C++ function pointer to non static member function [duplicate]

Question

I have 2 classes: MeshInput and VoxelGrid. VoxelGrid has the member sdf which is a function pointer. Now I want to assign a non static function of another class to sdf. I can't change the signature of either because sdf also sometimes points to a function outside of MeshInput. How do I do that?

Code below:

class VoxelGrid {
 private:
  double (*sdf)(tg::pos3 const&);
}

class MeshInput {
 public:
  double sdfFromMesh(tg::pos3 const& point);
}

From my understanding the Issue is that when calling the function with the function pointer there is no implicit this* pointer like when calling it from an object (A.sdfFromMesh()). But I don't know how to work around that.

You cannot do this. Non static member function doesn't have double (tg::pos3 const&) signature, its first argument is a pointer to the object. Can you change your raw pointer to std::function<double(tg::pos3 const&)> ? — pptaszni
– pptaszni, Commented Nov 16, 2023 at 9:42
theres no way to work around. If you want to call a non static member function you need an object. You could bind the object together with the member function pointer though — 463035818_is_not_an_ai
– 463035818_is_not_an_ai, Commented Nov 16, 2023 at 9:47
How can I pass a member function where a free function is expected? — Richard
– Richard, Commented Nov 16, 2023 at 10:47

Austin Yang · Accepted Answer · 2023-11-16 10:37:56Z

0

You can use std::function cooperate with std::bind.

std::bind can specific target function to be kept and where it belong. For example:

struct Foo
{
    double get(tg::pos3 const&) { return 0; }
};

Then you can bind get to your variable like this:

std::function<double ( tg::pos3 const& )> sdf = std::bind(&Foo::get, &YourFooObj, std::placeholders::_1)

see std::bind and std::function for more detail.

answered Nov 16, 2023 at 10:37

Austin Yang

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