TObject包含什么数据？ [英] What data does a TObject contain?

问题描述

TObject.InstanceSize返回8，但TObject不声明任何数据成员。根据TObject.ClassType的实现，前4个字节可以解释为指向对象的TClass元数据的指针。任何人都知道其他4个字节的开销是什么？

TObject.InstanceSize returns 8, yet TObject doesn't declare any data members. According to the implementation of TObject.ClassType, the first 4 bytes can be explained as a pointer to the object's TClass metadata. Anyone know what the other 4 bytes of overhead are there for?

编辑：显然这是D2009特有的。在旧版本中，只有4个字节。

Apparently this is specific to D2009. In older versions, it's only 4 bytes.

推荐答案

在Delphi 2009中，有

In Delphi 2009, there is the ability to have a reference to a synchronization monitor. See:

class function TMonitor.GetFieldAddress(AObject: TObject): PPMonitor;
class function TMonitor.GetMonitor(AObject: TObject): PMonitor;

...在System.pas中

...in System.pas

此外，还有一个指向VMT的指针。 （虚拟方法表。）从中的Delphi简介：

Also, there is still a pointer to the VMT. (Virtual Method Table.) From Delphi in a Nutshell:

TObject类声明了几个
方法和一个特殊的隐藏字段
来存储对对象的
类。这个隐藏的字段指向
类的虚拟方法表（VMT）。
每个类都有一个唯一的VMT，该类的所有
对象共享
类的VMT。

The TObject class declares several methods and one special, hidden field to store a reference to the object's class. This hidden field points to the class's virtual method table (VMT). Every class has a unique VMT and all objects of that class share the class's VMT.

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