implicit type conversions

[buda]

Let me see if I got this :)
1. I know the rules for type conversions in arithmetic expressions
2. I know that an implicit type conversion is done at assignment, so
float x = 1.23;
int t = (int) x;
is equivalent to
int t = x;
(could the latter produce a warning on some complier?)
3. I know that implicit conversions take place with function arguments, but
am a bit shaky here. I suppose that passing a char to a function accepting
int or long will always work, and those sort of conversions seem to make
sense. But what sort of things won't work here? For example, the FAQ says
that the NULL pointer *must* be cast to the appropriate type when sent to a
function as an argument (so, for example, time(NULL) is incorrect, and
time( (time_t *) NULL) is correct?), which seems to indicate that
conversions from (void *) to (some_type *) in function argument lists need
not be (isn't) implicit. If someone would clarify this, I'd be most grateful
(like which sort of things cause warnings, which need be cast and the like).

Thank you.

[Sam Dennis]

Old Wolf wrote:

void put_strings(cha r *f1, ...)

If called with: put_strings("fo o", NULL); would cause UB even if
NULL is (void *)0.

Not in this case (pointers to void and `a character type' (normally
read as `all the character types') have identical representations ),
but it's certainly a concern for pointers to other types, functions
in particular.

--
++acr@,ka"

[Dan Pop]

In <sl************ ****@ID-227112.user.uni-berlin.de> Sam Dennis <sa*@malfunctio n.screaming.net > writes:

Old Wolf wrote:

void put_strings(cha r *f1, ...)

If called with: put_strings("fo o", NULL); would cause UB even if
NULL is (void *)0.

Not in this case (pointers to void and `a character type' (normally
read as `all the character types') have identical representations ),

Identical representation means exactly zilch in context. What you
need is identical argument passing mechanisms and the standard provides
no normative guarantees about that.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[Sam Dennis]

Dan Pop wrote:

In <sl************ ****@ID-227112.user.uni-berlin.de> Sam Dennis <sa*@malfunctio n.screaming.net > writes:

Old Wolf wrote:

void put_strings(cha r *f1, ...)

If called with: put_strings("fo o", NULL); would cause UB even if
NULL is (void *)0.

Not in this case (pointers to void and `a character type' (normally
read as `all the character types') have identical representations ),

What you need is identical argument passing mechanisms and the
standard provides no normative guarantees about that.

That's probably true, but I doubt that there's any conforming
implementation in existence that does not follow the footnote
strongly suggesting this reading.

--
++acr@,ka"

[Dan Pop]

In <sl************ ****@ID-227112.user.uni-berlin.de> Sam Dennis <sa*@malfunctio n.screaming.net > writes:

Dan Pop wrote:

In <sl************ ****@ID-227112.user.uni-berlin.de> Sam Dennis <sa*@malfunctio n.screaming.net > writes:

Old Wolf wrote:
void put_strings(cha r *f1, ...)

If called with: put_strings("fo o", NULL); would cause UB even if
NULL is (void *)0.

Not in this case (pointers to void and `a character type' (normally
read as `all the character types') have identical representations ),

What you need is identical argument passing mechanisms and the
standard provides no normative guarantees about that.

That's probably true, but I doubt that there's any conforming
implementati on in existence that does not follow the footnote
strongly suggesting this reading.

Are they still maintaining the DS9k?

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[Dave Thompson]

On 4 Jun 2004 10:37:28 GMT, Da*****@cern.ch (Dan Pop) wrote:

In <sl************ ****@ID-227112.user.uni-berlin.de> Sam Dennis <sa*@malfunctio n.screaming.net > writes:

Old Wolf wrote:

void put_strings(cha r *f1, ...)
[ and using va_arg to get as char* ]
If called with: put_strings("fo o", NULL); would cause UB even if
NULL is (void *)0.

Not in this case (pointers to void and `a character type' (normally
read as `all the character types') have identical representations ),

Identical representation means exactly zilch in context. What you
need is identical argument passing mechanisms and the standard provides
no normative guarantees about that.

It does in C99: 7.5.1.1p2 for va_arg, and 6.5.2.2p6 for (wholly)
unprototyped/K&R1 definitions. Also for (the shared range of)
corresponding signed and unsigned integers. Presumably if any
implementor wasn't already doing these and wasn't willing to change
they would have objected.

- David.Thompson1 at worldnet.att.ne t

[Dan Pop]

In <5a************ *************** *****@4ax.com> Dave Thompson <da************ *@worldnet.att. net> writes:

On 4 Jun 2004 10:37:28 GMT, Da*****@cern.ch (Dan Pop) wrote:

In <sl************ ****@ID-227112.user.uni-berlin.de> Sam Dennis <sa*@malfunctio n.screaming.net > writes:

>Old Wolf wrote:
>> void put_strings(cha r *f1, ...)
>> [ and using va_arg to get as char* ]
>> If called with: put_strings("fo o", NULL); would cause UB even if
>> NULL is (void *)0.
>
>Not in this case (pointers to void and `a character type' (normally
>read as `all the character types') have identical representations ),

Identical representation means exactly zilch in context. What you
need is identical argument passing mechanisms and the standard provides
no normative guarantees about that.

It does in C99: 7.5.1.1p2 for va_arg, and 6.5.2.2p6 for (wholly)
unprototyped/K&R1 definitions. Also for (the shared range of)
correspondin g signed and unsigned integers. Presumably if any
implementor wasn't already doing these and wasn't willing to change
they would have objected.

This is correct, if you fix the va_arg reference. I had the printf case
in mind, where 7.15.1.1p2 doesn't apply.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de