igb@fulcrum.bt.co.uk (Ian G Batten) (04/08/91)
C News, amongst other things, has declarations of ``extern int foo;'' in either a header or towards the top of a file, and later has ``static int foo;''. An example is found in libc/datetok.c or libc/getdate.y. This compiles happily with V.2, V.3, V.4, SunOS 4.0, gcc -traditional or gcc in ansi mode. In the last case it generates a warning about redeclaration. On an IBM RS/6000 (it wasn't my idea) in generates an identifier redeclared error and exits during compilation. Lint on an RS/6000 merely reports the redeclaration as a warning. This is great: a C compilers that objects to code lint merely warns about. Can anyone quote chapter and verse as to the legality of this? As I want to compile C news, can anyone suggest a workaround? We've had the RS/6000 for a few days now and kids, I'll now believe any story, however bad... ian
ian@airs.UUCP (Ian Lance Taylor) (04/09/91)
In article <^R+_H3-@uzi-9mm.fulcrum.bt.co.uk> igb@fulcrum.bt.co.uk (Ian G Batten) writes: >C News, amongst other things, has declarations of ``extern int foo;'' in >either a header or towards the top of a file, and later has ``static int >foo;''. > >Can anyone quote chapter and verse as to the legality of this? The ANSI C standard 3.1.2.2: ``... If the declaration of a file scope identifier for an object or a function contains the storage-class specifier *static*, the identifier has internal linkage. If the declaration of an identifier for an object or a function contains the storage-class specifier *extern*, the identifier has the same linkage as any visible declaration of the identifier with file scope. If there is no visible declaration with file scope, the identifier has external linkage. ... If, within a translation unit, the same identifier appears with both internal and external linkage, the behavior is undefined.'' So in the case you mention, the behavior is undefined. This means that according to the standard, the compiler can do anything it pleases, specifically including ``terminating a translation.'' Of course, in this particular case that's pretty tacky. Still, in the long run it would probably be better to change the code (I have no idea what that would involve). -- Ian Taylor airs!ian@uunet.uu.net uunet!airs!ian First person to identify this quote wins a free e-mail message: ``But this machine chews all kinds of paper into a thick porridge that no chemist in the world, however skilled a criminal he may be, can read.''
henry@zoo.toronto.edu (Henry Spencer) (04/10/91)
In article <1991Apr9.055250.24257@world.std.com> geoff@world.std.com (Geoff Collyer) writes: >Henry's opinion (I hope I'm not misquoting him) is that there are certain >cases that ANSI doesn't cover either (forward static arrays, as I recall). Forward static arrays of unspecified size are the problem. For those, there simply is no portable way to write a forward declaration, and we're simply going to have to avoid doing this. For everything else, the problem is not unsolvable, merely awkward. Old compilers won't take static forward declarations at all, while new ones won't take extern forward declarations for static objects. The choice is between avoiding forward declarations entirely, using a macro so you can make them extern or static as required, or just giving up and making the objects extern. These are all somewhat distasteful. While we do intend to be ANSI compatible, our development systems have historically used old compilers, and it will be quite a while before the last lingering glitches get sorted out. -- "The stories one hears about putting up | Henry Spencer @ U of Toronto Zoology SunOS 4.1.1 are all true." -D. Harrison| henry@zoo.toronto.edu utzoo!henry
sanders@cactus.org (Tony Sanders) (04/16/91)
In article <^R+_H3-@uzi-9mm.fulcrum.bt.co.uk> igb@fulcrum.bt.co.uk (Ian G Batten) writes: >On an IBM RS/6000 (it wasn't my idea) in generates an identifier >redeclared error and exits during compilation. To work around the problem you can simply change the name of the thing so it doesn't conflict with anything else (if it's called foo rename it to my_foo) and then remove the "static". Ugly but it works. -- sanders@cactus.org I am not an IBM representative, I speak only for myself. I have a wonderful proof that emacs is better than vi, only this .sig is too small to contain it.