[lkml]   [1997]   [Sep]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: Style question: comparison between signed and unsigned? (Matthias Urlichs):

    >> /* check that we got a valid packet */
    >> if (i < sizeof(struct pkthdr))
    >> return SHORT_PACKET;

    >> [...] gcc will [...] warn [...] because "i" is signed, but "sizeof"
    >> is unsigned.

    > And because GCC knows how to figure out the size of the struct, but then
    > forgets to check if the high bit of that size is set (otherwise you cannot
    > run into a problem in the first place). ^^^^^^

    Yes, you could run into problems. sizeof(...) has unsigned type
    size_t, while i is a signed int. Thus the comparison
    (i < sizeof(struct pkthdr))
    is equivalent to
    ((size_t) i < sizeof(struct pkthdr)),
    unless there was some clandestine change of the C standard. Here, the
    problem is not that sizeof(...) is converted to signed int, but
    that i is converted to an unsigned type. This could lead to undesired
    consequences if we hadn't already handled the case i < 0.

    > In other words, that warning _is_ a compiler bug.

    No, it isn't. (If the compiler had decided _not_ to warn about that
    implicit conversion because "the user knows what he's doing", _that_
    clearly would have been a bug in your case :-)

    Bodo M"oller

     \ /
      Last update: 2005-03-22 13:40    [W:0.018 / U:30.300 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site