Re: Casting int'** to 'const int * const * const' dosn't work, why?

Jonas.Holmsten@xxxxxxxxx wrote:
Hello

I'm porting some C++ stuff to C and having problem to get it through
gcc.
Here is a condensed version of the problem:

void foo(const int * const * const ptr)
{}

main()
{
int i = 5;
int *ptr = &i;

foo(&ptr);
}

The warning is:
warning: passing arg 1 of `foo' from incompatible pointer type.

Can't C implicit cast a int** to 'const int * const * const'? (it
works fine in C++)

This is really a question for Chris Torek...

Here is a simpler example:

$ cat const_cast.c
int main(void)
{
int **ppi;
const int * const *pcpci;

pcpci = ppi;


return 0;
}
$ cc -ansi -pedantic -Wall -W const_cast.c
const_cast.c: In function âmainâ:
const_cast.c:7: warning: assignment from incompatible pointer type

which requires a diagnostic in C (but perhaps not in C++, since no const'ness is lost).

In C, two types are compatible if they are the same type (not only if). A type qualifier (like const), change the type. When it comes to pointer types, they are compatible, if they point to compatible types.


--
Tor <torust [at] online [dot] no>
.

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