https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98947
Bug ID: 98947
Summary: Incorrect warning when using a ternary operator to
select one of two volatile variables to write to
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: headch at gmail dot com
Target Milestone: ---
Using a ternary operator to select one of two variables of the same
volatile-qualified type and then writing into the selected variable yields a
warning in C++2a mode, which I believe either it should not or it is
incorrectly worded.
$ cat test.cpp
volatile int x, y;
void f(bool b) {
(b ? x : y) = 27;
}
$ g++-10.2.0 -Wall -Wextra -std=c++2a -c test.cpp
test.cpp: In function ‘void f(bool)’:
test.cpp:4:14: warning: using value of simple assignment with
‘volatile’-qualified left operand is deprecated [-Wvolatile]
4 | (b ? x : y) = 27;
| ~~~~~~~~~~~~^~~~
test.cpp:4:14: warning: using value of simple assignment with
‘volatile’-qualified left operand is deprecated [-Wvolatile]
$ g++-10.2.0 --version
g++-10.2.0 (Gentoo 10.2.0-r5 p6) 10.2.0
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
I’m not sure whether this code is even deprecated or not. Either way, though,
the warning is wrong. I am not, as the warning claims, using the return value
of the assignment operator.
The roughly equivalent form “*(b ? &x : &y) = 27;” does not generate a warning.
The even more similar, and silly, “*&(b ? x : y) = 27;” also does not generate
a warning.
