Struct declaration with no tag and no init-declarator-list

[JoseMariaSola]

The following declaration is valid:

struct {int x;};

There's no tag and no variable.

Does it has any use?

Thanks.

Joey.

 

[viza]

Hi

struct {int x;};

There's no tag and no variable.

Does it has any use?

On it's own, it does nothing. Inside another struct or union, its
member(s) can be accessed as if they were members of the parent. eg:

struct {
struct {int x;};
}
foo;

foo. x= 7;

which is easier than:

struct {
struct {int x;} bar;
}
foo;

foo. bar. x= 7;

HTH

viza

 

[viza]

On it's own, it does nothing. Inside another struct or union, its
member(s) can be accessed as if they were members of the parent. eg:

PS: I didn't realise that that's non-standard. Flames may follow...

 

[Harald van Dijk]

The following declaration is valid:

struct {int x;};

No, it isn't. It's not a syntax error, but C requires a declaration to
actually declare something.

 

[Keith Thompson]

On it's own, it does nothing. Inside another struct or union, its
member(s) can be accessed as if they were members of the parent. eg:

struct {
struct {int x;};
}
foo;

foo. x= 7;

which is easier than:

struct {
struct {int x;} bar;
}
foo;

foo. bar. x= 7;

No, you can't, at least not in standard C. Some compilers may offer
it as an extension. But if you want your code to be portable, you'll
just have to write "foo.bar.x" (or do some ugly macro stuff).

 

[JoseMariaSola]

The following declaration is valid:

No, it isn't. It's not a syntax error, but C requires a declaration to
actually declare something.

Is it a static semantic error? My compiler doesn't detect it. Is it
broken?
In the Standard I didn't find any restriction.

 

[Harald van Dijk]

Is it a static semantic error?

It's a constraint violation, which requires a diagnostic from any
conforming implementation.

My compiler doesn't detect it. Is it
broken?

If you asked it to try to conform to the standard, then yes.

In the Standard I didn't find any restriction.

It's in 6.7p2: "A declaration shall declare at least a declarator (other
than the parameters of a function or the members of a structure or union),
a tag, or the members of an enumeration." Your declaration does not
declare any of those.

 

[JoseMariaSola]

It's a constraint violation, which requires a diagnostic from any
conforming implementation.


If you asked it to try to conform to the standard, then yes.


It's in 6.7p2: "A declaration shall declare at least a declarator (other
than the parameters of a function or the members of a structure or union),
a tag, or the members of an enumeration." Your declaration does not
declare any of those.

Thanks!