Question

My situation is following, I have two different bisection functions what will be called at some point in my code. Basically some function calls Bisection2 and this function calls either the passed function or it passes the function pointer to Bisection function.

in header I have

std::vector<double> F();
double F1(double m1, double m2);
double F2(double m1, double m2);
typedef double (MyClass::*MyClassFn)(double,double);
double Bisection(MyClassFn fEval,double min, double max,std::vector<double> args);
bool Bisection2(MyClassFn fEval1,MyClassFn fEval2,double xmin, double xmax, double ymin, double ymax,double *ax, double *ay,std::vector<double> args);

And my bisection functions look like this. I didn’t include all the code because it’s not necessary.

double MyClass::F1(double m1, double m2) {
    m_m1 = m1;
    m_m2 = m2;
    F();
    return m_my;
}

double MyClass::F2(double m1, double m2) {
    m_m1 = m1;
    m_m2 = m2;
    F();
    return m_mx;
}
double MyClass::Bisection(MyClass fEval,double min, double max,std::vector<double> args)
{
    // Setting a lot of stuff here, including auxiliary and leftvalue...

    MyClass *pObj = new MyClass(-1);

    leftvalue = pObj->*fEval(auxiliary, left);
    ightvalue = pObj->*fEval(auxiliary, right);

    // Comparing and setting values here etc.
}
bool MyClass::Bisection2(MyClassFn fEval1,MyClassFn fEval2,double xmin, double xmax, double ymin, double ymax,double *ax, double *ay,std::vector<double> args)
{

    // Setting some values here but these have nothing to do with the problem.
    double yl;
    double leftvalue, rightvalue, middlevalue;

    MyClass *pObj = new MyClass(-1);

    // Setting some values here but these have nothing to do with the problem.
    std::vector <double> arg;
    // pushing some values

    yl = Bisection(fEval2,ymin,ymax,arg); // Here is the first way how I need to pass fEval2 to Bisection function.
    arg.clear();

    if(isnan(yl))
    {
        return M_NAN;
    }
    leftvalue = pObj->fEval1(xl, yl); // And here is the second way how I need to use fEval1.

//.....
}

And then I have basically a function what calls

`Bisection2(F1,F2, m_m2,0.0, 0.0, m_max2, &m_mu1, &m_mu2,args);

The Bisection2(…) call may be incorrect at the moment because I’ve changed the functions a lot since this worked last time. Last time I basically called F1 and F2 function pointers directly inside the functions instead of fEval’s but I’m quite sure it was incorrect way after all even thought it seemed to work somehow.

Now leftvalue = pObj->*fEval(auxiliary, left); causes compiling errors:

error: must use ‘.*’ or ‘->*’ to call pointer-to-member function in ‘fEval (...)’, e.g. ‘(... ->* fEval) (...)’

I’ve tried to see help from here http://www.parashift.com/c++-faq-lite/pointers-to-members.html#faq-33.2
and also checked maybe different solved problems in these forums but still can’t figure out what I’m doing wrong.

Thank you.

Answer 1

As the error message says, you need parentheses. This is because the function call has higher precedence than the ->* operator:

leftvalue = (pObj->*fEval)(auxilary, left);
            ^            ^

Also, you almost certainly shouldn’t be using new here; you can fix the memory leaks using automatic storage:

MyClass obj(-1);
leftvalue = (obj.*fEval)(auxiliary, left);