CODEWITHSUNDEEP
c++
YS_Jin
YS_Jin

Reputation: 55

function pointer point to a member function

I am working on an optimization algorithm, in my algorithm, I need to use a function pointer to pass the function into the optimizer

the class definition:

class Downhill
{
public: //
    Downhill(std::string fpath);
    ~Downhill();
    void run();
private:
    /*objfun will be passed to amoeba function by function pointer*/
    float objfun1(float *p,int ndim);
    float objfun2(float *p,int ndim);
    float objfun3(float *p,int ndim);
    void amoeba(float **p, float pval[], int ndim, float(*funk)(float *, int ndim), float ftol, int &niter);
  
private:

    float ftol;
    float TINY = 1E-10;
    int NMAX = 5000;
    std::ofstream fout;
};

In the declaration of member function run(), I did as:

float(*funk)(float *p, int dim);
funk = &(this->objfun1); // I define the function pointer here
amoeba(p, pval, ndim, funk, ftol, niter);

And I had the compiler errer:

error C2276:  '&': illegal operation on bound member function expression

How can I refer a member function in another member function? Thank you very much!

Upvotes: 0

Views: 90

Answers (1)

user3188445
user3188445

Reputation: 4764

When taking the address of a method pointer, you need to include the name of the class. So in this case, the appropriate syntax would be:

&Downhill::objfun1

At the same time, a non-static method pointer is not interchangeable with a regular function pointer. So you would need to declare the third argument of amoeba as:

float(Downhill::*funk)(float *, int ndim)

And then you would need to call the function as this->*funk(...). If you need to bundle the identity of the object with a pointer, then you might consider making the third argument a std::function<float(float*, int)> (and then using a lambda or std::bind). However in your case that might not be necessary.

Upvotes: 5

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