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Is it legal to define an unnamed struct?
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Is the following code legal?:
struct
int x;
;
This code simply defines an unnamed structure. I do not intend to create objects of this type, nor do I need this structure in any other way. It simply appears in the source as a side effect of some complex macro expansion.
Useless though it is, I see no problem with it. Just another piece of code that can be compiled and then optimized out completely.
However, in the real world the outcome is quite different from my expectations:
GCC 8.3 reports an error:
error: abstract declarator '<unnamed struct>' used as declaration
Clang 8.0.0 reports an error too:
error: anonymous structs and classes must be class members
warning: declaration does not declare anything [-Wmissing-declarations]
Only MSVC 2017 sees no problem with such source.
So, the question is: who's right? Is there a relevant quote from the Standard that explicitly forbids such declarations?
Edit:
The project uses C++11. But the error messages are the same for C++98, C++11 and C++17.
c++ c++11 unnamed-class
edited Apr 30 at 16:48
Boann
37.8k1291123
asked Apr 30 at 7:49
Igor GIgor G
1859
add a comment |
Is the following code legal?:
struct
int x;
;
This code simply defines an unnamed structure. I do not intend to create objects of this type, nor do I need this structure in any other way. It simply appears in the source as a side effect of some complex macro expansion.
Useless though it is, I see no problem with it. Just another piece of code that can be compiled and then optimized out completely.
However, in the real world the outcome is quite different from my expectations:
GCC 8.3 reports an error:
error: abstract declarator '<unnamed struct>' used as declaration
Clang 8.0.0 reports an error too:
error: anonymous structs and classes must be class members
warning: declaration does not declare anything [-Wmissing-declarations]
Only MSVC 2017 sees no problem with such source.
So, the question is: who's right? Is there a relevant quote from the Standard that explicitly forbids such declarations?
Edit:
The project uses C++11. But the error messages are the same for C++98, C++11 and C++17.
c++ c++11 unnamed-class
edited Apr 30 at 16:48
Boann
37.8k1291123
asked Apr 30 at 7:49
Igor GIgor G
1859
According to stackoverflow.com/a/12785369/969365 C++ does not allow anonymous structs (but it says that C11 does, and that future revisions to C++ might add support). Note that there are differences between anonoymous structs and unnamed structs.
– simon
Apr 30 at 7:54
cplusplus.com/forum/general/138733
– Mayur
Apr 30 at 7:55
stackoverflow.com/questions/2253878/…
– Ville-Valtteri
Apr 30 at 8:03
Microsoft's compiler has (and the Windows headers use) an utterly pointless thing called an anonymous struct. That's why it accepts that code.
– Pete Becker
Apr 30 at 12:33
add a comment |
Is the following code legal?:
struct
int x;
;
This code simply defines an unnamed structure. I do not intend to create objects of this type, nor do I need this structure in any other way. It simply appears in the source as a side effect of some complex macro expansion.
Useless though it is, I see no problem with it. Just another piece of code that can be compiled and then optimized out completely.
However, in the real world the outcome is quite different from my expectations:
GCC 8.3 reports an error:
error: abstract declarator '<unnamed struct>' used as declaration
Clang 8.0.0 reports an error too:
error: anonymous structs and classes must be class members
warning: declaration does not declare anything [-Wmissing-declarations]
Only MSVC 2017 sees no problem with such source.
So, the question is: who's right? Is there a relevant quote from the Standard that explicitly forbids such declarations?
Edit:
The project uses C++11. But the error messages are the same for C++98, C++11 and C++17.
c++ c++11 unnamed-class
edited Apr 30 at 16:48
Boann
37.8k1291123
asked Apr 30 at 7:49
Igor GIgor G
1859
Is the following code legal?:
struct
int x;
;
This code simply defines an unnamed structure. I do not intend to create objects of this type, nor do I need this structure in any other way. It simply appears in the source as a side effect of some complex macro expansion.
Useless though it is, I see no problem with it. Just another piece of code that can be compiled and then optimized out completely.
