Re: Declaring a static const member of a class.
On Mar 2, 7:26 pm, Luca Cerone <luca.cer...@gmail.com> wrote:
Dear all,
I'm having a few difficulties in declaring a class with a static constant=
member.
This member is a vector of double that has to be created once during
the execution and shared among all the objects.
After being created it can't be modified during the whole execution of my=
program.
I write a toy example to show you what I'd like to do (it doesn't work,
but I can't figure out a way to code it well, that's why I'm posting here=
).
#include<iostream>
#include<vector>
class QuadFun{
public:
QuadFun(double a, double b) ; // a and b will be used to initiali=
ze
// the private vector y to evaluate the values (x-a)*(x-b)
// x has to be a vector that is shared among all the object of th=
e class.
private:
static const std::vector<double> x; // this will be a vector of u=
niformly
//spaced numbers from 0 to 1. The number of points=
is determined
//by reading a configuration file. in this example=
I set the
//number manually in the main function.
std::vector<double> y;
}
int main() {
int numPoints=50; // this value is actually read from a configurati=
on file
// here is the problem. I don't want the number of points to be a mem=
ber
// of the class.
QuadFun f1=QuadFun(0,1);
QuadFun f2=QuadFun(0.5,0.75);
// how can I make the vector x mad of numpoints created when I first =
create
// an object of class QuadFun?
// how can I make it "dynamic" so that if I change the value of numPo=
ints
// the x vector will be created accordingly? (in an other execution).
return 0 ;
}
Hope I could explain well what I'd like to achieve.
I know this code is WRONG, but I can't understand how to write it
in a good way.
Can you help me?
Thanks a lot in advance,
Cheers, Luca
Hello
My pretty quick solution:
// quad_fun.h
#include<vector>
class QuadFun{
public:
QuadFunc(double a, double b);
const std::vector<double> GetY() const { return y; }
static bool filled; // to make sure, we filled x already
private:
static std::vector<double> x;
static void FillX(); // static member function for filling X
std::vector<double> y;
};
// quad_fun.cpp
#include "quad_fun.h"
using std::vector;
vector<double> QuadFun::x;
bool QuadFun::filled = false;
extern int numPoints;
QuadFun::QuadFun(double a, double b)
{
FillX();
y.clear();
for (vector<double>::size_type i = 0; i < x.size(); ++i)
y.push_back((x[i] - a) * (x[i] - b));
}
void QuadFun::FillX()
{
if (!filled)
for (int i = 0; i < numPoints; ++i)
x.push_back(i % 3 + 0.0); // fill with 0 or 1, just an example
filled = true;
}
// quad_fun_main.cpp
#include "quad_fun.h"
#include <iostream>
#include <algorithm>
#include <iterator>
int numPoints; // this value is actually read from a configuration
file
int main() {
using namespace std;
cout << "Number of points ";
cin >> numPoints;
QuadFun f1= QuadFun(0,1);
vector<double> y = f1.GetY();
copy(y.begin(), y.end(), ostream_iterator<double>(cout, "\t"));
cout << '\n';
QuadFun f2=QuadFun(0.5,0.75);
y = f2.GetY();
copy(y.begin(), y.end(), ostream_iterator<double>(cout, "\t"));
return 0 ;
}
HTH,
-- Saeed Amrollahi Boyouki