Re: server/fd.c: Prevent using uninitialized pointers

[Henri Verbeet]

2009/6/30 Daniel Santos :
> Some pointers are getting used prior to initialization.  It would appear that the current compilers are initializing them to zero or we've been lucky.

No, the C standard specifies that these are initialized to NULL, since
they have static storage duration.

server/fd.c: Prevent using uninitialized pointers

[James McKenzie]

Henri Verbeet wrote:
> 2009/6/30 Daniel Santos :
> > Some pointers are getting used prior to initialization.  It would appear that the current compilers are initializing them to zero or we've been lucky.
>
> No, the C standard specifies that these are initialized to NULL, since
> they have static storage duration.

We are assuming that the c compilers are following the standard.  I was
told a long time ago, 1994 to be exact, that if we want to insure that a
variable has a certain value to initialize it to that value.  This
applies if we want a zero or a NULL.

[code]

int a = 0;
char b = NULL;
bool c = TRUE;

[/code]

Without this, we cannot assume anything.

James McKenzie

server/fd.c: Prevent using uninitialized pointers

[Vitaliy Margolen]

James McKenzie wrote:
> [code]
>
> int a = 0;
> char b = NULL;
> bool c = TRUE;
>
> [/code]
>
> Without this, we cannot assume anything.

Static variables are different. They are always initialized to 0. In your
example you show regular variables only. Their initial value is not defined.

Vitaliy.

server/fd.c: Prevent using uninitialized pointers

[James McKenzie]

Vitaliy Margolen wrote:
> James McKenzie wrote:
> > [code]
> >
> > int a = 0;
> > char b = NULL;
> > bool c = TRUE;
> >
> > [/code]
> >
> > Without this, we cannot assume anything.
>
> Static variables are different. They are always initialized to 0. In your
> example you show regular variables only. Their initial value is not defined.

Correct.  I was making the assumption that the discussion was not about
static variables.  Static variables are always initialized:

static int a;

will be zero

static char b;

will be NULL

static bool c;

will be set to false (0) unless zero is defined as TRUE.

However, if you want a particular result, it is always best to
initialize the variables you are going to use.

James McKenzie

server/fd.c: Prevent using uninitialized pointers

[Frédéric Delanoy]

On 07/04/2009 11:22 PM, James McKenzie wrote:
> Vitaliy Margolen wrote:
> > James McKenzie wrote:
> > > [code]
> > >
> > > int a = 0;
> > > char b = NULL;
> > > bool c = TRUE;
> > >
> > > [/code]
> > >
> > > Without this, we cannot assume anything.
> >
> > Static variables are different. They are always initialized to 0. In your
> > example you show regular variables only. Their initial value is not defined.
>
> Correct.  I was making the assumption that the discussion was not about
> static variables.  Static variables are always initialized:
>
> static int a;
>
> will be zero
>
> static char b;
>
> will be NULL

or, more precisely (pedantically) NUL or '\0' (which just happens to be the same as NULL [all bits set to 0] on most (all?) architectures IIRC)

Frédéric

server/fd.c: Prevent using uninitialized pointers

[Henri Verbeet]

2009/7/4 Vitaliy Margolen :
> Static variables are different. They are always initialized to 0. In your

Yes, although perhaps it should be noted that in this particular case
the static storage duration is due to these being global variables,
rather than the static keyword which just specifies internal linking
here. (I.e., if they had external linking the pointers would still be
initialized to NULL.)