template class compiling problem

[Rui Maciel]

I'm trying to write a tree class and I've just stumbled on a compiling
problem. The compiler throws an error on a piece of code which to my eyes
it is error-free. Can anyone help me with this?

Here is the error message:

<error>
/home/rui/development/C++/mytree/src/tree.h:154: error: expected
constructor, destructor, or type conversion before ?&? token
</error>


Here is the code snippet:

<code>
template <class tData>
class tree
{
public:
//snip
class navigator
{
//snip
public:
navigator();
navigator(const navigator&);
~navigator();

//snip

navigator &operator= (const tree<tData> &);
};

};

//snip

template <class tData>
//the offending line: line 154
tree<tData>::navigator &tree<tData>::navigator:perator= (const tree<tData>
&pointed_node)
{
//snip
}
</code>


Thanks in advance
Rui Maciel

 

[Victor Bazarov]

I'm trying to write a tree class and I've just stumbled on a compiling
problem. The compiler throws an error on a piece of code which to my
eyes it is error-free. Can anyone help me with this?

Here is the error message:

<error>
/home/rui/development/C++/mytree/src/tree.h:154: error: expected
constructor, destructor, or type conversion before ?&? token
</error>


Here is the code snippet:

<code>
template <class tData>
class tree
{
public:
//snip
class navigator
{
//snip
public:
navigator();
navigator(const navigator&);
~navigator();

//snip

navigator &operator= (const
tree<tData> &); };

};

//snip

template <class tData>
//the offending line: line 154
tree<tData>::navigator &tree<tData>::navigator:perator= (const

Add "typename " at the beginning.

tree<tData> &pointed_node)
{
//snip
}
</code>

V

 

[Rui Maciel]

Add "typename " at the beginning.


V

Thanks Victor! That did it. Now it compiles perfecly.

But what's the logic behind the "typename" keyword? Why should it be used in
that situation?


Thanks once again for the help Victor.
Rui Maciel

 

[Sumit Rajan]

Thanks Victor! That did it. Now it compiles perfecly.

But what's the logic behind the "typename" keyword? Why should it be used
in
that situation?

The "typename" keyword, in this case, tells the compiler that navigator is a
type. Without typename, it could be mistaken for a static member of tree.

Regards,
Sumit.

 

[Calum Grant]

Victor Bazarov wrote:




Thanks Victor! That did it. Now it compiles perfecly.

But what's the logic behind the "typename" keyword? Why should it be used in
that situation?

There is the possibility that tree<>::navigator is not a type. Although
tree<>::navigator is defined above, tree<> could possibly be specialized
such that tree<>::navigator did not exist or was something else.

typename reassures the compiler that you really did mean a type, since
tree<>::navigator is technically not defined until point of instantiation.

Hope that makes it clearer?
Calum