Ambiguity in semantics of assignments?

[Dave Vandervies]

There is really nothing to discuss.

int i = 3;
i = i + 1;

is valid. There is no real difference between the above
and code posted by the OP.

Chapter and verse?

(You could cheat and just point to my post replying to Arthur's request
for chapter and verse. But, based on the discussion we've seen, it's
obviously not immediately and universally clear that this is the case.)


dave

 

[Chris Torek]

What I am unsure about is what the following means:

"The order of evaluation of the operands is unspecified.
If an attempt is made to modify the result of an assignment
operator or to access it after the next sequence point,
the behavior is undefined."

Which is 6.5.16#4

How can you modify the result of an assignment operator?

I believe this refers to tricks like this:

struct S { int a[10]; };

struct S s1, s2;
int *p;

p = (s1 = s2).a;
p[2] = 42; /* presumably, this violates 6.5.16#4 */

This "accesses it after a sequence point" *and* modifies it; to
just modify it, all in one swell foop as it were, we might write:

(s1 = s2).a[2] = 42;

eliminating the variable "p" entirely.