__restrict compiler flag?

I thought the __restrict flag meant that the pointer couldn't be changed...but it can it seems......can somebody tell me clearly what the __restrict flag does?

Code:

---

#include <stdio.h>
#include <al/etl.h>
#include <sfl.h>
 
char *blar( char *__restrict__ sz )
{
        char *s = malloc( NAME_MAX );
        ASSERT( s );
        strncpy( s, "Whoa whoa whoa", NAME_MAX );
        sz = s;
        return sz;
}

int main( void )
{
        char *__restrict hello = "How are you?";
        hello = blar( hello );
        puts( hello );
        free( hello );
        return 0;
}

---

restrict means that the pointer is the only way to access the object to which it points.

Quote:

---

C: A Reference Manual, 5th Edition
Page 94, 4.4.6 Restrict

The type qualifier restrict is new in C99. It may only be used to qualify pointers to
objects or incomplete types, and it serves as a "no alias" hint to the C compiler. This means
that that pointer is, for the moment, the only way to access the object to which it points. Vi-
olating this assumption results in undefined behavior. The phrase "at the moment" means
that in some circumstances within a function or block aliases can be created from the orig-
inal restrict-qualified pointer as long as those aliases are elminated by the end of the func-
tion or block. The C99 standard provides a precise mathematical definition of
restrict, but here are some common situations.

...

---

There are a bunch of examples, but I didn't feel like typing them all up. It doesn't mean the pointer can't be changed. It means that this pointer is the only way to access the current object.

Quzah.

I'm not talking about the restrict type in C99, I'm talking about the __restrict for compilers like gcc. And I can still edit the contents of the pointers =[

Code:

---

#include <stdio.h>
#include <al/etl.h>
#include <sfl.h>

void changeContents( char *__restrict sz )
{
        char *s = sz;
        *s++ = 'S';
        *(sz+1) = 'h';
        *++s = 'i';
        *(sz+3) = 't';
        *(s+2) = ' ';
}

int main( void )
{
        char *__restrict hello = malloc( NAME_MAX );
       
        strncpy( hello, "Hello ma'am!", NAME_MAX );
        changeContents( hello );
       
        puts( hello );
        free( hello );
       
        return EXIT_SUCCESS;
}

---

Code:

---

........  ma'am!

---

The compiler call seems so pointless :(

How about reading next time m'kay?

Quote:

---

The type qualifier

---

__restrict isn't a type, its a type qualifier just like const

It doesn't mean you can't change the object, its just a way of telling the compiler that it should be the only thing pointing to that object. But of course theres an exception

Quote:

---

The phrase "at the moment" means
that in some circumstances within a function or block aliases can be created from the orig-
inal restrict-qualified pointer as long as those aliases are elminated by the end of the func-
tion or block.

---

I know full well what you're talking about, and I already answered you. Howver, don't just take my word for it... Ta-dah! As stated, restrict aka __restrict doesn't have anything to do with making a pointer unmodifyable. That would be const. :rolleyes:


Quzah.

Quote:

---

Originally Posted by quzah

__restrict doesn't have anything to do with making a pointer unmodifyable. That would be const. :rolleyes:

---

Alright Quzah I may have misunderstood you. Ok I know what const does, I probably didn't mean what I said, I hope.

Ok so what I meant is that __restrict says that a different pointer cannot access the contents of the __restrict/restricted pointer.

The gcc documentation does not make any sense, because it doesn't give any good examples. I'm an example kind of guy. The docs doesn't seem to explain correctly for me because I cannot express what they're saying in a good example to show myself what __restrict/restrict really does.

Could somebody give me an example of using __restrict?

http://groups-beta.google.com/group/...be7487549e32db

EXCELLENT link Dave, thank you =]