rspec/rules/S5302/cfamily/rule.adoc

== Why is this an issue?

Casting from a virtual base to a derived class, using any means other than dynamic_cast has undefined behaviour. The behaviour for dynamic_cast is defined.


Note: As of {cpp}17, the program is considered as ill-formed and an error is reported.

Most compilers emit an error for previous versions of {cpp} as well.


=== Noncompliant code example

[source,cpp]
----
class B { ... };
class D: public virtual B { ... };
D d;
B *pB = &d;

D *pD1 = ( D * ) pB; // Noncompliant - undefined behaviour
D *pD2 = static_cast<D*>(pB); // Noncompliant - undefined behaviour
----


=== Compliant solution

[source,cpp]
----
class B { ... };
class D: public virtual B { ... };
D d;
B *pB = &d;

D *pD1 = dynamic_cast<D*>(pB); // Compliant, but pD2 may be NULL
D & D2 = dynamic_cast<D&>(*pB); // Compliant, but may throw an exception
----


== Resources

* MISRA {cpp}:2008, 5-2-2 - A pointer to a virtual base class shall only be cast to a pointer to a derived class by means of dynamic_cast.


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== Comments And Links
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