gcc question about the embedded type definitions

gcc question about the embedded type definitions

[Wei ZHANG]

Hi,

I have a question on embedded type definitions.

If in a structure definition, another type is defined. e.g.

typedef struct S1 {
struct S2 {
int a;
}
} S1;

is the data type S2 visible outside S1? Originally i think it is not 
visible outside.

But in gcc, I can declare a varible of type struct S2, and operate on 
it. e.g.:

S2 b;
b.a = 100;
printf("result = %d\n", b.a);

That implies the name of the structure type S2 must be unique in the C 
file. Am I right? Can anyone elaborate on this? Thanks!

Best Regards,
Zhang Wei

Re: gcc question about the embedded type definitions

[Nathan Sidwell]

Wei ZHANG wrote:
> Hi,
> 
> I have a question on embedded type definitions.
> 
> If in a structure definition, another type is defined. e.g.
> 
> typedef struct S1 {
> struct S2 {
> int a;
> }
> } S1;
> 
> is the data type S2 visible outside S1? Originally i think it is not 
> visible outside.

in C it is visible, in C++ it is not.
in C it declares a field of the outer struct, in C++ it declares
a nested member.

Your example is neither C not C++ though, as it is missing at least a
semi colon.

nathan

-- 
Nathan Sidwell    ::   http://www.codesourcery.com   ::     CodeSourcery LLC
nathan@codesourcery.com    ::     http://www.planetfall.pwp.blueyonder.co.uk

Re: gcc question about the embedded type definitions

[Serge Fukanchik]

Nathan Sidwell wrote:
> in C it is visible, in C++ it is not.
?! In C++ all members of `struct' are public by default
and hence fully accessible. You have to explicitly say `private:'.

On the other side all members of `class' are private by default.
You can not access them unless you say `public:'
---
Serge

Re: gcc question about the embedded type definitions

[Nathan Sidwell]

Serge Fukanchik wrote:
> Nathan Sidwell wrote:
> 
>> in C it is visible, in C++ it is not.
> 
> ?! In C++ all members of `struct' are public by default
> and hence fully accessible. You have to explicitly say `private:'.

you have to qualify their names -- they are not visible in
the global namespace. The question was about their visibility
not their accessibility.


nathan

-- 
Nathan Sidwell    ::   http://www.codesourcery.com   ::     CodeSourcery LLC
nathan@codesourcery.com    ::     http://www.planetfall.pwp.blueyonder.co.uk