However, in the real world the outcome is quite different from my expectations:
GCC 8.3 reports an error:
error: abstract declarator '<unnamed struct>' used as declaration
Clang 8.0.0 reports an error too:
error: anonymous structs and classes must be class members
warning: declaration does not declare anything [-Wmissing-declarations]
Only MSVC 2017 sees no problem with such source.
So, the question is: who's right? Is there a relevant quote from the Standard that explicitly forbids such declarations?
Edit:
The project uses C++11. But the error messages are the same for C++98, C++11 and C++17.
c++ c++11 unnamed-class
c++ c++11 unnamed-class
edited Apr 30 at 16:48
Boann
37.8k1291123
asked Apr 30 at 7:49
Igor GIgor G
1859
edited Apr 30 at 16:48
Boann
37.8k1291123
asked Apr 30 at 7:49
Igor GIgor G
1859
edited Apr 30 at 16:48
Boann
37.8k1291123
edited Apr 30 at 16:48
Boann
37.8k1291123
edited Apr 30 at 16:48
Boann
37.8k1291123
37.8k1291123
asked Apr 30 at 7:49
Igor GIgor G
1859
asked Apr 30 at 7:49
Igor GIgor G
1859
asked Apr 30 at 7:49
Igor GIgor G
1859
1859
According to stackoverflow.com/a/12785369/969365 C++ does not allow anonymous structs (but it says that C11 does, and that future revisions to C++ might add support). Note that there are differences between anonoymous structs and unnamed structs.
– simon
Apr 30 at 7:54
cplusplus.com/forum/general/138733
– Mayur
Apr 30 at 7:55
stackoverflow.com/questions/2253878/…
– Ville-Valtteri
Apr 30 at 8:03
Microsoft's compiler has (and the Windows headers use) an utterly pointless thing called an anonymous struct. That's why it accepts that code.
– Pete Becker
Apr 30 at 12:33
add a comment |
According to stackoverflow.com/a/12785369/969365 C++ does not allow anonymous structs (but it says that C11 does, and that future revisions to C++ might add support). Note that there are differences between anonoymous structs and unnamed structs.
– simon
Apr 30 at 7:54
cplusplus.com/forum/general/138733
– Mayur
Apr 30 at 7:55
stackoverflow.com/questions/2253878/…
– Ville-Valtteri
Apr 30 at 8:03
Microsoft's compiler has (and the Windows headers use) an utterly pointless thing called an anonymous struct. That's why it accepts that code.
– Pete Becker
Apr 30 at 12:33
According to stackoverflow.com/a/12785369/969365 C++ does not allow anonymous structs (but it says that C11 does, and that future revisions to C++ might add support). Note that there are differences between anonoymous structs and unnamed structs.
– simon
Apr 30 at 7:54
According to stackoverflow.com/a/12785369/969365 C++ does not allow anonymous structs (but it says that C11 does, and that future revisions to C++ might add support). Note that there are differences between anonoymous structs and unnamed structs.
– simon
Apr 30 at 7:54
cplusplus.com/forum/general/138733
– Mayur
Apr 30 at 7:55
cplusplus.com/forum/general/138733
– Mayur
Apr 30 at 7:55
stackoverflow.com/questions/2253878/…
– Ville-Valtteri
Apr 30 at 8:03
stackoverflow.com/questions/2253878/…
– Ville-Valtteri
Apr 30 at 8:03
Microsoft's compiler has (and the Windows headers use) an utterly pointless thing called an anonymous struct. That's why it accepts that code.
– Pete Becker
Apr 30 at 12:33
Microsoft's compiler has (and the Windows headers use) an utterly pointless thing called an anonymous struct. That's why it accepts that code.
– Pete Becker
Apr 30 at 12:33
add a comment |
1 Answer
1
active
oldest
votes
No, it is not allowed. GCC and Clang are right.
