In article <3ulsif$fnv@highway.LeidenUniv.nl> vosse@ruls41.LeidenUniv.nl (Theo Vosse) writes:
>I'm having some problems with my compiler (CodeWarrior/6 for
>the Macintosh). If I write in a C++ source file
>
>extern "C"
>{
>#include "somefile.h"
>}
>
>and write in "somefile.h" this:
>
>typedef struct X *X;
>
>the compiler says that the identifier X has already been
>declared, and that this construct is illegal.
>
>Is this correct?

The construct is not valid.  Let's consider

typedef struct X *X;

by itself without the extern "C" wrapper.  In C++, you're allowed to have
a tag name (class, struct, union, or enum) and a non-type name coexisting
in a single scope under the C compatibility "struct hack."  You're also
allowed to declare a typedef name that matches the struct/union/class
defined:

typedef struct X { ... } X;

However, the case you write is neither of those.  It's valid in C, but
not in C++.  Putting extern "C" around it doesn't make it any more valid
in C++; as you say, the effect of extern "C" is only on linkage.  It
doesn't say that what's inside is C code.

Steve Adamczyk

Hi,

I'm having some problems with my compiler (CodeWarrior/6 for
the Macintosh). If I write in a C++ source file

extern "C"
{
#include "somefile.h"
}

and write in "somefile.h" this:

typedef struct X *X;

the compiler says that the identifier X has already been
declared, and that this construct is illegal.

Is this correct? According to a support engineer at MetroWerks
(the manufacturer):

The string-literal indicates the required linkage.  The meaning of the
string-literal is implementation-defined.  Every implementation shall
provide for linkage to functions written in the C programming language,
"C", and linkage to C++ functions, "C++".  Default linkage is "C++"....

All references in the draft to 'extern "C"' involve linkage only, and not
general syntax.  The ARM takes a similar stance.

Can anyone confirm this? Do I have to rewrite my code?

Thanks in advance...

--
 Theo Vosse
 ----------
 Unit for Experimental Psychology
 University of Leiden
 The Netherlands