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