What is the difference between references and pointers in C++?

1. Definition: a reference is an alias, a pointer is a variable.
2. Initialization: References must be initialized at declaration and cannot be reassigned to other objects once initialized; pointers can be left uninitialized at declaration and later point to another object.
3. Null value: References cannot point to a null value and must always point to an object; pointers can point to a null value (nullptr).
4. Memory: References do not take up additional memory space, while pointers do take up additional memory space.
5. Operators: references do not have their own operators, whereas pointers do have their own operators, such as the address-of operator (&) and the dereference operator (*).
6. nullptr is the concept of a null pointer, whereas there is no concept of a null reference.

In general, both references and pointers can be used to pass parameters and reference objects, but references are more concise and safe, while pointers are more flexible. It is important to choose the appropriate method based on specific needs and scenarios.