C++核心准则C.41:构造函数生成的对象应该被完全初始化

C.41: A constructor should create a fully initialized object
C.41构造函数生成的对象应该被完全初始化

Reason（原因）

A constructor establishes the invariant for a class. A user of a class should be able to assume that a constructed object is usable.

构造函数有责任为类建立不变式。类的用户应该可以假设构造出的对象式可用的。

Example, bad（反面示例）

class X1 {
    FILE* f;   // call init() before any other function
    // ...
public:
    X1() {}
    void init();   // initialize f
    void read();   // read from f
    // ...
};

void f()
{
    X1 file;
    file.read();   // crash or bad read!
    // ...
    file.init();   // too late
    // ...
}

Compilers do not read comments.

编译器不会读注释。

Exception（例外)

If a valid object cannot conveniently be constructed by a constructor, use a factory function.

如果不能方便地通过构造函数构建合法的对象，使用一个工厂函数。

Enforcement（实施建议）

• (Simple) Every constructor should initialize every member variable (either explicitly, via a delegating ctor call or via default construction).

  (简单)所有的构造函数应该初始化所有的成员变量(无论是明确地通过委托构造函数，还是默认构造)

• (Unknown) If a constructor has an Ensures contract, try to see if it holds as a postcondition.

  (不明)如果构造函数包含Ensures协议，尽量确认是否包含了所有的前置条件。

Note(注意)

If a constructor acquires a resource (to create a valid object), that resource should be released by the destructor. The idiom of having constructors acquire resources and destructors release them is called RAII ("Resource Acquisition Is Initialization").

如果构造函数请求了资源(为了生成合法的对象)，那个资源应该被析构函数释放。构造函数申请资源然后析构函数释放它们的做法被称为RAII("资源申请即初始化")。

原文链接

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#c40-define-a-constructor-if-a-class-has-an-invariant

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