operator=() is private in ios_base. Using private inheritance of
ios_base the program below fails in the constructor when '=' is used
(but not during memory initialization). I don't understand why
assignment is prohibited.
art
Program 1 fails
# include <ostream>
using namespace std;
class thing : private ios_base {
ostream& xo;
public:
thing(ostream& y) : xo(y) { xo = y; }
};
gcc.3.4.4 messaging
x.cpp: In member function `std::basic_ios<char, std::char_traits<char> >& std::basic_ios<char,
std::char_traits<char> >::operator=(const std::basic_ios<char, std::char_traits<char> >&)':
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ios_base.h:784: error:
`std::ios_base& std::ios_base::operator=(const std::ios_base&)' is private
x.cpp:9: error: within this context
std::ios_base was never meant to be copy-able/assign-able, this has
nothing to do with public/private *inheritance*, since it is the members
of the base that are private, and thus inaccessible to any derived
classes.
In your thing::thing ctor:
"xo(y)" initializes the member *reference* (essentially taking the address
of y), whereas "xo = y;" is assigning the *object* referenced by 'ox',
which is not the same. This is why you hit the inaccessible assignment
error.
HTH,
Fang
David Fang
http://www.csl.cornell.edu/~fang/
http://www.achronix.com/