andrew@alice.UUCP (Andrew Hume) (09/09/90)
In article <11305@alice.UUCP>, andrew@alice.UUCP (Andrew Hume) writes:
~
~ the following C fragment fails with a strict ANSI compiler (lcc)
~ but compiles with sloppy ones (e.g. gcc):
~
~ typedef int (*fn)(struct x *);
~ extern int fn1(struct x *);
~ extern fn *fp = fn1;
~
~ the ostensible reason is that the two struct x's are different
~ (or at least, have different scopes).
~ this may be technically correct but is just wrong.
~ can anyone explain why anyone would want this batshit behaviour?
let me correct an error and clarify; the fragment contains a bug - it should be
typedef int (*fn)(struct x *);
extern int fn1(struct x *);
extern fn fp = fn1;
i understand technically (i think) what is going on.
the first line introduces a type struct x which goes away
at the end of the prototype and can never be used again.
my question is why didn't ANSI do what C++ does here and export
the type up to file scope?
andrew@research.att.comandrew@alice.UUCP (Andrew Hume) (09/10/90)
just in case i miscommunicated, when i said sloppy ansi c compilers (gcc), i referred to its default behaviour. otherwise, its warning messages seem exemplary: xx.c:1: warning: `struct x' declared inside parameter list xx.c:1: warning: its scope is only this definition or declaration, xx.c:1: warning: which is probably not what you want. xx.c:2: warning: `struct x' declared inside parameter list xx.c:3: warning: `fp' initialized and declared `extern' xx.c:3: warning: initialization between incompatible pointer types sorry for any unintended denigration of GNU's gcc.
scjones@thor.UUCP (Larry Jones) (09/10/90)
In article <11312@alice.UUCP>, andrew@alice.UUCP (Andrew Hume) writes: > typedef int (*fn)(struct x *); > extern int fn1(struct x *); > extern fn fp = fn1; > i understand technically (i think) what is going on. > the first line introduces a type struct x which goes away > at the end of the prototype and can never be used again. > my question is why didn't ANSI do what C++ does here and export > the type up to file scope? Because the committee got tired of C being an almost block structured language -- the exceptions are very difficult to describe concisely and completely -- so they tried to tighten up the structuring wherever possible. Since prototypes were a committee invention, they got tight scoping rules. Making exceptions to the rules when it's convenient to do so may seem like a good idea at the time, but it just causes a great deal of pain and aggravation when you have to explain just exactly when the exceptions occur and what they do. ---- Larry Jones UUCP: uunet!sdrc!thor!scjones SDRC scjones@thor.UUCP 2000 Eastman Dr. BIX: ltl Milford, OH 45150-2789 AT&T: (513) 576-2070 You can never really enjoy Sundays because in the back of your mind you know you have to go to school the next day. -- Calvin