> On a related but separate note, is there any standard that guarantees > that casting -1 to a function pointer type is reasonably portable?
This idiom is used widely enough to overload an argument so that it can contain either a valid pointer, or convey a non-pointer state. Take /usr/include/pthread.h, for example. It's not a function pointer, but it's in the same ballpark: GNU LIBC: #define PTHREAD_CANCELED ((void *)-1) Solaris: #define PTHREAD_CANCELED (void *)-19 FreeBSD: #define PTHREAD_CANCELED ((void *) 1) NetBSD: /* * POSIX 1003.1-2001, section 2.5.9.3: "The symbolic constant * PTHREAD_CANCELED expands to a constant expression of type (void *) * whose value matches no pointer to an object in memory nor the value * NULL." */ #define PTHREAD_CANCELED ((void *) 1) The UNIX call sigaction() does actually use such "invalid" casted function pointers: http://www.opengroup.org/onlinepubs/7990989775/xsh/sigaction.html Where the function pointer sa_handler member of the struct sigaction can contain SIG_IGN and SIG_ERR. On one popular version of UNIX they are defined as: #define SIG_IGN (void(*)(int))1 #define SIG_ERR (void(*)(int))-1 ____________________________________________________________________________________ Do you Yahoo!? Everyone is raving about the all-new Yahoo! Mail beta. http://new.mail.yahoo.com ----------------------------------------------------------------------------- To unsubscribe, send email to [EMAIL PROTECTED] -----------------------------------------------------------------------------
