I want to add some safety checks for "not null" for
this I would like to have a macro that checks if
some variable is an array and not a pointer.

#define IS_ARRAY(A) _Static_assert(sizeof(A)/sizeof(A[0]) > 1, "not array")

int main() {

char a[] = "abc";
char* b = "123";

IS_ARRAY(a); //OK
IS_ARRAY(b); //SHOULD FAIL
}

any ideas?

Or check if is pointer.. also helps.

On Friday, May 7, 2021 at 11:34:09 AM UTC-3, Thiago Adams wrote:
> I want to add some safety checks for "not null" for
> this I would like to have a macro that checks if
> some variable is an array and not a pointer.

Something I would like to emulate is the check for

void f(char s[static 5]) { }

In this case I think I could use:

void f(char s[5]) {
printf("%s", s);
}

#define F(S) _Static_assert(sizeof(S)/sizeof(S[0]) >= 5, "too small"); f(S)

int main() {

char a[] = "abcde";
//char* b = "123";
F(a);
}

But also the check for null would be for something like:

void F(struct X* p);

On 07/05/2021 16:33, Thiago Adams wrote:
> I want to add some safety checks for "not null" for
> this I would like to have a macro that checks if
> some variable is an array and not a pointer.
>
>
> #define IS_ARRAY(A) _Static_assert(sizeof(A)/sizeof(A[0]) > 1, "not array")
>
> int main() {
>
> char a[] = "abc";
> char* b = "123";
>
> IS_ARRAY(a); //OK
> IS_ARRAY(b); //SHOULD FAIL
> }
>
> any ideas?
>
> Or check if is pointer.. also helps.
>

I am fairly sure there is a macro of this sort used in the Linux kernel,
but I am afraid I can't remember what it is, and I don't have the time
to look for it just now. But with that hint and a bit of googling,
maybe you'll find it. (Of course, it could be that it uses "typeof" or
some other gcc extension.)

On Friday, May 7, 2021 at 1:58:09 PM UTC-3, David Brown wrote:
> On 07/05/2021 16:33, Thiago Adams wrote:
> > I want to add some safety checks for "not null" for
> > this I would like to have a macro that checks if
> > some variable is an array and not a pointer.
> >
> >
> > #define IS_ARRAY(A) _Static_assert(sizeof(A)/sizeof(A[0]) > 1, "not array")
> >
> > int main() {
> >
> > char a[] = "abc";
> > char* b = "123";
> >
> > IS_ARRAY(a); //OK
> > IS_ARRAY(b); //SHOULD FAIL
> > }
> >
> > any ideas?
> >
> > Or check if is pointer.. also helps.
> >
> I am fairly sure there is a macro of this sort used in the Linux kernel,
> but I am afraid I can't remember what it is, and I don't have the time
> to look for it just now. But with that hint and a bit of googling,
> maybe you'll find it. (Of course, it could be that it uses "typeof" or
> some other gcc extension.)

I found some links and I create this

#define IS_POINTER(P) (void (*)(void**)){0}(&(P))

int main() {

char x[10];
IS_POINTER(x);//warning as expected
//warning C4047: 'function': 'void **' differs in levels of indirection from 'char (*)[10]'

char* p;
IS_POINTER(p);//OK
}

This macros gives us a warning if P is not a pointer.
Taking the address of a variable if it is a pointers it gives **.

no success for array yet...

#define IS_ARRAY(P) _Static_assert(sizeof(P) > sizeof(void*) || sizeof(P)/sizeof(P[0]) < 4, "not array")

int main() {
char x[] = "ghdd";
IS_ARRAY(x);

char* p;
IS_ARRAY(p);
}

This fails only if array has exactly 4 elements

Thiago Adams <thiago.adams@gmail.com> writes:
> I want to add some safety checks for "not null" for
> this I would like to have a macro that checks if
> some variable is an array and not a pointer.
>
>
> #define IS_ARRAY(A) _Static_assert(sizeof(A)/sizeof(A[0]) > 1, "not array")
>
> int main() {
>
> char a[] = "abc";
> char* b = "123";
>
> IS_ARRAY(a); //OK
> IS_ARRAY(b); //SHOULD FAIL
> }
>
> any ideas?
>
> Or check if is pointer.. also helps.

The condition is incorrect.
sizeof(a) is 4; sizeof(a[0]) is 1.
sizeof(b) is likely 8 (sizeof(char*)); sizeof(b[0]) is 1, so the
condition is true even though b is a pointer.

And if p is pointer, sizeof(p) could be equal to sizeof(p[0]) by coincidence.

(And you'd want to parenthesize all occurrences of A in the macro
definition.)

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips Healthcare
void Void(void) { Void(); } /* The recursive call of the void */

On 07/05/2021 18:57, David Brown wrote:
> On 07/05/2021 16:33, Thiago Adams wrote:
>> I want to add some safety checks for "not null" for
>> this I would like to have a macro that checks if
>> some variable is an array and not a pointer.
>>
>>
>> #define IS_ARRAY(A) _Static_assert(sizeof(A)/sizeof(A[0]) > 1, "not array")
>>
>> int main() {
>>
>> char a[] = "abc";
>> char* b = "123";
>>
>> IS_ARRAY(a); //OK
>> IS_ARRAY(b); //SHOULD FAIL
>> }
>>
>> any ideas?
>>
>> Or check if is pointer.. also helps.
>>
>
>
> I am fairly sure there is a macro of this sort used in the Linux kernel,
> but I am afraid I can't remember what it is, and I don't have the time
> to look for it just now. But with that hint and a bit of googling,
> maybe you'll find it. (Of course, it could be that it uses "typeof" or
> some other gcc extension.)
>

These are from Zephyr, and are probably the same as the Linux kernel.
It turns out it uses typeof /and/ another gcc extension.

/** @brief 0 if @p cond is true-ish; causes a compile error otherwise. */
#define ZERO_OR_COMPILE_ERROR(cond) ((int) sizeof(char[1 - 2 * !(cond)])
- 1)

#define IS_ARRAY(array) \
ZERO_OR_COMPILE_ERROR( \
!__builtin_types_compatible_p(__typeof__(array), \
__typeof__(&(array)[0])))