On Mon, Feb 18, 2013 at 9:38 AM, Charles Forsyth <charles.fors...@gmail.com>wrote:
> On 18 February 2013 13:02, Comeau At9Fans <comeauat9f...@gmail.com> wrote: > >> seems to be doing is setting up allowing the call to compile and once >> that is satisfied then the subsequent definition "has" to match it, as >> perhaps a way to do type punning. > > > No, the compiler is simply applying scope rules. Without that inner > declaration explicitly overriding the outer declaration--whether static or > extern is used-- > it will not compile (eg, if you put "static void fn(Outer*);" or "extern > void fn(Outer*);" and remove static from fn in the file scope). > > The behaviour is undefined in ANSI C if two declarations that refer to the > same object or function do not have compatible types > (normally, you're protected by another rule that you can't have > incompatible declarations *in the same scope*). > > ANSI C does, however, forbid the inner static declaration (which surprised > me) > "The declaration of an identifier for a function that has block scope > shall have no explicit storage-class specifier other than extern." (6.7.1) > We're probably saying the same thing. As you say ANSI C forbids it hence my comment about normally a diagnostic from a so-called mainstream compiler. And as you say without a declaration it would not compile either. The declaration should normally be in global scope (it could have been), which would have also produced a diagnostic since Inner/Outer don't match. That leaves the declaration where Eric showed it, which the Plan 9 compiler obviously allowed. As you note the net effect is it's undefined (if we're using ANSI C as the metric) hence created a kind of type pun (even if the original code did it as a mistake). -- Greg Comeau / 4.3.10.1 with C++0xisms now in beta! Comeau C/C++ ONLINE ==> http://www.comeaucomputing.com/tryitout World Class Compilers: Breathtaking C++, Amazing C99, Fabulous C90. Comeau C/C++ with Dinkumware's Libraries... Have you tried it?
