why I cannot use forward declaration when using template？

Question

for non-template class, I can use forward declaration in the header file. But it gave me error when I use it in the template class.

I have to include the header file, I would like to know the reason.

class Pu;

template <typename T>
class Pt()
{
     void test(Pu<T> u);
}

I believe you're looking for this: http://stackoverflow.com/questions/495021/why-can-templates-only-be-implemented-in-the-header-file — Angew is no longer proud of SO, Feb 10 '15 at 14:25
This syntax for forward declaration works: `template class MyClass;` - did you intend to use anything else? — anatolyg, Feb 10 '15 at 14:35

score 6 · Accepted Answer · answered Feb 10 '15 at 14:42

It works just fine, if you do it properly!

Remember, Pu is a class template, not a class, so it must be declared as such:

template <typename T>      // N.B. this line
class Pu;

template <typename T>
class Pt                   // N.B. no "()"
{
     void test(Pu<T> u);
};                         // N.B. ";"

why I cannot use forward declaration when using template？

1 Answers1

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