typedef - c++

In article <1185271469.646051.298710@d55g2000hsg.googlegroups.com>,
tjark.weber says...
> Hi,
>
> just wondering: are there any relevant differences between
>
> struct S { /* ... */ };
>
> and
>
> typedef struct { /* ... */ } S;

Using the first form, the class name is defined (but incomplete) inside
of the class definition, so you can use it anywhere an incomplete type
is allowed. For an obvious example, creating a pointer:

struct S {
S *s;
};

works, but with the typedef:

typedef struct {
S *s;
} S;

it doesn't -- in this case, 'S' isn't a defined symbol inside of the
class definition.

--
Later,
Jerry.

The universe is a figment of its own imagination.

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Tjark Weber wrote:
> Hi,
>
> just wondering: are there any relevant differences between
>
> struct S { /* ... */ };
>
> and
>
> typedef struct { /* ... */ } S;
>
> ?

In addition to Jerry Coffin's answer;

In the former case, you can use the name S as in:

struct S s;

but you can't in the latter case, and you can only use it as in:

S s;

--
Seungbeom Kim

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On Jul 25, 4:24 am, Tjark Weber <tjark.we...> wrote:
> just wondering: are there any relevant differences between
> struct S { /* ... */ };
> and
> typedef struct { /* ... */ } S;

Hi Tjark,

Similar to Jerry and Seungbeom's observations, as your typedef method
creates an alias to an anonymous struct, you'll find:
1) GNU preprocessor __PRETTY_FUNCTION__ contains "<anonymous struct>"
2) some debuggers may lack an information structure name (though some
tools (e.g. g++/gdb) coordinate use of the typedef name)
3) you can't define constructors and destructors (because their name
must match the structure's)
4) when struct is used, the identifier 'S' exists in a struct-specific
naming space, such that you could potentially define some other thing
called 'S', such as a function, without getting a compilation error.
For example: struct S; void S(int);


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On Jul 24, 8:24 pm, Tjark Weber <tjark.we...> wrote:
> Hi,
>
> just wondering: are there any relevant differences between
>
> struct S { /* ... */ };
>
> and
>
> typedef struct { /* ... */ } S;
>
> ?
>
Another couple of differences:
- You can't define a constructor in the latter form.
- The latter is not idiomatic C++ (I would reject it in code review
unless it was code being shared between C and C++).


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