不完整类型的C ++导出模板实现

Question

I have the following scenario:

header.h:

class A
{
    public:

    class B; // incomplete type

private:
    // is never used outside of source file for A
    std::vector<B> vector_of_bs; // template
}

source1.cpp:

class A::B {}; // defined here

All is good until here. Now if I want to use class A elsewhere it doesn't work:

source2.cpp : uses class A and doesn't compile with

vector(721): error C2036: 'A::B *' : unknown size

while compiling class template member function 'std::vector<_Ty> &std::vector<_Ty>::operator =(const std::vector<_Ty> &)'

in VS2010. How can I link against the template specialisation of std::vector in source1.o?

I also need to use this with declspec(_dllimport) ...

Answer 1

Standard library containers cannot be instantiated with incomplete types . To do so is undefined behaviour, and in your case produces a clear error. Other implementations would silently accept your code.

To address this issue, boost provides counterparts for the standard library containers that can in fact be instantiated with incomplete types . You could replace std::vector with the boost counterpart to fix your code:

#include <boost/container/vector.hpp>

class A
{
 public: 
    class B; // incomplete type

 private:
    boost::vector<B> vector_of_bs;
};