What is the difference between a reference and a pointer in C++?

Difference: 1. The pointer has its own space, and the reference is just an alias; 2. The pointer can point to other objects during use, but the reference can only be a reference to an object and cannot be changed; 3. Pointers can have multiple levels of pointers (eg **p), ​​while references are at one level; 4. The " " operator used by pointers and references has different meanings.

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1. Variable

The first and most important thing is the definition of variable. When you declare a variable, the computer will bind the specified memory space to the variable name; this definition is very simple, but it is actually very abstract, for example : int x = 5; This is the simplest variable assignment statement. Assigning 5 to a memory space named x is essentially assigning the value 5 to a memory space named x.

The operation of variables in memory actually requires two steps:

• Find out the value corresponding to the variable name memory address.

• According to the found address, take out the value in the memory space corresponding to the address and perform operations.

2. Pointers

The special thing about pointers is that the value stored in the memory space corresponding to the pointer variable happens to be a certain memory address. . This is also one of the characteristics that distinguishes pointer variables from other variables. For example, a pointer is defined as follows:

int x = 5;
int *ptr = &x;

ptr is a correction variable name. Obtaining the value in the memory pointed to by this pointer through a pointer is called dereferencing. Null pointers cannot be dereferenced.

The representation of pointer memory space is as follows:

#3. Reference

Reference (reference) in C It is also often used, especially when used as a function parameter and when the value outside the function needs to be modified and updated inside the function. First of all, we must make it clear that a reference is a special kind of pointer.

A reference is a constant pointer pointing to another object, which holds the storage address of the pointed object. And it will be automatically dereferenced when used, without the need to explicitly retrieve it like using a pointer.

For example, the definition of reference is as follows:

int x = 5;
int &y = x;

4. Summary of the difference between pointers and references

• Pointers have their own piece space, and the reference is just an alias;

• Use sizeof to see that the size of a pointer is 4, while the reference is the size of the referenced object;

• The pointer can be initialized to NULL, but the reference must be initialized and must be a reference to an existing object;

• When passed as a parameter, the pointer needs to be dereferenced before the object can be referenced Perform operations, and direct modifications to the reference will change the object pointed to by the reference;

• The pointer can point to other objects during use, but the reference can only be a reference to an object and cannot be Change;

• Pointers can have multiple levels of pointers (**p), ​​while references are at one level;

• Pointers and references use operators The meanings are different;

• If you return an object or memory allocated by dynamic memory, you must use a pointer, and the reference may cause a memory leak.

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