In general, it's recommended to pass smart pointers by value.
Passing by value allows the function to take ownership of the pointer if needed (using std::move), or to simply use the pointer without affecting ownership.
#include <memory>
#include <iostream>
void UseResource(std::unique_ptr<int> Resource) {
std::cout << *Resource << '\n';
// Function ends, Resource is destroyed
}
int main() {
auto Resource{std::make_unique<int>(42)};
UseResource(std::move(Resource));
}42Passing by reference is typically used when you want to modify the smart pointer itself, not just the resource it points to.
For example, you might use a reference if you want the function to be able to reset the pointer:
#include <memory>
#include <iostream>
void ResetResource(std::unique_ptr<
int>& Resource) {
Resource.reset(new int{24});
}
int main() {
auto Resource{std::make_unique<int>(42)};
std::cout << *Resource << '\n';
ResetResource(Resource);
std::cout << *Resource << '\n';
}42
24However, these situations are less common. Most of the time, passing by value is sufficient and clearer.
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This Question is from the Lesson:Smart Pointers and
Smart Pointers and std::unique_ptr
An introduction to memory ownership using smart pointers and std::unique_ptr in C++
