrote:

>

.... snip ...

>
#define FOO 8

the #define is not a storage class.

A typedef is a compile time alias for another type. Why should it
be a storage class?

#define p1 int*
typedef p2 int*;

p1 a1, b1;
p2 a2, b2;

note that a1, a2, and b2 are pointers. b1 is an int object.

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

** Posted from http://www.teranews.com **

[Eric Sosman]

jacob navia wrote:

>
I didn't know that a typedef is a storage class. And now that
the appropiate parts of the standard have been cited I still
do not understand it.

#define FOO 8

the #define is not a storage class.

A typedef is a compile time alias for another type. Why should it
be a storage class?

There are multiple possible answers ...

One answer might be "It's a storage class specifier because
the Standard says so," but that might not satisfy the curious
mind. It's like answering "Why is murder a crime?" with
"Because there's a law against it." Still, on one level it's
the truth, just like "Why does ^ mean exclusive-or instead of
exponentiation?" or "Why is it `struct' and not `record'?"

Probing a little deeper, we see that the Standard itself
says (in normative text, no less) that `typedef' is a storage
class specifier as a matter of convenience. So, what is made
more convenient by this peculiar choice? Well, as you said at
the beginning, `typedef' conflicts with `static' -- and with
`extern' and `auto' and `register', too, and all those four
conflict with each other. So lumping `typedef' in with the
others allows the "one storage class" rule of 6.7.1p2 to be
expressed succinctly. If `typedef' were handled separately,
the rule would have to be something like

At most, one storage-class specifier may be given in
the declaration specifiers in a declaration, except
that if the declaration specifiers include `typedef'
then no storage-class specifier may be given.

And then there's the grammar. `typedef' can appear at all
the same places the "real" storage classes can, and groups with
the other bits of a declaration the same way they do, so it's
convenient to lump them under the same nonterminal. If `typedef'
were handled separately, you'd also need something like

typedef-or-storage-class-specifier:
typedef
storage-class-specifier

storage-class-specifier:
extern
static
auto
register

.... and you'd scratch your head trying to figure out what value
the extra nonterminal brings to the party.

The Rationale doesn't mention the matter, but probing all
the way back to K&R Classic we find "Syntactically, typedef is
like the storage classes extern, static, etc." (p. 140), and
we find `typedef' listed among the storage class specifiers
(p. 192), with the same "syntactic convenience" remark that
the Standard uses. So the treatment of `typedef' as a storage
class specifier is not a new aberration; it is at worst a time-
honored aberration. Or "hallowed tradition," as we say in
America when we're running for political office.

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

[Serve Lau]

"jacob navia" <ja***@nospam.comschreef in bericht
news:g2**********@aioe.org...

Consider this code

static typedef struct {
int boo;
} FOO;

This provokes with MSVC:
------------------------------
Microsoft (R) C/C++ Optimizing Compiler Version 14.00.50727.762 for x64
Copyright (C) Microsoft Corporation. All rights reserved.

tstruct.c
tstruct.c(1) : error C2159: more than one storage class specified
------------------------------

With gcc we have:
----------------------------
root@ubuntu-vm:/tmp# gcc t.c
t.c:1: error: multiple storage classes in declaration specifiers
----------------------------

With lcc-win I had
Warning tstruct.c: 1 multiple types in a declaration. Last will be
used: 'typedef'

with lcc-win64
------------------------------
Warning tstruct.c: 1 multiple use of 'typedef'
------------------------------

All those warnings are misleading in my opinion. I have changed the
wording to:
Warning tstruct.c: 1 typedefs can't be static. Static keyword ignored

what if you say
register typedef struct...
or
extern typedef struct...

etc.

I noticed that MSVC compiles the following with no complaints.

const typedef struct {
int boo;
} FOO;

Is that correct?

[Richard Tobin]

In article <1212768389.979717@news1nwk>,
Eric Sosman <Er*********@sun.comwrote:

It is true that there can be at most one storage class
specifier in a declaration, so you can't have `static typedef'.

I think Jacob is right to try to give a more specific error message in
this case. "typedef" may be a storage class as far as the standard is
concerned, but that's just the standard-writer's trick for terseness,
and an error message has other goals.

