Re: Guarantee of side-effect free assignment
Alf P. Steinbach ha scritto:
From discussions in [comp.lang.c++] and [comp.lang.c++.moderated], as
well as articles on the net about concurrency in C++, I'm reasonably
sure that given
#include <iostream>
#include <ostream>
struct S { S(){ throw 123; } int foo(){ return 666; } };
int main()
{
S* p = 0;
try
{
p = new S();
}
catch( ... )
{}
if( p ) { std::cout << p->foo() << std::endl; }
}
there is no guarantee that this code will not end up in a call to
p->foo() with an invalid pointer p, i.e., that might well happen.
The the latest draft N2369 effectively replaced the controversial
concept of "sequence points" with the new concept of "sequenced before"
(see 1.9/14 for details). Paragraph 5.17/1 has therefore been rewritten
and, if I interpret it correctly, it rules out this possibility: (with
emphasis added)
"In all cases, the assignment is *sequenced after* the value computation
of the right and left operands, and before the value computation of the
assignment expression."
As the assignment is sequenced after the the computation of the right
operand, it should not occur when such computation terminates
prematurely because of a exception.
Surely that couldn't have been the committee's intention?
Why isn't assignment treated as a function call?
With the new wording of 5.17/1, I don't see any need for that.
Just my opinion,
Ganesh
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