On Tue, Jun 17, 2008 at 08:51:24PM -0700, Karen Shaeffer wrote: > I see your point. My sticking point is that the process is actually > running on a physical machine.
And that's the problem. You, like many C programmers, have in your head a physical machine model where pointer variables are physical machine addresses and other variables are physical memory locations. But C doesn't necessarily work that way (except at -O0); if it did, programs would run substantially slower. The compiler can make optimizations (like reusing values in registers) in certain circumstances. Anywhere in the standard where you see that a behavior is undefined, read that as meaning, the compiler is allowed to produce an arbitrary code sequence, so it will produce the fastest, or smallest, or simplest-to-implement sequence. > And the addresses, although virtual, > do translate to a unique physical memory location. And, the value > stored in that location cannot be 0 and 5 at the same time. Right, but since it's const, the compiler is allowed to assume that it is, well, const! That means that if it has already read the value into a register, it can assume that the register is still valid for the remainder of the program execution, even if you decide to violate the rules of C and change the "constant". That's why it appears to be 0 and 5 at the same time. To get rid of that behavior, you'd have to force the compiler to read every variable from memory every time, and not use registers at all.
