Weird syntax error with templates

[James Aguilar]

There is a syntax error in this code that I can't figure out.

template <class T>
std:stream &operator <<(std:stream &os, PriorityQueue<T> &q)
{
using namespace std;

//g++ doesn't like the next line, says error before = operator.
vector< HeapNode< T > >::iterator it = q.m_store.begin();

while (it != q.m_store.end()) {
os << *it++ << endl;
}

return os;
}

The actual error message is:

"PriorityQueue.h: In function 'std:stream& operator<<(std:stream&,
PriorityQueue<T>&)':
PriorityQueue.h:228: error: parse error before '=' token"

Any idea what could be causing it? "HeapNode< T >" is valid when used as a
declaration, and if I change the vector declaration to "vector< int >" it
also works (even though q.m_store is not actually a vector of ints but of
Ts).

Thanks,

James

 

[Victor Bazarov]

There is a syntax error in this code that I can't figure out.

template <class T>
std:stream &operator <<(std:stream &os, PriorityQueue<T> &q)
{
using namespace std;

//g++ doesn't like the next line, says error before = operator.
vector< HeapNode< T > >::iterator it = q.m_store.begin();

'vector<HeapNode<T> >::iterator is not known to the compiler as a type.
The reason is that it is dependent on 'T'. You need to help the compiler
by suggesting that it's a type:

while (it != q.m_store.end()) {
os << *it++ << endl;
}

return os;
}

The actual error message is:

"PriorityQueue.h: In function 'std:stream& operator<<(std:stream&,
PriorityQueue<T>&)':
PriorityQueue.h:228: error: parse error before '=' token"

Any idea what could be causing it? "HeapNode< T >" is valid when used as
a declaration, and if I change the vector declaration to "vector< int >"
it also works (even though q.m_store is not actually a vector of ints but
of Ts).

See inline with quoting.

V

 

[Daniel Mitchell]

There is a syntax error in this code that I can't figure out.

template <class T>
std:stream &operator <<(std:stream &os, PriorityQueue<T> &q)
{
using namespace std;

//g++ doesn't like the next line, says error before = operator.
vector< HeapNode< T > >::iterator it = q.m_store.begin();

while (it != q.m_store.end()) {
os << *it++ << endl;
}

return os;
}

The actual error message is:

"PriorityQueue.h: In function 'std:stream& operator<<(std:stream&,
PriorityQueue<T>&)':
PriorityQueue.h:228: error: parse error before '=' token"

Any idea what could be causing it? "HeapNode< T >" is valid when used as
a declaration, and if I change the vector declaration to "vector< int >"
it also works (even though q.m_store is not actually a vector of ints but
of Ts).

I think you need to add the 'typename' keyword, like so:
typename vector< HeapNode<T> >::iterator

Daniel