CODEWITHSUNDEEP
c++data-structures
tommsch
tommsch

Reputation: 688

Store data of one class in another class

I have a class fp which represents a fixed point number. The underlying type is fixed at compile time, the position of the decimal point is determined at runtime. Thus I need to store the position p of the decimal point somewhere.

Secondly, I want to use my fixed point number in structs which have variables of the fixed-point-number class fp type, including arrays of it ( NB: I am using Cuda, thus, I cannot use std::vector). Since storing the position p inside of the class fp would yield a large overhead, I would like to store it inside of the container structs.

E.g. something like the following (which clearly does not compile)

template<int &p_> struct fp {
    int data;
    float get() { return data/(float)p_; }
    void set( float data_ ) { data = data_*p_; }
};
struct container {
        int p = 4;
        fp<p> s;
};

I have the feeling that my approach is wrong, but I haven´t found another solution yet (I also have have no idea how to title my question --- feel free to edit it).

Upvotes: 0

Views: 299

Answers (1)

MSalters
MSalters

Reputation: 179779

It looks like fp is tied really closely to container. I'd make that really explicit, and make fp a nested type of container. In C++, nesting a type does not create a special relation between instances. That relation between container and fp instances remains the member fp container::s.

But you can now write container accessors that wrap fp::get(), adding fp::d to the argument list of get.

[edit] Since we'd need this in multiple classes, time for a bit of CRTP.

template <typename CT>
class baseContainer 
{
protected:
   struct fp {
     int data;
     float get(int p_) const { return data/(float)p_; }
     void set( float data_, int p_ ) { data = data_*p_; }
  };
  float get(fp const& fp_) { return fp_.get((CT const*)(this)->p_); }
  void set( fp& fp_, float data_) { fp.set(data, (CT*)(this)->p_); }
}

Now container can inherit from baseContainer<container>. In baseContainer<container>, (CT*)(this)->p_ refers to container::p_.

Upvotes: 1

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