How to make void (**)() from void()?

Have function:

void btCallback(esp_spp_cb_event_t event, esp_spp_cb_param_t *param) { 
  // ...
}

Need to use in:

BT.register_callback(btCallback);

Compiler error:

no known conversion for argument 1 from 'void(esp_spp_cb_event_t, esp_spp_cb_param_t*)' to 'void (**)(esp_spp_cb_event_t, esp_spp_cb_param_t*)'

As I understand it, he needs a pointer to function pointer. I don’t know how to create it. I tried a function pointer (through &), does not fit.

P.S. Is arduino-esp32 BluetoothSerial::register_callback function.

>Solution :

You need to make a pointer variable, and then take a pointer from it using the & operator.

void f()
{
    // ...
}

void g(void (**p)())
{
    // ...
}

int main()
{
    void (*f_ptr)() = f;
    g(&f_ptr);
}

Try if here.

As I understand it, he needs a pointer to function pointer. I don’t
know how to create it. I tried a function pointer (through &), does
not fit.

In the previous example, taking &f doesn’t have any effect. These two lines are equivalent!:

void (*f_ptr)() = f;
void (*f_ptr)() = &f;

Therefore, if you were doing:

g(&f);

you are actually passing a simple function pointer, not a pointer to function pointer.