Odd char string initialization in structs

[gustavo]

I was looking at the Sendmail's source code, and i've got confused
about this kind of initialization:

------------------------
struct prival PrivacyValues[] =
{
{ "public", PRIV_PUBLIC },
{ "needmailhe lo", PRIV_NEEDMAILHE LO },
{ "needexpnhe lo", PRIV_NEEDEXPNHE LO },
{ "needvrfyhe lo", PRIV_NEEDVRFYHE LO },
....
};
------------------------

I'm familiar with char string[] = "foo", but i have no idea what the
above snip of code is doing. Anyone could please explain?

[Keith Thompson]

CBFalconer <cb********@yah oo.com> writes:

Flash Gordon wrote:

edware wrote:

<snip>

struct test_t {
char *a;
int b;
double c;
};

int main(void)
{
struct test_t test = { 0 };
}

Will this initialization set the whole struct to 0,
or just the first member, byte, or something like that?

It will initialise the entire struct so appropriate 0 type values
(null pointers, 0, 0.0 as appropriate). If you initialise any of
it to any value then the rest gets initialised to an appropriate
0 value for the type.

NOT to null pointers. Those you have to handle yourself.

YES to null pointers.

C99 6.7.8p10:

If an object that has automatic storage duration is not
initialized explicitly, its value is indeterminate. If an object
that has static storage duration is not initialized explicitly,
then:

-- if it has pointer type, it is initialized to a null pointer;

-- if it has arithmetic type, it is initialized to (positive or
unsigned) zero;

-- if it is an aggregate, every member is initialized
(recursively) according to these rules;

-- if it is a union, the first named member is initialized
(recursively) according to these rules.

C99 6.7.8p21:

If there are fewer initializers in a brace-enclosed list than
there are elements or members of an aggregate, or fewer characters
in a string literal used to initialize an array of known size than
there are elements in the array, the remainder of the aggregate
shall be initialized implicitly the same as objects that have
static storage duration.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[CBFalconer]

Keith Thompson wrote:

CBFalconer <cb********@yah oo.com> writes:

Flash Gordon wrote:

edware wrote:
<snip>

struct test_t {
char *a;
int b;
double c;
};

int main(void)
{
struct test_t test = { 0 };
}

Will this initialization set the whole struct to 0,
or just the first member, byte, or something like that?

It will initialise the entire struct so appropriate 0 type values
(null pointers, 0, 0.0 as appropriate). If you initialise any of
it to any value then the rest gets initialised to an appropriate
0 value for the type.

NOT to null pointers. Those you have to handle yourself.

YES to null pointers.

C99 6.7.8p10:

If an object that has automatic storage duration is not
initialized explicitly, its value is indeterminate. If an object
that has static storage duration is not initialized explicitly,
then:

-- if it has pointer type, it is initialized to a null pointer;

-- if it has arithmetic type, it is initialized to (positive or
unsigned) zero;

-- if it is an aggregate, every member is initialized
(recursively) according to these rules;

-- if it is a union, the first named member is initialized
(recursively) according to these rules.

C99 6.7.8p21:

If there are fewer initializers in a brace-enclosed list than
there are elements or members of an aggregate, or fewer characters
in a string literal used to initialize an array of known size than
there are elements in the array, the remainder of the aggregate
shall be initialized implicitly the same as objects that have
static storage duration.

Thanks for the correction. I was confusing it with the
'all-bits-zero' case, and in fact I did know better, because I
frequently use that characteristic to control auto-initialization.

--
"If you want to post a followup via groups.google.c om, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson
More details at: <http://cfaj.freeshell. org/google/>
Also see <http://www.safalra.com/special/googlegroupsrep ly/>

[Richard G. Riley]

CBFalconer <cb********@yah oo.com> writes:

It will initialise the entire struct so appropriate 0 type values
(null pointers, 0, 0.0 as appropriate). If you initialise any of
it to any value then the rest gets initialised to an appropriate
0 value for the type.

NOT to null pointers. Those you have to handle yourself.

Then my ISO setting on gnu c doesnt work : because it certainly does
here. Come to think of it, it would be ludicrous if it didn't.

[Robert Gamble]

Richard G. Riley wrote:

CBFalconer <cb********@yah oo.com> writes:

It will initialise the entire struct so appropriate 0 type values
(null pointers, 0, 0.0 as appropriate). If you initialise any of
it to any value then the rest gets initialised to an appropriate
0 value for the type.

NOT to null pointers. Those you have to handle yourself.

Then my ISO setting on gnu c doesnt work : because it certainly does
here. Come to think of it, it would be ludicrous if it didn't.

Right, Chuck acknowleged this a couple of days ago.
However, even if the pointers were not guaranteed to be initialized it
wouldn't mean that a comforming implementation couldn't do so or that
they might not wind up as NULL for some other reason.

Robert Gamble

[Richard G. Riley]

"Robert Gamble" <rg*******@gmai l.com> writes:

Richard G. Riley wrote:

CBFalconer <cb********@yah oo.com> writes:

>> It will initialise the entire struct so appropriate 0 type values
>> (null pointers, 0, 0.0 as appropriate). If you initialise any of
>> it to any value then the rest gets initialised to an appropriate
>> 0 value for the type.
>
> NOT to null pointers. Those you have to handle yourself.
>

Then my ISO setting on gnu c doesnt work : because it certainly does
here. Come to think of it, it would be ludicrous if it didn't.

Right, Chuck acknowleged this a couple of days ago.
However, even if the pointers were not guaranteed to be initialized it
wouldn't mean that a comforming implementation couldn't do so or that
they might not wind up as NULL for some other reason.

Robert Gamble

So he (begrudgingly) did. I apologise for repeating this.