C ++类成员的默认值是什么 [英] What is the default value for C++ class members

问题描述

在c ++中，结构的成员和类的成员的默认值是什么，以及这些规则如何不同（例如，在classes / structs / primitives / etc之间）？有没有在默认值的规则不同的情况下？

解决方案

在这方面结构和类之间没有区别C ++ 。它们都只是类类型。

类类型的成员在一般情况下没有默认值。为了使类成员获得确定的值，必须初始化，这可以通过

来完成。

• 
  
• 封装类的构造函数初始化器列表


• 为封装类的对象显式指定初始化器（包括值

此外，具有静态存储持续时间的所有对象在程序启动时都是零初始化。 / p>

除了上述情况，类成员再次没有默认值，并且最初包含不可预测的垃圾值。

What is the default values for members of a struct and members of a class in c++, and how do these rules differ (e.g. between classes/structs/primitives/etc) ? Are there circumstances where the rules about the default values differs ?

解决方案

There are no differences between structs and classes in this regard in C++. They all are called just class types.

Members of class types have no default values in general case. In order to for a class member to get a deterministic value it has to be initialized, which can be done by

• Default constructor of the member itself
• Constructor initializer list of the enclosing class
• Explicitly specified initializer for object of the enclosing class (that includes value-initialization and initialization with aggregate initializer).

Additionally, all objects with static storage duration are zero-initialized at the program startup.

Aside form the above cases, class members, once again, have no default values and will initially contain unpredictable garbage values.

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