在“;”之前修复预期的不合格ID 令牌错误

Question

Rather than compiling, my code is throwing the following error:

expected unqualified-id before ‘;’ token
 template std::list<SGAction_MaxMinMax>::iterator;

I've looked at other threads on similar errors, but none seem to address my problem.

//! Overloaded equality operator
/*!< Returns true if the state and action are the same. */
bool operator==(const SGAction_MaxMinMax & lhs,
                const SGAction_MaxMinMax & rhs);

//! Overloaded comparison operator.
/*!< Returns true if the lhs state is strictly less than the rhs
   state, or if they are equal and the lhs action is strictly less
   than the rhs action/ */
bool operator<(const SGAction_MaxMinMax & lhs,
               const SGAction_MaxMinMax & rhs);

template class std::list<SGAction_MaxMinMax>;
template std::list<SGAction_MaxMinMax>::const_iterator;
template std::list<SGAction_MaxMinMax>::iterator;

The error is on the second to last, and third to last, lines of code above.

Answer 1

template class std::list<SGAction_MaxMinMax>;

This thing is called an explicit template instantination definition . It makes the compiler instantinate std::list<SGAction_MaxMinMax> , and it causes all methods in std::list<SGAction_MaxMinMax> to be compiled, even if they aren't used.

You can read more about this rarely used feature here: Explicit instantiation - when is it used?

---

template std::list<SGAction_MaxMinMax>::const_iterator;
template std::list<SGAction_MaxMinMax>::iterator;

These lines don't look like valid C++ to me. It could be an attempt at explicit instantination as well (but class is missing).

GCC doesn't compile those even if you add class (because apparently list<T>::iterator and const_iterator are type aliases rather than classes).

Simply removing those two lines might work.