http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55671
--- Comment #5 from loose at astron dot nl 2012-12-13 11:09:43 UTC ---
If this is by design, then the documentation is buggy. Here's a literal quote
form the man page of g++
-Wconversion
Warn for implicit conversions that may alter a value. This includes
conversions between real and integer, like "abs (x)" when "x" is
"double"; conversions between signed and unsigned, like "unsigned
ui = -1"; and conversions to smaller types, like "sqrtf (M_PI)". Do
not warn for explicit casts like "abs ((int) x)" and "ui =
(unsigned) -1", or if the value is not changed by the conversion
like in "abs (2.0)". Warnings about conversions between signed and
unsigned integers can be disabled by using -Wno-sign-conversion.
For C++, also warn for confusing overload resolution for user-
defined conversions; and conversions that will never use a type
conversion operator: conversions to "void", the same type, a base
class or a reference to them. Warnings about conversions between
signed and unsigned integers are disabled by default in C++ unless
-Wsign-conversion is explicitly enabled.
It explicitly gives the example "unsigned ui = -1" as an example.
Furthermore, older g++ compilers used to give this warning. I tried it with g++
4.1.2 and it properly gives a warning.
I also find it a bit counter-intuitive that gcc *does* warn about it, whereas
g++ does *not*.
