g++ may fail to compile __packed structures
Craig Rodrigues
rodrigc at crodrigues.org
Tue Sep 7 05:25:42 PDT 2004
On Mon, Sep 06, 2004 at 01:24:15PM -0700, Pavlin Radoslavov wrote:
> It appears that the lastest g++ compiler that comes with FreeBSD may
> fail to compile a __packed structure when one of its fields is
> passed by reference. At the end of this email is a sample program
> that demonstrates the problem. The compilation error is:
>
> pavlin at carp[14] g++34 test.cc
> test.cc: In function `int main()':
> test.cc:22: error: cannot bind packed field `f1.foo::f' to `int&'
> Exit 1
>
> The problem appears to exist only with the recent g++ compiler that
> comes with FreeBSD:
This change was made recently to gcc:
http://gcc.gnu.org/ml/gcc-patches/2003-07/msg01664.html
Apparently in C++, you are not allowed to have non-const references
to packed fields. See:
http://www.comnets.rwth-aachen.de/doc/c++std/decl.html#dcl.init.ref
Your testcase will compile if you change your copy_out function to:
void
copy_out(const int& i)
{
// i = 0x11223344;
}
but your testcase will not be too useful.
You might want to follow up on one of the GCC mailing lists.
--
Craig Rodrigues
http://crodrigues.org
rodrigc at crodrigues.org
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