Per [dcl.dcl]/3 (7 Declarations) in N3337 (C++11 final draft), a class declaration must introduce at one name to the program. For example, the following are invalid:
enum ;
typedef class ;
(Note: this isn't unique to C++11. In N4140 (C++14 final draft) it is [dcl.dcl]/5 (7 Declarations). In N4659 (C++17 final draft) it is [dcl.dcl]/5 (10 Declarations).)
answered Apr 30 at 8:01
L. F.L. F.
2,125629
The question is tagged c++11, and the wording isn't there for N3337
– StoryTeller
Apr 30 at 8:05
2
@StoryTeller In N3337, it is [dcl.dcl]/3
– Ville-Valtteri
Apr 30 at 8:07
1
Doesn'tstruct int n; ;introduce the name::<anonymous struct>::n?
– YSC
Apr 30 at 8:10
4
@YSC - That's not a name.
– StoryTeller
Apr 30 at 8:14
3
@YSC - Yes, and in the scope of a class, a name may refer to a member. The fact you need to fully qualify it, means it doesn't introduce that name at all. This is about declarative regions and scopes.
– StoryTeller
Apr 30 at 8:19
|
show 6 more comments
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1 Answer
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1 Answer
1
active
oldest
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oldest
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active
oldest
votes
No, it is not allowed. GCC and Clang are right.
Per [dcl.dcl]/3 (7 Declarations) in N3337 (C++11 final draft), a class declaration must introduce at one name to the program. For example, the following are invalid:
enum ;
typedef class ;
(Note: this isn't unique to C++11. In N4140 (C++14 final draft) it is [dcl.dcl]/5 (7 Declarations). In N4659 (C++17 final draft) it is [dcl.dcl]/5 (10 Declarations).)
answered Apr 30 at 8:01
L. F.L. F.
2,125629
The question is tagged c++11, and the wording isn't there for N3337
– StoryTeller
Apr 30 at 8:05
2
@StoryTeller In N3337, it is [dcl.dcl]/3
– Ville-Valtteri
Apr 30 at 8:07
1
Doesn'tstruct int n; ;introduce the name::<anonymous struct>::n?
– YSC
Apr 30 at 8:10
4
@YSC - That's not a name.
– StoryTeller
Apr 30 at 8:14
3
@YSC - Yes, and in the scope of a class, a name may refer to a member. The fact you need to fully qualify it, means it doesn't introduce that name at all. This is about declarative regions and scopes.
– StoryTeller
Apr 30 at 8:19
|
show 6 more comments
No, it is not allowed. GCC and Clang are right.
Per [dcl.dcl]/3 (7 Declarations) in N3337 (C++11 final draft), a class declaration must introduce at one name to the program. For example, the following are invalid:
enum ;
typedef class ;
(Note: this isn't unique to C++11. In N4140 (C++14 final draft) it is [dcl.dcl]/5 (7 Declarations). In N4659 (C++17 final draft) it is [dcl.dcl]/5 (10 Declarations).)
answered Apr 30 at 8:01
L. F.L. F.
2,125629
The question is tagged c++11, and the wording isn't there for N3337
– StoryTeller
Apr 30 at 8:05
2
@StoryTeller In N3337, it is [dcl.dcl]/3
– Ville-Valtteri
Apr 30 at 8:07
1
Doesn'tstruct int n; ;introduce the name::<anonymous struct>::n?
– YSC
Apr 30 at 8:10
4
@YSC - That's not a name.
– StoryTeller
Apr 30 at 8:14
3
@YSC - Yes, and in the scope of a class, a name may refer to a member. The fact you need to fully qualify it, means it doesn't introduce that name at all. This is about declarative regions and scopes.
– StoryTeller
Apr 30 at 8:19
|
show 6 more comments
No, it is not allowed. GCC and Clang are right.
Per [dcl.dcl]/3 (7 Declarations) in N3337 (C++11 final draft), a class declaration must introduce at one name to the program. For example, the following are invalid:
enum ;
typedef class ;
(Note: this isn't unique to C++11. In N4140 (C++14 final draft) it is [dcl.dcl]/5 (7 Declarations). In N4659 (C++17 final draft) it is [dcl.dcl]/5 (10 Declarations).)
answered Apr 30 at 8:01
L. F.L. F.
2,125629
No, it is not allowed. GCC and Clang are right.
