g++-4.3.0 -ansi -pedantic-errors -std=c++0x -Wall -Wconversion
issues the following diagnostic on the following code:
// test case:
typedef unsigned short ushort;
enum {
FOO = 0x13
};
template <typename T>
inline
void
andnot(T& lv, T&& rv) {
lv &= ~rv;
}
template <typename T>
inline
void
andnot(T& lv, const T& rv) {
lv &= ~rv;
}
int
main(int, char*[]) {
ushort x = 99;
x = ~FOO;
x &= ~FOO; // -Wconversion
x = x & ~FOO; // -Wconversion
x = x & ushort(~FOO); // -Wconversion
x = x & ushort(~ushort(FOO)); // -Wconversion
x &= static_cast<ushort>(~FOO); // -Wconversion
x &= ~x;
// andnot(x, FOO); // no match
andnot(x, ushort(FOO)); // -Wconversion
return x;
}
// end test case.
../../../src/conv.cc: In function 'int main(int, char**)':
../../../src/conv.cc:25: warning: conversion to 'ushort' from 'int' may alter
its value
../../../src/conv.cc:26: warning: conversion to 'ushort' from 'int' may alter
its value
../../../src/conv.cc:27: warning: conversion to 'ushort' from 'int' may alter
its value
../../../src/conv.cc:28: warning: conversion to 'ushort' from 'int' may alter
its value
../../../src/conv.cc:29: warning: conversion to 'ushort' from 'int' may alter
its value
../../../src/conv.cc: In function 'void andnot(T&, T&&) [with T = ushort]':
../../../src/conv.cc:32: instantiated from here
../../../src/conv.cc:11: warning: conversion to 'short unsigned int' from 'int'
may alter its value
All warnings disappear if -Wconversion is omitted.
I don't understand the rationale why some of the above lines are diagnostic
free (assignments), and others trigger the diagnostic, so I cannot claim which
are valid w.r.t. -Wconversion. I did however expect a function-style
(ctor-style) cast or static_cast to suppress the diagnostic.
Is there a bug, or proper "workaround" to locally suppress the diagnostic?
keywords: diagnostic
--
Summary: -Wconversion rejects bitwise negation and assignment,
cannot cast around
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: fang at csl dot cornell dot edu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35852
