Re: [Bug-ddrescue] [PATCH 3/5] io: Add missing prototype

[Antonio Diaz Diaz]

Rosen Penev wrote:
> > > > > +extern "C" void sighandler( int signum );
> > > > >     extern "C" void sighandler( int signum )
> > > > >       { if( signum_ == 0&&    signum>    0 ) signum_ = signum; }
> > > >
> > > > There is nothing missing here. A function definition is a function
> > > > declaration in which the body of the function is presented. Therefore
> > > > there is no need to declare the function twice.
> > >
> > > My understanding here is that this function needs to be static or
> > > declared separately. static cannot be used with extern so I went for
> > > the other option.
> >
> > Why does it need to be static or declared separately? I can see nothing
> > in the C++ standard requiring that. AFAICT, all that is required is that
> > the function is declared before being used, and a definition is also a
> > declaration.
>
> In the case of static, it's a huge help to the compiler in terms of
> figuring out if the function is used only in the file and as a result,
> inlining the function which reduces the overall size.

But this function can't be inlined because it is a signal handler whose 
address must be passed to sigaction.

> -Wmissing-prototypes is not valid for C++ but is valid for C.

But the fact that 'sighandler' has "C" linkage does not turn the whole 
file into C. The C++ standard applies.

> -Wmissing-prototypes is not valid for C++ but is valid for C. From the GCC docs:
>
> Warn if a global function is defined without a previous prototype
> declaration. This warning is issued even if the definition itself
> provides a prototype. Use this option to detect global functions that
> do not have a matching prototype declaration in a header file. This
> option is not valid for C++ because all function declarations provide
> prototypes and a non-matching declaration declares an overload rather
> than conflict with an earlier declaration. Use -Wmissing-declarations
> to detect missing declarations in C++.

And just below that:

'-Wmissing-declarations'
Warn if a global function is defined without a previous declaration.  Do 
so even if the definition itself provides a prototype.  Use this option 
to detect global functions that are not declared in header files.  In C, 
no warnings are issued for functions with previous non-prototype 
declarations; use '-Wmissing-prototypes' to detect missing prototypes. 
In C++, no warnings are issued for function templates, or for inline 
functions, or for functions in anonymous namespaces.

Note that 'sighandler' is inside an anonymous namespace.


Best regards,
Antonio.