Define a variable with the same type as a variable in a struct

Question

In c++ say I have a structure defined in a header file.

******test.h***********
typedef struct mystruct{
    uint8_t num;
} mystruct;

In another header file, say myclass.h, I want to define a variable which has the same type (uint8_t) as the field "num" in mystruct.

******myclass.h***********
class myclass{
public:
    ??? num;
};

Is there a way to define such a variable? Thanks.

Answer 1

Using C++11, you can use decltype:

class myotherclass
{
public:
  decltype (myclass::num) otherNum;
};

Without using C++11, the typical way I have done this is to take a kind of step back. Create a typedef:

typedef uint8_t MyIntegral;

And then use that same type in both classes:

class myclass
{
public:
  MyIntegral num;
};

class motherclass 
{
pulic:
  MyIntegral othernum;
};

This isn't exactly what you were asking for, but if you can change the definition of myclass you may find this approach to be more maintainable.

Answer 2

You have to define the type in your first class, and then access it from the other class

******test.h***********

struct mystruct{
    typedef uint8_t num_t;
    num_t num;
};

And

******myclass.h***********
class myclass{
public:
    mystruct::num_t num;
};