Hi, 

g++ 4.2.1 doesn't seem to apply hidden visibility to classes after including e.g. <ostream>. 

the following testcase was reduced: 

=== Cut ===
namespace std  __attribute__ ((__visibility__ ("default")))
{
  template < typename A > class C;
  template < typename A > int foo (C < A > *);

  template < typename A > class C
  {
  public:
    friend int foo<>(C <A > *);
  };
  extern template class C < char >;
}

struct TestClass
{
  void hidden();
};
void TestClass::hidden() {}
=== cut ===
g++ -O1 -fvisibility=hidden -fvisibility-inlines-hidden -fPIC testcase.cc -c -o nostl.o
g++ -shared -o libnostl.so nostl.o
nm -CD libnostl.so | grep TestClass 

gives

0000048c T TestClass::hidden()


the symbol is properly hidden if I put the namespace std into default visibility or otherwise try to reduce the code further.