How to convert C++ code to C

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Hi everyone,

Could anyone please help me to convert the following C++ code snippet to C code. I have basically zero knowledge in C++ and didn't understand this part.

class DCRemover
{
public:
	DCRemover() : alpha(0), dcw(0)
	{
	}
	DCRemover(float alpha_) : alpha(alpha_), dcw(0)
	{
	}

	float step(float x)
	{
		float olddcw = dcw;
		dcw = (float)x + alpha * dcw;

		return dcw - olddcw;
	}

	float getDCW()
	{
		return dcw;
	}

private:
	float alpha;
	float dcw;
};

What I have tried:

I didn't understand this part of code and couldn't do anything!

Posted 2-Nov-16 19:20pm

Vishnu_Pradeep

Updated 2-Nov-16 22:09pm

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Comments

Suvendu Shekhar Giri 3-Nov-16 1:25am

That's the wrong approach.
Why do you want to convert code of someone which you don't understand?
Why don't to write the required logic in C if you are good at C?

Vishnu_Pradeep 3-Nov-16 1:32am

Thanks for the reply. This is actually a filtering code. Inorder to write it in C, I need to understand what this actually do.

Philippe Mori 3-Nov-16 22:57pm

You could use a debugger or read the first few pages of documentation on C++...

In fact, if you know C and you have an idea of how filtering works, it should be easy to guess what that code do.

Vishnu_Pradeep 5-Nov-16 1:21am

I agree. I was having doubt about the initialisation part, like what exactly this part does DCRemover() : alpha(0), dcw(0)
{
}
DCRemover(float alpha_) : alpha(alpha_), dcw(0)
{
}

I actually wrote the C code myself.

thanks

2 solutions

Solution 1

All it is, is a pair of class level private variables called alpha and dcw, plus a pair of basic functions to manipulate them.
The functions are obvious - they would compile with the two variables declared as global in C - but you can't just robotically translate C++ classes to C code, as each instance of the class that is created is independant, and C has no direct analog of that. You can;t just make the variables global, as you would get just one of each per application, where teh C++ version gets a pair per DCRemover that is created. While you could put them into a struct, that is the trivial part of the problem, because you need the support code to allocate a new struct each time the original code created a DCRemover instance, and you code would have to delete that struct each time the original code had finished with it, as C does not have built in destructors either.

This isn't a good approach: look at the algorithm that the code you found implements, and code that in your C code: it is be a lot simpler and more efficient in the long run.

Posted 2-Nov-16 21:16pm

OriginalGriff

Comments

Vishnu_Pradeep 3-Nov-16 7:35am

Thank you for the response. Is the below code is correct conversion of this?

float DCremoverstep(float x)
{
float alpha=0.99;

float olddcw = dcw;
dcw = (float)x + alpha * dcw;

return dcw - olddcw;
}

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Jochen Arndt · Accepted Answer · 2016-11-02T22:08:00

Solution 2

It looks like a class used by some signal processing loop. Because it is not very complex, it could be also written without class even in C++:

C++

void someProcessFunc(float dcr_alpha)
{
    float alpha, dcw, step, x;
    
    // These two lines together with the local variable
    //  declarations correspond to
    // DCRemover dcr(dcr_alpha);
    alpha = dcr_alpha;
    dcw = 0;

    for (/* iteration conditions*/)
    {
        // x is calculated here or set as part of the for conditions

        // These lines correspond to 
        //  step = dcr.step(x);
        step = -dcw;
        dcw = x + alpha * dcw;
        step += dcw;
    }
}

Posted 2-Nov-16 22:08pm

Jochen Arndt

Comments

Vishnu_Pradeep 3-Nov-16 7:32am

Thanks Jochen. Could you please explain the significance of this?

DCRemover() : alpha(0), dcw(0)
{
}
DCRemover(float alpha_) : alpha(alpha_), dcw(0)
{
}

Jochen Arndt 3-Nov-16 7:49am

They are C++ class constructors. Constructors are special functions that are called when an instance of a class is created. Common usage is to initialise variables and allocate storage.

The above constructors use an initilisation list (a list of member initilisations). But using common assignment is allowed too:
DCRemover() { alpha = 0; dcw = 0; }
DCRemover(float alpha_) { alpha = alpha_; dcw = 0; }

Both versions are used inside a header file. But the implementation can be also moved to a source file:
// Header file
DCRemover();
DCRemover(float alpha_);

// Source file
DCRemover::DCRemover()
{
alpha = 0;
dcw = 0;
}
DCRemover::DCRemover(float alpha_)
{
alpha = alpha_;
dcw = 0;
}

Or again with an initialisation list:
DCRemover::DCRemover(float alpha_) : alpha(alpha_), dcw(0)
{
}

All the above will do the same.

See for example http://www.cplusplus.com/doc/tutorial/classes/

Vishnu_Pradeep 3-Nov-16 8:19am

That is some valuable information. The code is working as expected.
Thanks