Question

I have the following struct to manage Camera State with

 struct keyState
 {
    float x_rotation, y_rotation, z_rotation;
    float x_rotation_rad, y_rotation_rad, z_rotation_rad;
    float x_pos, y_pos, z_pos;
 } state_manager;

This struct is located in my WalkingCameraManipulator.h class. WalkingCameraManipulator is implemented in WalkingCameraManipulator.cpp, and I have an #include “WalkingCameraManipulator” in my main class.

Error 1 error LNK2005: “struct keyState state_manager” (?state_manager@@3UkeyState@@A) already defined in main.obj
Error 2 error LNK1169: one or more multiply defined symbols found

However, I am dealing with the following error message and need to find the best place for my struct. Any ideas on what I can do here? Thanks in advance.

Answer 1

The trailing state_manager defines an instance. In a header. Which is wrong. I suggest you refactor your code as:

struct keyState
 {
    float x_rotation, y_rotation, z_rotation;
    float x_rotation_rad, y_rotation_rad, z_rotation_rad;
    float x_pos, y_pos, z_pos;
 } ;

extern keyState state_manager;

//somecppfile.cpp
keyState state_manager;

The extern part is a declaration, and the definition is now in a single implementation file. This mimics your intended behavior, but is probably not what you really want. Do you really want a global instance of keyState? If not, remove it alltogether:

struct keyState
 {
    float x_rotation, y_rotation, z_rotation;
    float x_rotation_rad, y_rotation_rad, z_rotation_rad;
    float x_pos, y_pos, z_pos;
 } ;