如何在 C++ 模块中使用全局变量？

问：

当我在 C++20 项目中使用模块时，如果我有

// Camera.hpp
extern const unsigned int SCR_WIDTH;
extern const unsigned int SCR_HEIGHT;

在主.cpp中

const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

但是现在我使用模块，

// Camera.cppm
module;

#include <glad/glad.h>
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>

export module Camera;

// extern const unsigned int SCR_WIDTH;
// extern const unsigned int SCR_HEIGHT;

链接器似乎找不到变量，那么我应该如何修改它呢？

ld.lld: error: undefined symbol: SCR_HEIGHT@Camera
>>> referenced by CMakeFiles/triangle.dir/src/triangle2.cpp.obj:(.refptr._ZW6Camera10SCR_HEIGHT)

ld.lld: error: undefined symbol: SCR_WIDTH@Camera
>>> referenced by CMakeFiles/triangle.dir/src/triangle2.cpp.obj:(.refptr._ZW6Camera9SCR_WIDTH)