[C++ Series P2] Quote - The Mysterious Assassin of the Backstabbing Pointer (Extensive lecture!)

foreword

• Hello everyone, welcome to the YY drop C++ series, a warm welcome!
• As the title suggests, the main content of this chapter is mainly to "quote " this assassin! The following is the outline~

1. Citation

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1. Meaning and characteristics

References, that is, aliases . Its biggest feature is that the compiler will not open up space for reference variables , they share the same space. 

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2. The difference between references and pointers (mainly) 

1. The reference must be initialized when used .

2. After the reference refers to an entity during initialization , it cannot refer to other entities again , and can only be assigned.

3. References are safer to use .

Graphic:

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3. Practical use of references

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1. References as parameters

When used as an output parameter, when facing large objects/deep copy objects , since there is no need to open up additional space for copying , the efficiency can be improved

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2. Reference as return value  

Small directory:

1. Applicable scene
2. Modify the return value + get the return value (to make the address book code more concise)

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1. Inapplicable scenarios: 

Applicable scenarios: (Stack frames in the static area are not destroyed)

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2. Practical application 

• In the address book, using the traditional method, you need to "find" the corresponding pos position and then "modify"
• And using "reference as return value", you can directly modify the found value. 

Original operation:

Operation after improvement: 

 

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3. Permission issues during citation (panning, zooming out, zooming in) 

1. First of all, we need to know that temporary variables are constant , const modified types are also constant , and static data stored in the static area is also constant .
2. The permissions of const and static are theoretically equal , while the permissions of temporary variables are lower than the two.
3. There can only be a level of authority and reduced authority, and there cannot be a situation of increased authority. In layman's terms: Those with low authority cannot alias those with strong (regular) authority.

Permission-related knowledge points: [ Higher permissions are const and quantities with constant attributes, and lower permissions are ordinary data ]

• Those with high or equal authority can alias/address another quantity ( restriction and translation of authority )
• Those with low authority cannot alias/address another quantity ( enlargement of authority )

Graphic:

1. Situation of flat level and reduced authority

 

 2. Permission translation

 3. Authority amplification

 PS: const cannot be modified in principle, but it can be modified directly by finding its space . (pointer/alias)