Fix the conversion to void*

LLVM libc++ does not implement std::basic_ios::operator void*, even in
C++03.

Author: lrineau

Inventor/include/CGAL/IO/Inventor_ostream.h

@@ -53,9 +53,10 @@ class Inventor_ostream_base {
         || defined BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS
     typedef const void* Const_void_ptr;
     operator Const_void_ptr () const {
-        if ( m_os)
-            return *m_os;
+      if ( m_os->fail() )
         return 0;
+      else
+        return static_cast<Const_void_ptr>(m_os);
     }
     #else
     explicit operator bool ()

Inventor/include/CGAL/IO/VRML_2_ostream.h

@@ -47,13 +47,13 @@ class VRML_2_ostream {
         || defined BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS
     typedef const void* Const_void_ptr;
     operator Const_void_ptr () const {
-        if ( m_os)
-            return *m_os;
+      if ( m_os->fail() )
         return 0;
+      else
+        return static_cast<Const_void_ptr>(m_os);
     }
     #else
-    explicit operator bool ()
-    {
+    explicit operator bool () {
       return m_os && !m_os->fail();
     }
     #endif

Polyhedron_IO/examples/Polyhedron_IO/off2iv.cpp

@@ -81,6 +81,7 @@ int main( int argc, char **argv) {
     CGAL::Inventor_ostream os( *p_out);
     CGAL::File_writer_inventor  writer;
     CGAL::generic_copy_OFF( *p_in, *p_out, writer);
+    if(!os) return EXIT_FAILURE;
     os.close();
     vout << "    .... done." << endl;
 

Polyhedron_IO/examples/Polyhedron_IO/off2vrml.cpp

@@ -87,11 +87,13 @@ int main( int argc, char **argv) {
         CGAL::VRML_1_ostream os( *p_out);
         CGAL::File_writer_inventor  writer;
         CGAL::generic_copy_OFF( *p_in, *p_out, writer);
+        if(!os) return EXIT_FAILURE;
         os.close();
     } else {
         CGAL::VRML_2_ostream os( *p_out);
         CGAL::File_writer_VRML_2  writer;
         CGAL::generic_copy_OFF( *p_in, *p_out, writer);
+        if(!os) return EXIT_FAILURE;
         os.close();
     }
     vout << "    .... done." << endl;