Question

I’ve had a look through all the similar questions, but this specific scenario doesn’t seem to have come up.

I have a plugin system, where the plugin receives the address of a function to call whenever it wants to insert a hook (which is a class function).

plugin:

struct plugin {
...
    bool (*insert_hook)(hook_data*);
...
};

class:

class manager {
...
    private:
        InsertHook(hook_data *hook);
...
};

creation function in manager:

{
    ...
    typedef bool (manager::*InsertHookFunc)(hook_data*);
    InsertHookFunc    hook_func = &manager::InsertHook;

    // assigning this to the plugin ???
    // C2440, cannot convert from 'hook_func' to 'bool (__cdecl *)(hook_data *)'
    plugin->insert_hook = hook_func;
    ...
}

The manager calls into the plugin, and if the plugin needs to insert any hooks, it needs to call into the manager.

What is the correct method for doing it like this? I know it works normally (the plugin is passed a function pointer to the classes creation function to request a plugin object), but it just seems I can’t assign it due to it being a class function (using a non-class function, this assignment works fine).

I could create a non-class function as a friend to the manager, but I’m sure this can be done directly, I just can’t figure it out…

Answer 1

These types need to match:

typedef bool (manager::*InsertHookFunc)(hook_data*);
bool (*insert_hook)(hook_data*);

The direct fix is to insert another manager:: inside plugin:

bool (manager::*insert_hook)(hook_data*);

The best style is probably to move the typedef outside the class manager like this:

struct manager; // allow manager to be referenced without its definition
typedef bool (manager::*InsertHookFunc)(hook_data*);

struct plugin {
...
    InsertHookFunc insert_hook;
...
};

Or if the plugin already sees the definition of manager, just do

    manager::InsertHookFunc insert_hook;

typedef is definitely your friend when dealing with complicated types.