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This article introduces the knowledge of "when to use class in C++". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

C.2: classes containing invariants use class to define classes, and struct to define classes if data members can be changed independently.

Translator's note: an invariant can be regarded as a condition that a member of a class must meet. For example, for std::string, the length member must be equal to the length of the string it manages.

Reason (reason)

Readability. Reduce the difficulty of understanding. Using the class keyword makes programmers aware of the need for invariants. This is a useful practice.

Translator's note: the use of the class keyword also ensures by default that data members will not be modified at will, which makes it possible to maintain invariants.

Note (Note)

Invariants are the logical conditions that members of an object must satisfy. These conditions are established by constructors and are the prerequisites of public member functions. Once the invariant is established (usually by the constructor), all member functions of the object can be called. Invariants can be informally specified (for example, through comments) or formally checked by Expects (antecedent conditions).

If all data members can be changed independently of each other, there can be no invariants.

Example (sample)

Struct Pair {/ / the members can vary independently string name; int volume

}

But:

Class Date {public: / / validate that {yy, mm, dd} is a valid date and initialize Date (int yy, Month mm, char dd); / /... private: int y; Month m; char d; / / day}

Translator's note: the invariant of this example is that the combination of year, month and day must be valid.

Note (Note)

If a class contains private data members, the consumer cannot fully initialize the object of the class without using the constructor. Therefore, the definer of a class must define its meaning while providing the constructor. This actually means that the definer needs to define invariants.

See also (see):

Define a class with private data as class

Use the class keyword to define a class that contains private data.

Prefer to place the interface first in a class

It is recommended that you define the interface at the beginning of the class

Minimize exposure of members

Minimum exposure of members

Avoid protected data

Avoid protected type data

Enforcement (implementation recommendations)

Look for structs with all data private and classes with public members.

Find all data structures that are defined as private and classes that contain public members.

Translator's note: the so-called principles are those good practices that can be implemented without deep thinking, but the effect will gradually become apparent.

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