Re: -Wconversion

[Russ Allbery <rra at stanford dot edu>]

Patrik Hagglund <patha@softlab.ericsson.se> writes:

> I still think this is confusing. -Wconversion seems to has more than one
> purpose. For example:

>      Also, warn if a negative integer constant expression is implicitly
>      converted to an unsigned type.  For example, warn about the
>      assignment `x = -1' if `x' is unsigned.  But do not warn about
>      explicit casts like `(unsigned) -1'.

> This has nothing to do with prototypes and is intreresting for
> day-to-day use.

> Isn't it better to have two different warnings? One intended for
> day-to-day use and one intended for programs with prototypes rencenlty
> added.

I'd like to second this request.  -Wconversion also caught:

    ssize_t
    function(void)
    {
        size_t n;
    
        /* ... */
    
        return n;
    }

(Admittedly with a somewhat confusing message in gcc 2.95.1 -- yeah, I
know I need to upgrade to 2.95.2.)  I found that useful; I think it's
stylistically better to write:

        return (ssize_t) n;

which -Wconversion prefers, since it makes it explicit that weird things
may happen for n > maximum positive integer that fits in ssize_t.

-- 
Russ Allbery (rra@stanford.edu)             <http://www.eyrie.org/~eagle/>