What is the memory layout of C++ objects?
This article mainly explains "what is the memory layout of C++ objects". The content of the explanation in this article is simple and clear, and it is easy to learn and understand. let's go deep into the editor's train of thought. Let's study and learn how the memory layout of C++ objects is.
Simple non-polymorphic memory layout
Class X {int x; float xx;public: X () {} ~ X () {} void printInt () {} void printFloat () {}}; |-| printZ (); / / Not OK, as virtual table of class Y doesn't have address of printZ () method
In the above code, y_ptr points to a child of class Y within the complete Z object.
As a result, call any method, such as using yroomptra-> printY (). The resolution method for using y_ptr is as follows:
(* yroomptra-> _ vtbl [2]) (y_ptr)
Virtual inheritance memory layout
Class X {int x;}; class Y: public virtual X {int y;}; class Z: public virtual X {int z;}; class A: public Y, public Z {int a;}
The layout is as follows:
| | Y class-> |-| |-| |-> |-| sub-object | Zpurpurz | |. |-|-| | Z::_vptr_Z |-| |-| A sub-object-- > | offset of X |-| offset of X | / / offset (12) starts from Z X class-> | XRV starts from Z X class | |-> |-| shared |-| |. | | sub-object |-| |
The memory representation of a derived class with one or more virtual base classes is divided into two regions: an invariant region and a shared region.
The data in the invariant region maintains a fixed offset from the starting position of the object, independent of subsequent derivations.
The shared area contains virtual base classes and then fluctuates in derivation and derivation order.
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