Re: Accessing a protected member in a derived class

From:
Victor Bazarov <v.bazarov@comcast.invalid>
Newsgroups:
comp.lang.c++
Date:
Sat, 23 Jul 2011 08:38:51 -0400
Message-ID:
<j0efd0$81i$1@dont-email.me>
On 7/23/2011 7:39 AM, Johannes Schaub wrote:

Tom wrote:

Hi NG,

The following example does not compile using g++. The compiler says
"error: ???iMyVal??? was not declared in this scope" in Method MyFunction
of the derived class:

template<typename T>
class MyBase
{
protected:
   int iMyVal;
};

template<typename T>
class MyDerived : public MyBase<T>
{
   void MyFunction()
   {
     // this->iMyVal = 10;
     iMyVal = 10;
   }
};

int main()
{
   MyDerived<int> derived;
   return 0;
}

Using the line with the this-> works fine. After removing the template
stuff the code compiles also fine without this->:


"iMyVal" is an unqualified names. Unqualified name lookup won't look into
base classes whose type depends on template parameters (such as "T", or
"MyBase<T>").

If you say "this->iMyVal" or "MyDerived::iMyVal", you are using class member
access and qualified name lookup respectively. Those don't ignore dependent
base classes, and will thus find "int iMyVal;" when instantiating
"MyDerived<int>::MyFunction".


To the OP:
  http://www.parashift.com/c++-faq-lite/templates.html#faq-35.19

To Johannes:
  http://www.parashift.com/c++-faq-lite/how-to-post.html#faq-5.5

V
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