This is a draft version of a MISRA C++ 202x rule proposed for public review.
MISRA Rule 21.6.5
Category: Required
Analysis Type: Decidable,Single Translation Unit
Rationale
An incomplete class type is a forward declared class type for which the compiler has not yet seen a complete definition.
Deleting a pointer to an incomplete class type results in undefined behaviour when the complete class has a non-trivial
destructor or a deallocation function.
This rule prohibits deletion of a pointer to an incomplete class type even when it is a trivially destructible class without a deallocation
function. This restriction defends against a non-trivial destructor or a deallocation function being added during development.
Example
The following examples violate MISRA C++ 2023 Rule 21.6.2 (Dynamic memory shall be managed automatically).
class Bad
{
class Impl;
Impl * pImpl;
public:
~Bad()
{
delete pImpl; // Non-compliant - at the point of deletion, pImpl points
// to an object of incomplete class type.
}
};
// Header file
class Good
{
class Impl;
Impl * pImpl;
public:
~Good();
};
// Implementation file
class Good::Impl
{
};
// Good::Impl is a complete type now
Good::~Good()
{
delete pImpl; // Compliant - at the point of deletion, pImpl points to
// a complete class type.
}
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