如何导入/导出C++模板类

Question

当模板类在共享库和静态库中编译时，我如何使用和消费它？

例如，我有一个库项目：

/// Lib/Config.hpp
// if building a shared library
#ifdef LIB_BUILD_DLL
#  define LIB_API          __declspec(dllexport)
#  define LIB_TEMPLATE_API __declspec(dllexport)
#  define LIB_EXTERN
// exe projects use the shared library
#elif defined(LIB_DLL)
#  define LIB_API          __declspec(dllimport)
#  define LIB_TEMPLATE_API
#  define LIB_EXTERN       extern
// if building a static library, and exe projects use the static library
#else
#  define LIB_API
#  define LIB_TEMPLATE_API
#  define LIB_EXTERN
#endif
/// End of Lib/Config.hpp

/// Lib/Location.hpp
template<typename T>
LIB_EXTERN class Vector2;

class LIB_API Location
{
public:
     Vector2<float> point;
};
/// End of Lib/Location.hpp

/// Lib/Vector2.hpp
template<typename T>
LIB_EXTERN class LIB_TEMPLATE_API Vector2
{
public:
    template <typename U>
    explicit Vector2(const Vector2<U>& vector)
    {
        x = vector.x;
        y = vector.y;
    }

    Vector2<T> operator -(const Vector2<T>& right)
    {
        return Vector2<T>(x - right.x, y - right.y);
    }

    T x;
    T y;
};
typedef Vector2<float> Vector2f;
/// End of Lib/Vector2.hpp

和一个exe主项目：

#include "Lib/Config.hpp"
#include "Lib/Location.hpp"
#include "Lib/Vector2.hpp"

class Application
{
public:
    Location location_;
    Vector2<float> point_;
    Vector2f float_point_;
}

我想问的是，我是否正确地使用了LIB_EXTERN？

如何将Vector2f对象传递给复制构造函数Vector2(const Vector2<U>& vector)

Answer 1

通常不会导出模板函数或类。它们针对每个翻译单元进行编译，并在必要时由链接器进行清理。只需包含.hpp文件，就可以在需要的地方编译必要的代码。