#include <iostream>
#include <list>

template<class mt_policy>
class Base
{
public:
int a;
};

template<class mt_policy = int>
class signal0 : public Base<mt_policy>
{
public:
void aaa()
{
std::cout<<"a = "<<a<<std::endl;
}
};

int main()
{
signal0<int> p;
p.aaa();
}
~

test.cpp: In member function ‘void signal0<mt_policy>::aaa()’:
test.cpp:17: error: ‘a’ was not declared in this scope

On Jul 1, 9:05 am, steve yee <yiton...@gmail.com> wrote:
> #include <iostream>
> #include <list>
>
> template<class mt_policy>
> class Base
> {
> public:
> int a;
>
> };
>
> template<class mt_policy = int>
> class signal0 : public Base<mt_policy>
> {
> public:
> void aaa()
> {
> std::cout<<"a = "<<a<<std::endl;

This is the definition of class template signal0, not an instantiation
of it. So the compiler cannot know whether any Base<mt_policy> will
provide an 'a'. For example, some specialization may not have an a.

The compiler cannot assume that a missing name will be available
through a templated base. What if there were two bases?

The solution is to fully qualify 'a': Base<mt_policy>::a

> }
>
> };
>
> int main()
> {
> signal0<int> p;
> p.aaa();}
>
> ~
>
> test.cpp: In member function ‘void signal0<mt_policy>::aaa()’:
> test.cpp:17: error: ‘a’ was not declared in this scope

Ali

steve yee wrote:
> test.cpp: In member function ‘void signal0<mt_policy>::aaa()’:
> test.cpp:17: error: ‘a’ was not declared in this scope

You have to add this to your signal0 class:

using Base<mt_policy>::a;

I don't remember now why this was standardized like that.

so this is a standard, not a bug of gcc? but vc9 can compile it.


On Jul 2, 2:00am, Juha Nieminen <nos...@thanks.invalid> wrote:
> steve yee wrote:
> > test.cpp: In member function ‘void signal0<mt_policy>::aaa()’:
> > test.cpp:17: error: ‘a’ was not declared in this scope
>
> You have to add this to your signal0 class:
>
> using Base<mt_policy>::a;
>
> I don't remember now why this was standardized like that.

steve yee wrote:
> so this is a standard, not a bug of gcc? but vc9 can compile it.

VC9 doesn't obey the standard in all respects.

steve yee wrote:
> #include<iostream>
> #include<list>
>
> template<class mt_policy>
> class Base
> {
> public:
> int a;
> };
>
> template<class mt_policy = int>
> class signal0 : public Base<mt_policy>
> {
> public:
> void aaa()
> {
> std::cout<<"a ="<<a<<std::endl;

here you need to make name 'a' dependent on template parameter
one of ways to do this, is to access 'a' through this pointer:

std::cout<<"a ="<<this->a<<std::endl;

> }
> };
>
> int main()
> {
> signal0<int> p;
> p.aaa();
> }
> ~
>
> test.cpp: In member function ‘void signal0<mt_policy>::aaa()’:
> test.cpp:17: error: ‘a’ was not declared in this scope

Juha Nieminen wrote:
> steve yee wrote:
>> so this is a standard, not a bug of gcc? but vc9 can compile it.
>
> VC9 doesn't obey the standard in all respects.

It does respect this, if you ask it too (option /Za). Default is to
compile old, pre-standard, Windows code.


Bo Persson