help: derived class uses base class protect value

[tomy]

Hi Group:
I just come to a confusion thing which is different from what my text
book says.
The code is below:

//************************************
class Base
{
protected:
int mutex;
};

class Foo : public Base
{
public:
inline void bar(int v) { mutex = v;}
};
//***************************************
compiled result is:

foo.h: In function `void bar()':
foo.h:33: error: `mutex' undeclared (first use this function)
foo.h:33: error: (Each undeclared identifier is reported only once for
each function it appears in.)
//***************************************
To my surprise, the code won't be compiled. The compiler(gcc) says the
variable mutex didn't be declared. However the text book told me the
derived class could see the Base class' protected thing through public
derived, didn't it?

could someone give me any suggestion?


--tomy

 

[Daniel T.]

Hi Group:
I just come to a confusion thing which is different from what my text
book says.
The code is below:

//************************************
class Base
{
protected:
int mutex;
};

class Foo : public Base
{
public:
inline void bar(int v) { mutex = v;}
};
//***************************************
compiled result is:

foo.h: In function `void bar()':
foo.h:33: error: `mutex' undeclared (first use this function)
foo.h:33: error: (Each undeclared identifier is reported only once for
each function it appears in.)
//***************************************
To my surprise, the code won't be compiled. The compiler(gcc) says the
variable mutex didn't be declared. However the text book told me the
derived class could see the Base class' protected thing through public
derived, didn't it?

could someone give me any suggestion?

I pasted the code above into my gcc complier and it compiled just fine.
Are you sure that the code above is what you have?

 

[tomy]

I pasted the code above into my gcc complier and it compiled just fine.
Are you sure that the code above is what you have?

Thanks for your post.
Sorry, I tried again the code above which actually do work.

The original code is with template. And as below :

//******************************************************
template<class T>
class Base
{
protected:
int mutex;
};

template<class T>
class Foo : public Base<T>
{
public:
inline void bar(int v) { mutex = v;}
};

//****************test main***********
int main()
{
Foo<int> foo;
foo.bar(100);
return 0;
}
//****************************************************
compiled result:

foo.cpp: In member function `void Foo<T>::bar(int)':
foo.cpp:13: error: `mutex' undeclared (first use this function)
foo.cpp:13: error: (Each undeclared identifier is reported only once
for each function it appears in.)
//*****************************************************

I wonder what happens with the TEMPLATE?

--tomy

 

[Kai-Uwe Bux]

Thanks for your post.
Sorry, I tried again the code above which actually do work.

The original code is with template. And as below :

//******************************************************
template<class T>
class Base
{
protected:
int mutex;
};

template<class T>
class Foo : public Base<T>
{
public:
inline void bar(int v) { mutex = v;}

Try

inline void bar(int v) { this->mutex = v;}

or

inline void bar(int v) { Base<T>::mutex = v;}

BTW: the inline is redundant.

};

//****************test main***********
int main()
{
Foo<int> foo;
foo.bar(100);
return 0;
}
//****************************************************
compiled result:

foo.cpp: In member function `void Foo<T>::bar(int)':
foo.cpp:13: error: `mutex' undeclared (first use this function)
foo.cpp:13: error: (Each undeclared identifier is reported only once
for each function it appears in.)
//*****************************************************

I wonder what happens with the TEMPLATE?

Templates is where some strange name-lookup issues kick in.


Best

Kai-Uwe Bux

 

[tomy]

Great, your proposal really do good job. Both of them work fine.
--"Templates is where some strange name-lookup issues kick in" That's
the key.

Many Thanks.

--tomy

 

[Marcus Kwok]

Great, your proposal really do good job. Both of them work fine.
--"Templates is where some strange name-lookup issues kick in" That's
the key.

Tomy,
Please don't top-post. Your replies belong below or interleaved with
the original quoted message, with irrelevant context snipped.

Anyway, for a little more info, look in the FAQ:
http://www.parashift.com/c++-faq-lite/templates.html#faq-35.18