On 06/14/2018 04:52 PM, Joseph Myers wrote:
On Thu, 14 Jun 2018, Martin Sebor wrote:
The standard says FILE is a type so I don't think it can
be a macro that expands to something other than a type
named FILE. The spec doesn't prevent programs from
#undef-ing FILE so implementations cannot define it as
one and rely on it staying defined(*). So even if FILE
is a macro, it still (also) has to be an identifier of
a type with that name.
You can #undef it and then use FILE yourself as a block-scope identifier.
I don't think it's at all clear that you can #undef it and then use FILE
and expect to get the semantics of the standard type FILE (unlike for
standard functions).
I'm not sure I know what you mean here. Say we have:
#include <stdio.h>
#undef FILE
void f (void)
{
extern FILE *fp;
fprintf (fp, "");
}
Are you saying it's not clear that this is well-defined?
FILE can be a typedef for some other type, but I'm not sure
I see how that creates a problem. fileptr_type_node could
refer to anything at all (even ptr_type_node) initially and
be set to refer to the first file-scope type or typedef
named FILE seen in a translation unit. It shouldn't matter
if that happens to be a type that's unrelated to the stdio
FILE. Is there something I'm missing that makes this approach
not feasible? (If I'm wrong about FILE being a macro to some
unrelated name then that would sink this idea.)
Setting the fileptr_type_node object to point to a different node would
have no effect on the pointers to that particular node nested within
various function types. You'd need to modify lots of pointers within
those function types, or reconstruct those function types and change the
types of the built-in functions.
Yeah, that sound like a lot of fiddling. I suppose what
I should have said is that whatever fileptr_type_node pointed
to would be modified in place to refer to the new node. I.e.,
initialize it to some placeholder kind of an object (a copy
of ptr_type_node like in the C++ FE) and modify the object
once a definition were seen. Would that work?
Martin
