constant member in class - c++

Question

I have this class:
class model
{
private:
link_list list;
float parameter_B1;
float parameter_B0;
public:
model();
float getparameter_B1() const;
float getparameter_B0() const;
float predict();
void info();
};
In which float parameter_B1 and float parameter_B0 are constant , but in order to initialize them , I have to enter constructor body and read a file and using that file's data to find value of these two attributes, but once I set them ,they won't change again.(so I guess they are count as constant)
like this:
model::model()
{
char filename[300];
cout << "enter file name(path\\filname.txt):" << endl;
cin >> filename;
FILE* fp;
fp = fopen(filename, "r+");
float x, y;
if (fp == NULL)
{
cout << "Unable to open the file!" << endl;
exit(EXIT_FAILURE);
}
else
{
while (!feof(fp))
{
if (fscanf(fp, "%f\t%f", &x, &y) == 2)
{
Pair p(x, y);
list.insertNewNode(p);
}
}
}
Pair _average = list.average();
parameter_B1 = list.parameters1(_average);
parameter_B0 = list.parameters2(_average, parameter_B1);
}
but if I change my class to:
class model
{
private:
link_list list;
const float parameter_B1;
const float parameter_B0;
public:
model();
const float getparameter_B1() const;
const float getparameter_B0() const;
float predict();
void info();
};
I will receive these error "model::model()" provides no initialize for:
1. const member "model::parameter_B1"
2. const member "model::parameter_B0"
, but as you can see I can't use initializer list.
what should I do? is not declaring constant variable my only solution?

Answer 1

with delegating constructor, you might do
std::tuple<link_list, float, float> read_model_file()
{
char filename[300];
cout << "enter file name(path\\filname.txt):" << endl;
cin >> filename;
// ...
Pair _average = list.average();
parameter_B1 = list.parameters1(_average);
parameter_B0 = list.parameters2(_average, parameter_B1);
return {std::move(list), parameter_B0, parameter_B1};
}
class model
{
private:
link_list list;
const float parameter_B0;
const float parameter_B1;
public:
model() : model(read_model_file()) {}
model(std::tuple<link_list, float, float> t) :
list(std::get<0>(std::move(t))),
parameter_B0(std::get<1>(std::move(t))),
parameter_B1(std::get<2>(std::move(t)))
{}
// ...
};