trying to declare an iterator for a std::vector of template pointers

[Ken Cecka]

This is a contrived example to demonstrate a syntax problem I'm struggling
with:

#include <vector>

template <typename T>
class Class
{
};

template <typename T>
class Container
{
public:
typedef Class<T> * ClassPointer;
typedef std::vector<ClassPointer> ClassVector;
typedef ClassVector::iterator ClassVectorIterator;
};

int main(void)
{
return 0;
}

When I compile this code using g++ v3.4.1, I get the following errors:
/home/ceckak/test.cpp:16: error: type `std::vector<Class<T>*,
std::allocator<Class<T>*> >' is not derived from type `Container<T>'
/home/ceckak/test.cpp:16: error: ISO C++ forbids declaration of `iterator'
with no type
/home/ceckak/test.cpp:16: error: expected `;' before "ClassVectorIterator"

If I change the ClassPointer typedef to the following, the error goes away
typedef Class<int> * ClassPointer;

Or if I make Class a regular (non-template) class, the error goes away.

Or if I comment out the iterator typedef, the code compiles without errors.

Can anyone tell me if/how to declare an iterator to a vector of template
pointers?

Thanks in advance for any help!

Ken

 

[Malte Starostik]

This is a contrived example to demonstrate a syntax problem I'm struggling
with:

#include <vector>

template <typename T>
class Class
{
};

template <typename T>
class Container
{
public:
typedef Class<T> * ClassPointer;
typedef std::vector<ClassPointer> ClassVector;
typedef ClassVector::iterator ClassVectorIterator;

typedef typename ClassVector::iterator ClassVectorIterator;

};

int main(void)

int main()
// (void) to denote an empty argument list is C-ish

{
return 0;
}

When I compile this code using g++ v3.4.1, I get the following errors:
/home/ceckak/test.cpp:16: error: type `std::vector<Class<T>*,
std::allocator<Class<T>*> >' is not derived from type `Container<T>'
/home/ceckak/test.cpp:16: error: ISO C++ forbids declaration of `iterator'
with no type
/home/ceckak/test.cpp:16: error: expected `;' before "ClassVectorIterator"

Prior versions of gcc have accepted the code, but warned about implicit
typename being deprecated. Now it rejects the code completely, in full
accord with the standard.

If I change the ClassPointer typedef to the following, the error goes away
typedef Class<int> * ClassPointer;

Because then ClassVector is no longer dependent on the template parameter T.

Or if I make Class a regular (non-template) class, the error goes away. Dito.

Or if I comment out the iterator typedef, the code compiles without errors.

Obviously

Can anyone tell me if/how to declare an iterator to a vector of template
pointers?

Tell the compiler that ClassVector::iterator is a type name as I did above.

HTH,
Malte

 

[Steffen Jakob]

Am Sun, 27 Mar 2005 11:48:35 -0800 schrieb Ken Cecka:

#include <vector>

template <typename T>
class Class
{
};

template <typename T>
class Container
{
public:
typedef Class<T> * ClassPointer;
typedef std::vector<ClassPointer> ClassVector;
typedef ClassVector::iterator ClassVectorIterator;
};

int main(void)
{
return 0;
}
//
Can anyone tell me if/how to declare an iterator to a vector of template
pointers?

Yes:

typedef typename ClassVector::iterator ClassVectorIterator;

Thanks in advance for any help!

Greetings,
Steffen.

 

[Ken Cecka]

typedef typename ClassVector::iterator ClassVectorIterator;
int main()
// (void) to denote an empty argument list is C-ish

Prior versions of gcc have accepted the code, but warned about implicit
typename being deprecated. Now it rejects the code completely, in full
accord with the standard.

Because then ClassVector is no longer dependent on the template parameter
T.

Obviously

Tell the compiler that ClassVector::iterator is a type name as I did
above.

HTH,
Malte

Thanks both of you for the quick response. Adding typename solved the
problem. I'll have to do a little more reading up on when typename is
required, but I think I get the gist of it.

Ken