Question

I am new to function pointers and I would like your help.
I am having a method:

int test3(int i)
{
    return i;
}

Then in another method(not main) I do:

int (*pTest3)(int) = test3;

From the examples that I have read this seems ok.
However, I get a compile time error:

testFile.cpp:277:25: error: argument of type ‘int
({anonymous}::CheckingConsumer::)(int)’ does not match ‘int (*)(int)’

I do not understand what is wrong. Any help would be appreciated.

Thanks a lot.

Answer 1

Your test3 is a member function of a struct or a class. Class member functions have a hidden this parameter passed into them and so cannot be used with plain function pointers. You need to either declare the function as static or move it outside the struct/class, so that it no longer has a hidden this parameter, or use a class method pointer instead of a function pointer:

// static class method:
class X
{
    static int test3(int i)
    {
        ...
    }
};

// Non-class method, at global scope
int test3(int i)
{
    ...
}

// Class method pointer
class X
{
    int test3(int i)
    {
        ...
    }
};

// Create the method pointer
int (X::*pTest3) = &X::test3;
X *obj;
// Call the method pointer on an object
(obj ->* pTest3)(42);