Templates + Inheritance problem

Ling-hua Tseng uranus@it.muds.net
Thu Jul 19 15:42:00 GMT 2007


It's not a bug.
When you are using class template, the `total template specialization' may 
be wrote by someone.
Since the C++ compiler expect anything, you should to use one of the 
following 3 solutions:
  1. use `this->Baz()' instead of `Baz()'.
  2. write `using Foo<KEY>::Baz();' in the derived class template.
  3. use `Foo<KEY>::Baz()' instead of `Baz()'.

It's described in item 43 of this book `Effective C++ 3/e'.
(Its title is "Know how to access names in templatized base classes".)

On Thu, 19 Jul 2007 10:26:25 -0500, John Gateley wrote
> Hi, I've found strange behavior, possibly a bug, but more likely a
> problem with my understanding. Here's the code:
> 
> template<class KEY> class Foo {
> public:
> 	void Baz() {}
> };
> template<class KEY> class Bar : public Foo<KEY> {
> public:
> 	void Bum() { Baz(); }
> };
> 
> (I know it doesn't make much sense, I reduced the problem
> down to simplest terms). I get an error compiling:
> 
> gateley@gateley:~/tmp$ g++ -c Foo.C 
> Foo.C: In member function 'void Bar<KEY>::Bum()':
> Foo.C:11: error: there are no arguments to 'Baz' that depend on a 
> template parameter, so a declaration of 'Baz' must be available 
> Foo.C:11: error: (if you use '-fpermissive', G++ will accept your 
> code, but allowing the use of an undeclared name is deprecated)
> 
> Can someone tell me why Baz is undeclared here?
> 
> version:
> gateley@gateley:~/tmp$ g++ -v
> Using built-in specs.
> Target: i486-linux-gnu
> Configured with: ../src/configure -v --enable-languages=c,c++,
> fortran,objc,obj-c++,treelang --prefix=/usr --enable-shared --with-
> system-zlib --libexecdir=/usr/lib --without-included-gettext --
> enable-threads=posix --enable-nls --program-suffix=-4.1 --enable-
> __cxa_atexit --enable-clocale=gnu --enable-libstdcxx-debug --enable-
> mpfr --enable-checking=release i486-linux-gnu Thread model: posix 
> gcc version 4.1.2 20060928 (prerelease) (Ubuntu 4.1.1-13ubuntu5)
> 
> Thanks,
> 
> j
> 
> -- 
> John Gateley <gateley@jriver.com>



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