[Bug c/39170] cannot silence -Wconversion warnings for bit-fields

[manu at gcc dot gnu dot org]

------- Comment #3 from manu at gcc dot gnu dot org  2009-03-08 03:30 -------
> The old behavior was just fine!

You absolutely did not understand what the old -Wconversion did. 

http://gcc.gnu.org/wiki/NewWconversion

But if you still want the old behaviour, just use -Wtraditional-conversion.

> I'm sure many people do not even realize they are NOT getting implicit
> conversions warnings anymore because they are not caught by "-Wall"

See the FAQ in the link above.

> anymore. We only discovered this be tracing a bug in our code! We then

The new Wconversion is mentioned in the changes of GCC 4.3.

> turned on "-Wconversion" only to discover thousands of warnings with no
> way practical way to fix them. 

I admit it is unfortunate that there is no way to specify casts to bit-fields.
But that is hardly the fault of Wconversion. Nonetheless, it could be possible
to use bitwise-and to tell Wconversion that some conversion is really desired.
Example:

struct foo
{
    int a : 2;
};

void assign( struct foo v, int x )
{
    v.a = x & 0x3;
}

Do you think this would be an acceptable solution? (I don't know if this works
now in GCC 4.4)


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu dot org
             Status|UNCONFIRMED                 |WAITING
            Summary|-Wconversion useless        |cannot silence -Wconversion
                   |                            |warnings for bit-fields


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39170