Per [dcl.dcl]/3 (7 Declarations) in N3337 (C++11 final draft), a class declaration must introduce at one name to the program. For example, the following are invalid:
enum ;
typedef class ;
(Note: this isn't unique to C++11. In N4140 (C++14 final draft) it is [dcl.dcl]/5 (7 Declarations). In N4659 (C++17 final draft) it is [dcl.dcl]/5 (10 Declarations).)
answered Apr 30 at 8:01
L. F.L. F.
2,125629
edited May 1 at 2:02
answered Apr 30 at 8:01
L. F.L. F.
2,125629
answered Apr 30 at 8:01
L. F.L. F.
2,125629
answered Apr 30 at 8:01
L. F.L. F.
2,125629
2,125629
The question is tagged c++11, and the wording isn't there for N3337
– StoryTeller
Apr 30 at 8:05
2
@StoryTeller In N3337, it is [dcl.dcl]/3
– Ville-Valtteri
Apr 30 at 8:07
1
Doesn'tstruct int n; ;introduce the name::<anonymous struct>::n?
– YSC
Apr 30 at 8:10
4
@YSC - That's not a name.
– StoryTeller
Apr 30 at 8:14
3
@YSC - Yes, and in the scope of a class, a name may refer to a member. The fact you need to fully qualify it, means it doesn't introduce that name at all. This is about declarative regions and scopes.
– StoryTeller
Apr 30 at 8:19
|
show 6 more comments
The question is tagged c++11, and the wording isn't there for N3337
– StoryTeller
Apr 30 at 8:05
2
@StoryTeller In N3337, it is [dcl.dcl]/3
– Ville-Valtteri
Apr 30 at 8:07
1
Doesn'tstruct int n; ;introduce the name::<anonymous struct>::n?
– YSC
Apr 30 at 8:10
4
@YSC - That's not a name.
– StoryTeller
Apr 30 at 8:14
3
@YSC - Yes, and in the scope of a class, a name may refer to a member. The fact you need to fully qualify it, means it doesn't introduce that name at all. This is about declarative regions and scopes.
– StoryTeller
Apr 30 at 8:19
The question is tagged c++11, and the wording isn't there for N3337
– StoryTeller
Apr 30 at 8:05
The question is tagged c++11, and the wording isn't there for N3337
– StoryTeller
Apr 30 at 8:05
2
2
@StoryTeller In N3337, it is [dcl.dcl]/3
– Ville-Valtteri
Apr 30 at 8:07
@StoryTeller In N3337, it is [dcl.dcl]/3
– Ville-Valtteri
Apr 30 at 8:07
1
1
Doesn't
struct int n; ; introduce the name ::<anonymous struct>::n?– YSC
Apr 30 at 8:10
Doesn't
struct int n; ; introduce the name ::<anonymous struct>::n?– YSC
Apr 30 at 8:10
4
4
@YSC - That's not a name.
– StoryTeller
Apr 30 at 8:14
@YSC - That's not a name.
– StoryTeller
Apr 30 at 8:14
3
3
@YSC - Yes, and in the scope of a class, a name may refer to a member. The fact you need to fully qualify it, means it doesn't introduce that name at all. This is about declarative regions and scopes.
– StoryTeller
Apr 30 at 8:19
@YSC - Yes, and in the scope of a class, a name may refer to a member. The fact you need to fully qualify it, means it doesn't introduce that name at all. This is about declarative regions and scopes.
– StoryTeller
Apr 30 at 8:19
|
show 6 more comments
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According to stackoverflow.com/a/12785369/969365 C++ does not allow anonymous structs (but it says that C11 does, and that future revisions to C++ might add support). Note that there are differences between anonoymous structs and unnamed structs.
– simon
Apr 30 at 7:54
cplusplus.com/forum/general/138733
– Mayur
Apr 30 at 7:55
stackoverflow.com/questions/2253878/…
– Ville-Valtteri
Apr 30 at 8:03
Microsoft's compiler has (and the Windows headers use) an utterly pointless thing called an anonymous struct. That's why it accepts that code.
– Pete Becker
Apr 30 at 12:33