GCC 3.4.0: a derived class can't access the data member of a template base class

GCC 3.4.0: a derived class can't access the data member of a template base class

[Frank Chow]

Windows 2000 sp4
gcc (GCC) 3.4.0 (mingw special)

The following code can not be compiled by gcc (GCC) 3.4.0 (mingw special)

// try.cpp
#include <iostream>

struct B
{
	size_t nSize;
};

template <typename T>
struct D : public T
{
	D()
	{
		nSize = sizeof(T);
	}
};

using namespace std;

int main()
{
	D<B> sth;
	cout << sth.nSize << endl;
	
	return 0;
}

 (compile instruction)
H:\current2>g++ -o try try.cpp
 (output)
try.cpp: In constructor `D<T>::D()':
try.cpp:13: error: `nSize' undeclared (first use this function)
try.cpp:13: error: (Each undeclared identifier is reported only once for each fu
nction it appears in.)

By the way, gcc (GCC) 3.3.1 (cygwin version) can compile this code successfully, so do Visual C++ .Net (cl v 13.10.3077).

Re: GCC 3.4.0: a derived class can't access the data member of a template base class

[Alexandre Oliva]

> template <typename T> struct D : public T { D() { nSize = sizeof(T);
> } };


nSize is not a template-dependent name, so it's bound at parse time,
rather than at template instantiation time.  You must use this->nSize
or T::nSize to make it template-dependent.

> By the way, gcc (GCC) 3.3.1 (cygwin version) can compile this code
> successfully

That was a bug, fixed in 3.4.

> so do Visual C++ .Net (cl v 13.10.3077).

You'll have to report this bug to someone else, then :-)

-- 
Alexandre Oliva             http://www.ic.unicamp.br/~oliva/
Red Hat Compiler Engineer   aoliva@{redhat.com, gcc.gnu.org}
Free Software Evangelist  oliva@{lsd.ic.unicamp.br, gnu.org}