Python的Spark自定义Hadoop配置（PySpark）？(Custom Hadoop Configuration for Spark from Python (PySpark)?)

 关键字static在C中已经严重超载，C ++增加了一些额外的含义。 对于static意味着什么的真实讨论，您需要指定上下文：在命名空间范围内， static影响所谓的链接：声明的名称是指不同来源中的同一实体，还是仅涉及这一个特定来源。 在其他地方，对于数据，它指定实体的生命周期， 而不是实体名称的绑定：只有一个静态成员变量的实例，它独立于包含它的类的任何实例而存在。 如果成员函数是静态的，这意味着它没有指向特定实例的指针，并且可以在没有任何实例的情况下调用。 
 
 关于您的具体问题： 
 
 
 
 静态成员不是该类的任何实例的一部分，因此它不会影响类的大小（实际上是其实例的大小）。 静态成员在范围和访问控制方面仍然是成员，但它具有静态生存期，并且存在于类的任何实例之外。 
 
 
 具体对象的sizeof不能为零，因为即使它不包含数据，也不能与内存中的任何其他对象具有相同的地址。 如果定义了这样的对象数组，则第一个元素的地址必须与第二个元素的地址不同（ sizeof返回必须添加到第一个元素的地址以获取第二个元素的地址的字节数） 。 对象的物理大小可以是0，至少在某些情况下：例如，基类的物理大小可以为0（假设它是该类型的唯一基础）。 
 
 
 我不确定你在这里问的是什么。 当你写一些类似ab东西时， b会在a的范围内被查找; 如果b是静态成员，则a仅用于确定范围。 当您编写A::b ， A::还指定将在其中进行名称查找的范围。 
 
 
 从技术上讲，静态数据成员的声明不是定义。 原因，或者至少原因，是它必须独立于类的任何实例而在内存中布局。 在早期，这是当时现有的编译器技术所要求的，即使在今天，您通常也不希望在定义类的头文件中使用初始化数据。 
 

The keyword static was already seriously overloaded in C, and C++ adds a couple of additional meanings. For any real discussion of what static means, you need to specify the context: at namespace scope, static affects what is called linkage: whether the name being declared refers to the same entity in different sources, or only in this one particular source. Elsewhere, for data, it specifies the lifetime of the entity, not the binding of the name of the entity: there is exactly one instance of a static member variable, which exists independently of any instances of the class which contains it. If a member function is static, this means that it has no this pointer to a specific instance, and can be called without any instance.
 
With regards to your specific questions:
 
 
 
A static member is not part of any instance of the class, so it doesn't affect the size of the class (which is in fact the size of its instances). The static member is still a member in terms of scope and access controls, but it has static lifetime, and exists outside of any instance of the class.
 
 
The sizeof of a concrete object cannot be zero, since even if it contains no data, it cannot have the same address as any other object in memory; if you define an array of such objects, the address of the first element must be different from that of the second element (and sizeof returns the number of bytes you must add to the address of the first element to get the address of the second). The physical size of an object can be 0, at least in certain cases: a base class can have a physical size of 0, for example (provided it is the only base of that type).
 
 
I'm not sure what you're actually asking here. When you write something like a.b, b is looked up in the scope of a; if b is a static member, a is only used to determine the scope. When you write A::b, the A:: also specifies thhe scope in which name lookup will occur.
 
 
Techically, the declaration of a static data member is not a definition. The reason, or at least the original reason, is that it must be laid out in memory independently of any instances of the class. In the early days, this was required by the then existing compiler technology, and even today, you generally don't want the initialization data in the header file where you define the class.