Boost.Test check whether a pointer is null

Question

I have the following test :

BOOST_CHECK_NE(pointer, nullptr);

The compilation fails due to

/xxx/include/boost/test/tools/detail/print_helper.hpp:50:14: error: ambiguous overload for ‘operator<<’ (operand types are ‘std::ostream {aka std::basic_ostream}’ and ‘std::nullptr_t’)

What is wrong and how should I test for null pointers ?

Answer 1

The easiest check for a pointer being non-null is this:

BOOST_CHECK(pointer);

A null pointer implicitly converts to false, a non-null pointer implicitly converts to true.

As to what the problem with your use case is: nullptr is not a pointer type, it's of type std::nullptr_t. It can be converted to any pointer type (or pointer to member type). However, there is no overload of << for inserting std::nullptr_t into a stream. You would have to cast nullptr to the appropriate pointer type to make it work.

Answer 2

As mentioned in error message, nullptr has ambiguous overloads.

BOOST_CHECK(pointer);

or

BOOST_CHECK_NE(pointer, static_cast<decltype(pointer)>(nullptr));

should do the job.