https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105283
Bug ID: 105283
Summary: Ternary operator and precedence warning
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: dcb314 at hotmail dot com
Target Milestone: ---
For this C++ code:
extern int g( int);
void f( int a, int b)
{
if (a & 0x03 == 3)
g( 1);
if (a + (b > 10) ? g( 1) : g( 2))
g( 10);
}
gcc finds the first problem, but not the second:
$ /home/dcb/gcc/results/bin/gcc -c -g -O2 -Wall -Wextra -Wparentheses
-Wint-in-bool-context apr15b.cc
apr15b.cc: In function ‘void f(int, int)’:
apr15b.cc:6:22: warning: suggest parentheses around comparison in operand of
‘&’ [-Wparentheses]
6 | if (a & 0x03 == 3)
| ~~~~~^~~~
$
Here is recent clang on the same code:
$ /home/dcb/llvm/results/bin/clang -c -Wall apr15b.cc
apr15b.cc:6:8: warning: & has lower precedence than ==; == will be evaluated
first [-Wparentheses]
if (a & 0x03 == 3)
^~~~~~~~~~~
apr15b.cc:6:8: note: place parentheses around the '==' expression to silence
this warning
if (a & 0x03 == 3)
^
( )
apr15b.cc:6:8: note: place parentheses around the & expression to evaluate it
first
if (a & 0x03 == 3)
^
( )
apr15b.cc:9:19: warning: operator '?:' has lower precedence than '+'; '+' will
be evaluated first [-Wparentheses]
if (a + (b > 10) ? g( 1) : g( 2))
~~~~~~~~~~~~ ^
apr15b.cc:9:19: note: place parentheses around the '+' expression to silence
this warning
if (a + (b > 10) ? g( 1) : g( 2))
^
( )
apr15b.cc:9:19: note: place parentheses around the '?:' expression to evaluate
it first
if (a + (b > 10) ? g( 1) : g( 2))
^
( )
2 warnings generated.
$
Please note I only had to use -Wall on clang to get the second warning
and the warning message itself is IMHO more descriptive.
