Error when compiling vector< T >::iterator

[atomik.fungus]

Hi, I'm re-writting my matrix class to practice my programming and the
computer doesn't let me compile the next code: ( this example come
from the constructor of the class)

//the matrix is made of vectors of vectors

template< typename T >
matrix< T >::matrix( unsigned rows, unsigned columns )
{
vector< vector< T > >::iterator p;
....
}

if I change "vector< vector< T > >::iterator p" to "vector< vector<
int > >::iterator p"

then it compiles but it makes the use of templates useless because it
only works now for
matrix < int > (obvious)

the error that i get in the latest g++ is:
error: dependent-name 'std::vector<std::vector<T,
std::allocator<_CharT> >,std::allocator<std::vector<T,
std::allocator<_CharT> > > >::iterator' is parsed as a non-type, but
instantiation yields a type.

Can someone explain me whats happening here and how to fix it.

thanks

 

[peter koch]

Hi, I'm re-writting my matrix class to practice my programming and the
computer doesn't let me compile the next code: ( this example come
from the constructor of the class)

//the matrix is made of vectors of vectors

template< typename T >
matrix< T >::matrix( unsigned rows, unsigned columns )
{
vector< vector< T > >::iterator p;
...

}

if I change "vector< vector< T > >::iterator p" to "vector< vector<
int > >::iterator p"

then it compiles but it makes the use of templates useless because it
only works now for
matrix < int > (obvious)

the error that i get in the latest g++ is:
error: dependent-name 'std::vector<std::vector<T,
std::allocator<_CharT> >,std::allocator<std::vector<T,
std::allocator<_CharT> > > >::iterator' is parsed as a non-type, but
instantiation yields a type.

Can someone explain me whats happening here and how to fix it.

In the line "vector< vector< T > >::iterator p;", the compiler does
not know that the part that becomes before p is the name of a type.
This is because you are allowed to specialise templates, making
iterator a non-type name.
The fix is to prefix the typename with the keyword typename:
typename vector< vector< T > >::iterator p;

Your problem will not occur if you replace T with int because it now
knows the exact type of vector< vector< T > > and thus is aware that
the iterator of that class is indeed the name of a type.

/Peter