How C++ accesses polymorphic objects through pointers or references
This article mainly explains how C++ accesses polymorphic objects through pointers or references, which interested friends may wish to have a look at. The method introduced in this paper is simple, fast and practical. Let the editor take you to learn how C++ accesses polymorphic objects through pointers or references.
Access polymorphic objects through pointers or references
Reason (reason)
If you have a class with a virtual function, you don't (in general) know which class provided the function to be used.
If a class has a virtual function, you usually don't know which (derived) class provides the function you are using.
Example (example) struct B {int a; virtual int f (); virtual ~ B () = default}
Struct D: B {int b; int f () override;}
Void use (BB)
{
D d
Bb2 = d; / / slice
Bb3 = b
}
Void use2 ()
{
D d
Use (d); / / slice
}
Both ds are sliced.
Both d (in the function) are cut off (because the derived class object assigns values to the base class object)
Exception (exception)
You can safely access a named polymorphic object in the scope of its definition, just don't slice it.
You can safely use the variable name in the scope where the polymorphic object is defined, as long as you are careful not to be cut off.
Void use3 ()
{
D d
D.F (); / / OK
}
See also (see)
A polymorphic class should suppress copying (polymorphic classes should suppress replication)
Enforcement
Flag all slicing. (Mark the operation of data cutoff)
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