Re: GTK signals question.

[Chris Moller <moller mollerware com>]

On 03/05/14 12:07, Chris Vine wrote:
> On Wed, 05 Mar 2014 09:44:48 -0500
> Chris Moller <moller mollerware com> wrote:
> > I was actually writing that testcase when I found a correlation: I'm
> > using gcc and my callbacks were nested functions.  Pull the callbacks
> > out and make them normal, top-level, functions, and it all works even
> > without no blocking of any kind.  So, if this is a bug at all, I
> > suppose it could be a compiler bug.
> Your question contained references to GTK+'s C interface.  If that
> means that you are using C or C++ for your program, those languages do
> not have a syntax for nested functions, so what you say does not really
> make sense.  If you are simulating them in C++ using static methods of a
> nested struct, in C++98 you have undefined behaviour if you try to use
> them as a callback, because static member functions of classes with
> local scope have no linkage (this follows because §3.5/5 of the standard
> provides that a member function of class scope has external linkage if
> the name of the class has external linkage, which it doesn't in the
> case of local nested structs, and §3.5/8 provides that "Names not
> covered by these rules have no linkage").
>
> So it is most likely a misunderstanding on your part rather than a
> compiler bug, but you would need to post your code to be sure.

gcc supports nested functions as an extension to standard C.  I tend to 
use them a lot because they operate within the stack frame of the 
enclosing function, thereby minimising the amount of information you 
have to pass.  This is especially valuable in GTK callbacks where you 
can only pass one pointer/int.

> Chris