Array initialization

[Jo Siffert]

Hi,

I have an array like
Foo **ppArr = new Foo*[ size ];

I would like to check if the array holds a pointer to an object at a
certain index using something like
if ( ppArr[ idx ] == NULL ) { ... }

However, this statement always evaluates to false, as ppArr[ idx ]
always has a value of 0xcdcdcdcd instead of NULL (using VC++ 7).
Do I have to set all fields explicitly to NULL (using something like
UNIX's bzero()) to get this to work?

Thanks,
Jo

[JKop]

Karl Heinz Buchegger posted:

It may be everything. No initialization -> undefined (except in static
cases. God how I hate those exceptions everywhere:

static int i;

i has a value of 0. Even without initialization. It's a leftover from
C)

int* jk;
Mine was a global variable. Global variables get initialized to 0, no?

If so, does a global pointer get initialized to NULL, which may or may not
be 0?
-JKop

[Karl Heinz Buchegger]

JKop wrote:

Karl Heinz Buchegger posted:

It may be everything. No initialization -> undefined (except in static
cases. God how I hate those exceptions everywhere:

static int i;

i has a value of 0. Even without initialization. It's a leftover from
C)
int* jk;

Mine was a global variable. Global variables get initialized to 0, no?

Aehm. ... thinking ... I think the answer is yes. (Not so sure
if I have mixed up static with global variables right now)

I write explicite initializations everywhere and don't have to remember
all those exception rules :-)

If so, does a global pointer get initialized to NULL, which may or may not
be 0?

yes.

Same with double.
Noboby says that the bit pattern for 0.0 equals all bits zero.

--
Karl Heinz Buchegger
kb******@gascad .at

[Andrey Tarasevich]

JKop wrote:

Karl Heinz Buchegger posted:

It may be everything. No initialization -> undefined (except in static
cases. God how I hate those exceptions everywhere:

static int i;

i has a value of 0. Even without initialization. It's a leftover from
C)

int* jk;
Mine was a global variable. Global variables get initialized to 0, no?

If so, does a global pointer get initialized to NULL, which may or may not
be 0?
...

Hmm... You are a bit confused. When it comes to pointer initialization,
NULL acts the same way as literal '0' (or, more precisely, an integral
constant expression that evaluates to zero). So in this context it is
safe to say that NULL _is_ 0.

A pointer of type 'int*' with static storage duration gets implicitly
initialized to null-pointer value (NPV) of type 'int*'. This is not
exactly what NULL is. NULL is universal null-pointer constant (NPC)
(just like literal '0', for example). When NPC gets converted to certain
pointer type 'T*', it turns into NPV of that type. Different pointer
types might use completely different representations for their NPVs.
NPVs are not required to be represented by "all-zeroes" bit pattern.
That's why 'memset' is not guaranteed to produce NPVs in the original
example.

--
Best regards,
Andrey Tarasevich