[Bug c++/42330] New: undefined reference to "static const int" in class when passing as "const int &" to a function

[aijunbai at gmail dot com]

consider the flowing code:

struct A {
static const int i = 0;
};

void foo(int)
{
}

void bar(const int &)
{
}

int main() {
foo(A::i);
bar(A::i);

return 0;
}

when compiling with -O0 option, g++ reports that: undefined reference to
`A::i',
but it will be ok if i use -O3 option.

gcc -v says:
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.1-4ubuntu8'
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--enable-multiarch --enable-linker-build-id --with-system-zlib
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
--enable-targets=all --disable-werror --with-arch-32=i486 --with-tune=generic
--enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu
--target=i486-linux-gnu
Thread model: posix
gcc version 4.4.1 (Ubuntu 4.4.1-4ubuntu8)


-- 
   Summary: undefined reference to "static const int" in class when
passing as "const int &" to a function
   Product: gcc
   Version: 4.4.1
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
    ReportedBy: aijunbai at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42330

[Bug c++/42330] undefined reference to "static const int" in class when passing as "const int &" to a function

[aijunbai at gmail dot com]

--- Comment #2 from aijunbai at gmail dot com  2009-12-08 09:46 ---
(In reply to comment #1)
> You aren't defining anywhere A::i, just add, after struct A:
> 
>   const int A::i;
> 
> and things will be fine.
> 
> *** This bug has been marked as a duplicate of 42101 ***
> 

thanks for your reply.

i found that no errors will be reported if i delete the line `bar(A::i)', so is
that a bug?

in fact the original code is like:
template 
class A
{
static const int i = -1;
}

template <>
class A<0>
{
static const int i = 0;
}

//and some other specializations...

and i don't want to write lots of "const int A::i"...


-- 

aijunbai at gmail dot com changed:

   What|Removed |Added

 Status|RESOLVED|UNCONFIRMED
 Resolution|DUPLICATE   |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42330

[Bug c++/42330] undefined reference to "static const int" in class when passing as "const int &" to a function

[aijunbai at gmail dot com]

--- Comment #5 from aijunbai at gmail dot com  2009-12-08 11:52 ---
(In reply to comment #4)
> (In reply to comment #3)
> > (In reply to comment #2)
> > > and i don't want to write lots of "const int A::i"...
> > 
> > You have to, your code is not valid if you use A::i in the program but it 
> > has
> > no definition.  This is not a compiler bug.
> 
> Actually you don't have to write lots, just one:
> 
> template const A::i;
> 

I tried so, but it seems do not work, could you please explain more detailedly?
thx~


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42330

[Bug c++/42330] undefined reference to "static const int" in class when passing as "const int &" to a function

[aijunbai at gmail dot com]

--- Comment #7 from aijunbai at gmail dot com  2009-12-08 13:02 ---
(In reply to comment #6)
> (In reply to comment #5)
> > > 
> > > template const A::i;
> > > 
> > 
> > I tried so, but it seems do not work, could you please explain more 
> > detailedly?
> > thx~
> 
> I missed the "int" out:
> 
> template const int A::i;
> 

thanks for your help, but it still can not be compiled under gcc 4.4.1


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42330

[Bug c++/42330] undefined reference to "static const int" in class when passing as "const int &" to a function

[aijunbai at gmail dot com]

--- Comment #9 from aijunbai at gmail dot com  2009-12-08 14:06 ---
(In reply to comment #8)
> Then show here exactly what you are trying to compile. Note: this is *not*
> gcc-help.
> 

alright, take the flowing code as an example:

template
struct A {
static const int i = -1;
};

template<>
struct A<0> {
static const int i = 0;
};

template<>
struct A<1> {
static const int i = 1;
};

template  const int A::i;

int foo(int)
{
}

int bar(const int &)
{
}

int main()
{
foo(A<1>::i); //ok here
bar(A<0>::i); //g++ complains undefined reference to `A<0>::i'

return 0;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42330