Re: Uninitialized SCM variables

[Phil Holmes]

----- Original Message ----- 
From: "Graham Percival" <address@hidden>
To: "Carl Sorensen" <address@hidden>
Cc: "lilypond-devel Development" <address@hidden>
Sent: Wednesday, August 17, 2011 5:48 PM
Subject: Re: Uninitialized SCM variables


> On Wed, Aug 17, 2011 at 05:53:40AM -0600, Carl Sorensen wrote:
> > \On 8/16/11 10:25 PM, "Dan Eble" <address@hidden> wrote:
> >
> > > Is there a reason that these variables in lily/profile.cc don't need to 
> > > be
> > > initialized?  I don't have experience with guile, but it looks 
> > > dangerous.
> >
> > I guess the code in this section relies on the fact that the compiler 
> > will
> > initialize the unitialized value to zero.   Do you believe that is a
> > problem?
>
> Is there a special rule that compilers will always initalize
> uninitialized scheme values to zero?  Because I discovered a
> segfault just yesterday (in a different program) that was because
> of gcc [1] not initalizing a variable to 0.
>
> [1] or rather, the C standard does not specify that an
> uninitalized variable should be set to 0, so I do not blame gcc in
> the least; it was the programmer at fault.
>
> Cheers,
> - Graham

In C-style languages, uninitialised variable are uninitialised and therefore 
have an indeterminant value.  Hence the danger of uninitialised pointers. 
Some other languages do initialise them to 0 - visual basic is an example. 
In more modern languages, (c# is one I'm familiar with) the compile fails if 
a variable is not explicitly initialised.


--
Phil Holmes