const and volatile

[Dale Worley]

In article <1991May17.213923.17879 at ready.eng.ready.com> dhoward at ready.eng.ready.com (David Howard) writes:
   I declare:

   const unsigned char *device = (unsigned char *)0x600000b;

   Then I do:

   *device = 0x01;

   The compiler complains:

   'attempt to modify a const'

   what I want is for the pointer to be const, but not what it points to!

Say: "unsigned char * const device = ...;"  Obvious, isn't it?  :-)

   If I declare the pointer:

   volatile unsigned char *device = 0x600000e;

   the compiler treats BOTH the pointer and pointee as volatile. By that
   I mean, when I use the pointer, the compiler always reloads the pointer
   itself, and also always reaccesses the dereferenced location. In this
   case it works OK, but generates extra code to reload the pointer with
   0x600000e every time I use it.

The compiler is conforming, but it is wasting effort.  Hope that the
next version of the compiler is more efficient.

Dale Worley		Compass, Inc.			worley at compass.com
--
Conspiracy is the opiate of the asses.