General C++ question: Defining a struct within a class

[hipsterdufus]

Hi all, this is a general question about C++. I'm trying to make a Camera class which will contain 2 private member values: an sf::View and a struct containing various camera properties. So basically my idea is, outside this class, you will be able to call Camera.setProperties(<STRUCT CONTAINING DESIRED PROPERTIES>) and that will effectively set up the entire Camera class. So in Camera.h I have my private struct m_CameraProperties. In Camera.cpp I have the definition of that struct - struct Camera::m_CameraProperties{<stuff>};

But when I try to declare my setProperties(<camera properties struct>) it's not letting me use the struct in here. Any ideas? I know I could just ditch a struct and use several variables but I'd like to be able to pass a neat little structure instead of a bunch of random variables. Thanks for any help.

[cpolymeris]

Is your struct definition declared public in your headerfile?

class Camera
{
//...
public:
  struct CameraProperties
  {
      int somethingsomething;
      float thisandthat;
  };
//...
};
 

[hipsterdufus]

I think I figured out how to define it:

I have it defined as private in the Camera headerfile like so:

Code: [Select]

struct m_CameraProperties;
Then in the .cpp file I can define it like so:

Code: [Select]

struct Camera::m_CameraProperties{

bool IsYLocked;
bool IsXLocked;
float YMinimum;
float XMinimum;
float YMaximum;
float YMinimum;

};
Still trying to figure out how to declare it as a parameter in a Camera member function...

[Laurent]

What is the error message?

Keep in mind that:
- you must declare the structure before the function that uses it
- if the function takes the struct argument by copy, the full definition must be in the header, not only the forward declaration (struct m_CameraProperties)

By the way, m_CameraProperties is a strange name for a type; usually the m_ prefix is for member variables.

[cpolymeris]

If you want to use it as a parameter, the definition must be public (in the headerfile), the declaration can be private (in the headerfile, too, but instantiated in the cpp if it is static).

//Camera.hh
class Camera
{
public:
  struct CameraProperties
  {
//...
  };

private:
   CameraProperties properties;

public:
  void someMethod(const CameraProperties &);

};
 

How else are the  consumers of the class going to know what to pass to your method?

[hipsterdufus]

I would think there's a way to keep it a private member. I'm getting confused now as to what's the type definition and where's the variable definition...I will read up on the basics of defining structs I guess. They have always confused me as I've seen them declared with typedef and sometimes they are not. Now with the extra layer of being within a class I'm extra confused.

Anyways I think I'm getting closer:

Camera.h

class Camera
{
public:
        Camera();
        ~Camera();

        void setProperties(Camera::TCameraProperties* cameraProperties); // Still complains saying Camera has no member TCameraProperties
       

private:

        struct TCameraProperties;
        TCameraProperties* m_CameraProperties;

        sf::View m_View;

};

 

Moving the struct defs to public doesn't make a difference.

[hipsterdufus]

Hah, you're right...actually it works if I move the function below the private: declarations...unbelievable.

[zsbzsb]

Hah, you're right...actually it works if I move the function below the private: declarations...unbelievable.

To quote Laurent...

Keep in mind that:
- you must declare the structure before the function that uses it
- if the function takes the struct argument by copy, the full definition must be in the header, not only the forward declaration (struct m_CameraProperties)