I am learning c++, recently i read a book which gives a suggestion that you should use reference to const when possible (if base object will not be changed).
I have a question that should you pass reference to const pointer instead of const pointer, when possible, as reference prevents copied. If not when should i use reference to const pointer.
e.g:
Node(..., Node *const next = nullptr);
OR
Node(..., Node* const& next = nullptr);
Passing by const reference is good practice when passing by value (that causes copying of parameters) is a heavy operation.
For example when you are passing a class with some properties to a function it's better to pass it by const reference, In other hand if your are passing types like int or just a pointer it's better not to use references because then you loos performance due to de-reference process.
Since references essentially are pointers there is no performance gain in passing pointers by reference.
You would only ever use a reference to a pointer if your intention was to modify the pointer value. For example:
ErrorCode MakeSomeObjectForMe(Object *&ptr) {
if (badPreCondition) {
return SomeSpecificError;
}
ptr = new Object();
return Succuess;
}
// Use ptr outside the function.
Otherwise it is not a good idea because it may cost you in performance through double indirection. So you will likely never pass a const & to a pointer.
As one example, in concurrent programming passing a ref to const ptr to worker thread may be used as a communication means; the ptr might be actually not const.
mutex sync;
void task(int*const&);
int main(){
int *paramptr=nullptr;
thread woker{task,paramptr};
sync.lock();
paramptr=whatever;
sync.unlock();
worker.join();
return 0;
}
