Re: mach_port

On Aug 1, 2005, at 8:01 AM, Peter Seebach wrote:

Some Apple code includes lines like:

mach_port_t masterPort = NULL;

When I compile this, I get a warning about converting a pointer to an integer
without a cast.

Yes, this is expected on gcc 4.0. Earlier versions of gcc did not flag this.

The main thing that changed is that the C standard now defines NULL as (void *) 0. Earlier versions of the language did not specify a value for NULL and most implementations defined NULL as 0.

Converting a pointer to an integer is legal but non-portable: the result is implementation-defined.

Sure enough, mach_port_t is an unsigned int. In fact, most of the things
used like this seem to be unsigned ints, which are only passed around as
cookies returned by mach calls.

So.

Why are they always initialized as though they were pointers?

You'd have to ask the authors of the code. :-) My guess is that NULL was just convenient. More strictly correct would be MACH_PORT_NULL. Tiger also introduced IO_OBJECT_NULL as ((io_object_t) 0).

Tiger was built (mostly) with gcc 3.3. As Mac OS X moves to being built with gcc 4.0, I would expect these warnings to be cleaned up.

In the I/O Kit master port case, since Jaguar there's been the constant kIOMasterPortDefault. Just pass that to any call that needs the I/O Kit master port, and you no longer need to call IOMasterPort() explicitly.

-s

--gc

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Apple Developer Technical Support Cupertino, CA 95014

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References:
	>mach_port_t (From: email@hidden (Peter Seebach))

Re: mach_port_t