Differences between the use of structs and classes

Some time ago, I encountered a problem when writing thrust superposition , At first, I used two lists to store the speed obtained by thrust and direction respectively 、 Duration of speed , Subscripts correspond to each other . Later, I felt that I could use structures to store speed and duration , In this way, you only need a list management , You can use less than one traversal , At the same time, better object-oriented . Then when I use the structure to change, I find that the fields in the structure cannot be directly used for addition, subtraction and other operations , Because the fields in the structure are placed on the stack , Value type . Later, the structure was changed into a class to solve this problem , Because classes are stored in the heap , Is the reference type . So I want to summarize the difference between the two ：

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1. Structure field cannot be initialized , The fields of class can be initialized

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2. A structure is a value type , Store on stack ; Class is a reference type , Store in the pile

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3. Structs can no longer write parameterless constructors , Classes can be ; However, you can write constructors with parameters

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4. All fields must be assigned values in the constructor of the structure , Classes do not have to be assigned all

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5. Structures create objects in a somewhat different way

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6. To sum up , When to use ？

（1） Structures are stored on the stack , and Stack has 1 Characteristics , It's just that the space is small , But the access speed is faster , Large heap space , But the access speed is relatively slow . So when we describe 1 When a lightweight object , It can be defined as a structure to improve efficiency . For example , rectangular , Color , These objects are lightweight objects , Because describing them , Only a few fields are needed . When describing 1 When you're a heavyweight object , We know that class objects are stored in heap space , We define the heavyweight object as a class . Although they can contain data structures of data members and function members , But the difference between structs and classes is , The structure is a value type and does not require heap allocation , The variables of the structure directly contain the data of the structure , The variables of the class contain references to data .
（2） When we pass values to variables , I just want to pass a copy of the object , Not the reference address of the object , Then you can also use the structure at this time .
（3） I see some places where structures are used in projects , Generally, it is the place where the field is pure quantity or pure string , So an object is a pure data type , No complicated method 、 Logic 、 Structure can be considered for operation . This is the main reason for using structures at present , There is also a structure in the editor （ such as Unity） It will be more convenient to display on .