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This article mainly explains "how C++ uses dynamic_cast". Interested friends may wish to have a look at it. The method introduced in this paper is simple, fast and practical. Let the editor take you to learn "how C++ uses dynamic_cast".

C.148: when using dynamic_cast for pointer type conversion, the target class cannot be found as a valid option

Reason (reason)

The dynamic_cast transformation allows you to check whether the pointer points to a polymorphic object that contains a given class in its inheritance structure. Since the result of a failed conversion simply returns a null value, this result can be checked at execution time. This feature allows you to choose different paths based on the results. Unlike C.147, the failure there is an error and should not be used for conditional execution.

Example (sample)

The following example describes the add-on function of Shape_owner, which accepts ownership of the constructed Shape object. Objects are also added to the views container sequentially according to their geometric properties. In this example, the drawing does not inherit from geometric properties. Only its subclasses do so.

Void add (Shape* const item)

{

/ / Ownership is always taken

Owned_shapes.emplace_back (item)

/ / Check the Geometric_attributes and add the shape to none/one/some/all of the views

If (auto even = dynamic_cast (item))

{

View_of_evens.emplace_back (even)

}

If (auto trisym = dynamic_cast (item))

{

View_of_trisyms.emplace_back (trisym)

}

}

Notes (Note)

Failure to find the desired class causes dynamic_cast to return a null value, while dereferencing a null pointer causes undefined behavior. Therefore, you should always assume that the result of the dynamic_cast may be null and check.

Enforcement (implementation recommendations)

(complex) if no null judgment is made on the result pointer after the execution of the dynamic_cast, an alarm is given to the code that uses the pointer.

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