Template type usage from base classes

Template type usage from base classes

[Michael Kaes]

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Hi,

I am having some problems with a template structure I am using and was
hoping that someone around here could give me a hint. The code I am
using works fine on the Visual Studio 8 compiler from MS but it does
not compile on the gcc.
I stripped it down as good as I could and it looks valid to me but
still it only compiles with VS8 and not with the GCC. The interesting
thing is that it does work when I only use one template parameter.
I am using gcc version 4.2.4 (Debian 4.2.4-3). Could this be a bug in
the gcc or is this simply not valid c++ code and the VS8 is only
generous?

The stripped down example:
#include<iostream>

template<
	size_t sizeValue,
	typename NumericType>
class Base
{
	protected:
		NumericType n;
	public:
		typedef NumericType val_t;

		Base(val_t t):n(t)
		{
		}
};


template<
	size_t sizeValue,
	typename unusedType
>
class Derived;


template<
	size_t sizeValue
>
class Derived<sizeValue, int> : public Base<sizeValue, int>
{
	public:
		Derived() : Base<sizeValue, val_t>(1)
		{
		}
};

int main()
{
	Derived<12, int> d;
}



The error message I get is the following

templateTest.cpp: In constructor Derived<sizeValue, int>::Derived():
templateTest.cpp:32: error: val_t was not declared in this scope
templateTest.cpp:32: error: template argument 2 is invalid
templateTest.cpp: In constructor Derived<sizeValue, int>::Derived()
[with unsigned int sizeValue = 12u]:
templateTest.cpp:39:   instantiated from here
templateTest.cpp:32: error: no matching function for call to Base<12u,
int>::Base()
templateTest.cpp:13: note: candidates are: Base<sizeValue,
NumericType>::Base(NumericType) [with unsigned int sizeValue = 12u,
NumericType = int]
templateTest.cpp:7: note:                 Base<12u, int>::Base(const
Base<12u, int>&)


Thanks in advance

Michael Kaes

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#include<iostream>

template<
	size_t sizeValue,
	typename NumericType>
class Base
{
	protected:
		NumericType n;
	public:
		typedef NumericType val_t;

		Base(val_t t):n(t)
		{
		}
};


template<
	size_t sizeValue,
	typename unusedType
>
class Derived;


template<
	size_t sizeValue
>
class Derived<sizeValue, int> : public Base<sizeValue, int>
{
	public:
		Derived() : Base<sizeValue, val_t>(1)
		{
		}
};

int main()
{
	Derived<12, int> d;
}

Re: Template type usage from base classes

[Gian Lorenzo Meocci]

Try to add

typedef typename Base<sizeValue, int>::val_t val_t;
after
                Derived() : Base<sizeValue, val_t>(1)
                {
                }

-- 
Gian Lorenzo Meocci
http://www.meocci.it

Re: Template type usage from base classes

[Eljay Love-Jensen]

Hi Michael,

Try this...

template<
  size_t sizeValue
  >
class Derived<sizeValue, int> : public Base<sizeValue, int>
{
public:
  Derived() : Base<sizeValue, typename Base<sizeValue, int>::val_t>(1)
  {
  }
};

Microsoft's compiler is in error, it should not accept your non-compliant
code.

HTH,
--Eljay

Re: Template type usage from base classes

[Michael Kaes]

Thanks everybody,

works as it I expected it :-)
Took me nearly a day. I should stick more to gcc than to VS8.


Regards

Michael Kaes

Re: Template type usage from base classes

[Tom Browder]

On Tue, Aug 19, 2008 at 11:44 AM, Michael Kaes <michael.kaes@gmail.com> wrote:
> Thanks everybody,
>
> works as it I expected it :-)
> Took me nearly a day. I should stick more to gcc than to VS8.

I've had similar experiences with a cross-platform project where my
coworker is doing the Windows part and I'm doing the Linux part.

I get gcc-4.3.1 warnings and errors that he doesn't get *until* he
uses the /Za argument to his MSVC++ 2005 compiler.

-Tom