Question

in C# I created a static class which had a number of mathematical helper functions I could call directly without creating an instance of the class. I cannot seem to get this to work in C++.

For example, if the class is called MathsClass and has a function called MultiplyByThree then I would use it like this:

float Variable1 = MathsClass.MultiplyByThree(Variable1);

In the C++ version of my code I am getting the errors:

 'MathsClass' : illegal use of this type as an expression

and

 error C2228: left of '.MultiplyByThree' must have class/struct/union

How would I write the C++ equivalent of the C# static class to give this kind of functionality?

Answer 1

The easy answer is to use the :: operator instead of the . operator:

float Variable1 = MathsClass::MultiplyByThree(Variable1); 

But in C++, free functions are generally preferred over static class functions, unless you have a specific reason to put them in a class. For keeping them together, and not polluting the global namespace, you can put them in their own namespace:

In Math.h

namespace Math
{
    float MultiplyByThree(float x);
}

In Math.cpp:

#include "math.h"

namespace Math
{
    float MultiplyByThree(float x)
    {
        return x * 3;
    }
}

And to use it:

#include "math.h"

float Variable1 = Math::MultiplyByThree(Variable1); 

Even better, make it a template and the same code will work for floats, doubles, ints, complex, or any type that has operator* defined:

In Math.h

namespace Math
{
    template <typename T>
    T MultiplyByThree(T x)
    {
        return x * 3;
    }
}

The only issue being that you can’t separate the definition into math.cpp, it has to be in the header.