-- Richard
--
In the selection of the two characters immediately succeeding the numeral 9,
consideration shall be given to their replacement by the graphics 10 and 11 to
facilitate the adoption of the code in the sterling monetary area. (X3.4-1963)

[Richard Heathfield]

CBFalconer said:

jacob navia wrote:

>>

... snip ...

>>
#define FOO 8

the #define is not a storage class.

A typedef is a compile time alias for another type. Why should it
be a storage class?

#define p1 int*
typedef p2 int*;

p1 a1, b1;
p2 a2, b2;

note that a1, a2, and b2 are pointers. b1 is an int object.

Note that typedef p2 int*; is a syntax error, and neither a2 nor b2 have
any meaning whatsoever.

--
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

[Richard]

CBFalconer <cb********@yahoo.comwrites:

jacob navia wrote:

>>

... snip ...

>>
#define FOO 8

the #define is not a storage class.

A typedef is a compile time alias for another type. Why should it
be a storage class?

#define p1 int*
typedef p2 int*;

p1 a1, b1;
p2 a2, b2;

note that a1, a2, and b2 are pointers. b1 is an int object.

No they are not. p2 is nothing since it can not compile.

I assume you mean something more like:

typedef int * p2;

[Keith Thompson]

ri*****@cogsci.ed.ac.uk (Richard Tobin) writes:

In article <1212768389.979717@news1nwk>,
Eric Sosman <Er*********@sun.comwrote:

> It is true that there can be at most one storage class
specifier in a declaration, so you can't have `static typedef'.

I think Jacob is right to try to give a more specific error message in
this case. "typedef" may be a storage class as far as the standard is
concerned, but that's just the standard-writer's trick for terseness,
and an error message has other goals.

Agreed.

One cannot reasonably dispute that "typedef" is a
"storage-class-specifier" *according to the standard* (since it's the
standard that defines the term "storage-class-specifier"). But
there's no requirement, and in this particular case perhaps no good
reason, to use the standard's terminology in a diagnostic. The
purpose of a diagnostic is to explain something to the user, with the
goal of letting the user figure out how to correct the error.
(Personally, I like seeing error messages that cite chapter and verse
in the standard, but I'm not a typical user.)

I don't know what kind of parser lcc-win (or it's predecessor lcc)
uses internally. Presumably there's a description of the C grammar,
either explicitly or implicitly. It's likely that this grammar
follows the standard's grammar in treating "typedef" as a
storage-class-specifier. But a little extra work to treat it as a
special case when printing an error message would be worthwhile.

Or, for that matter, the message could be something like "foo and bar
may not be used in the same declaration", where foo and bar are
replaced with whatever storage-class-specifiers appear in the
incorrect code. In this case, there isn't even a need to mention
storage-class specifiers. (Generating a reasonable diagnostic for
three or more is left as an exercise.)

--
Keith Thompson (The_Other_Keith) <ks***@mib.org>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[CBFalconer]

Richard Heathfield wrote:

CBFalconer said:

>jacob navia wrote:

>>>

... snip ...

>>>
#define FOO 8

the #define is not a storage class.

A typedef is a compile time alias for another type. Why should
it be a storage class?

#define p1 int*
typedef p2 int*;

p1 a1, b1;
p2 a2, b2;

note that a1, a2, and b2 are pointers. b1 is an int object.

Note that typedef p2 int*; is a syntax error, and neither a2 nor
b2 have any meaning whatsoever.

Will you settle for:

typedef int* p2;

Wouldn't it be slightly easier on all to simply post a correction?

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

[Richard Heathfield]

CBFalconer said:

Richard Heathfield wrote:

<snip>

>>
Note that typedef p2 int*; is a syntax error, and neither a2 nor
b2 have any meaning whatsoever.

Will you settle for:

typedef int* p2;

No, but at least now it's syntactically correct, which is a start, I
suppose.

>
Wouldn't it be slightly easier on all to simply post a correction?

I didn't realise you needed one.

--
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

[Richard Bos]

jacob navia <ja***@nospam.comwrote:

Eric Sosman wrote:

All those warnings are misleading in my opinion.

The first two seem to me more precise than the latter two,
but I'll grant that they might mislead someone who didn't know
that `typedef' was a storage class. The number of such someones
may be non-negligible, hence the potential to mislead may be
non-negligible.

I didn't know that a typedef is a storage class.

In a compiler implementor, that's scary.

Richard