--- James Dennett <[EMAIL PROTECTED]> wrote:
> Joe Wilson wrote:
> > The proposed expression ((sqlite3_destructor_type)-1) is equivalent to
> > ((void(*)(void *))-1). They are interchangable.
>
> Not in C++. The difference being linkage; with the typedef declared in
> an extern "C" block, the type is something that can't be written
> directly.
Now I understand your confusion. SQLite is a C. All its API definitions in
sqlite3.h and its function pointers are obviously C-based. So to avoid these
warnings related to using SQLITE_TRANSIENT (or SIG_ERR for that matter)
in your C++ code, your C++ implementation file must do the following:
// example.cpp
#include "sqlite3.h"
extern "C" {
void example(sqlite3_context* c, const char* b, int n) {
sqlite3_result_text(c, b, n, SQLITE_TRANSIENT);
}
// you can even put class member function implementations in here
// i.e., void Foo::bar() {...}
// without affecting their C++ linkage.
}
You'll find that it compiles in Sun C++ 5.8 2005/10/13 without warnings
using the unmodified sqlite3.h file.
The C++ code does not need the proposed typedef to handle SQLITE_TRANSIENT,
although if it were added to sqlite3.h it would not do any harm, and you
might be able to avoid the extern "C" block around your sqlite-related
function implementations.
> > #define SIG_IGN (void(*)(int))1
> > #define SIG_ERR (void(*)(int))-1
> >
> > Such C code is grandfathered in C++. If it wasn't you wouldn't be able
> > to do any UNIX systems programming in C++.
>
> It's not portable C, and it's not portable C++. It does seem to be
> blessed by POSIX, but POSIX is just a subset of the much larger range of
> platforms supported by ISO/ANSI C and C++.
In your original question you asked:
On a related but separate note, is there any standard that guarantees
that casting -1 to a function pointer type is reasonably portable?
And yes, it is reasonably portable as shown by every UNIX variant that
must deal with POSIX and every major C++ compiler vendor, as a consequence.
That's good enough for me. It may or may not be blessed by the C++ standard,
but if you can dig up a modern popular C++ compiler that does not work with
such code, I'd be surprised.
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