This rule is part of MISRA C++:2023.
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Rule 8.2.11 - An argument passed via ellipsis shall have an appropriate type
Category: Required
Analysis: Decidable, Single Translation Unit
Amplification
The following types are not appropriate:
-
class types with virtual member functions;
-
class types having non-trivial copy or move operations;
-
class types having a non-trivial destructor.
This rule does not apply to unevaluated contexts.
Rationale
Passing arguments of some class types via an ellipses parameter is only conditionally-supported with
implementation-defined behaviour.
Default argument promotions are applied to ellipsis parameters, which may lead to the type that is passed to the function differing from the type
that would be passed to a normal function parameter or when passed as a parameter pack.
Note: passing arguments to a parameter pack is not passing via ellipsis.
Example
struct A
{
int i { 42 };
virtual ~A() = default;
};
void f()
{
std::printf ( "hello %d", A{} ); // Non-compliant
}
The following example uses overload resolution and type deduction; it does not pass an argument via ellipsis at run-time:
struct two { char x[2]; };
two test( int );
char test( ... );
template< typename T >
constexpr bool isIntCompatible( T x )
{
if constexpr ( sizeof( test( x ) ) == 1 ) // Compliant - unevaluated context
{
return false; // Overload resolution -> test( ... )
}
else
{
return true; // Overload resolution -> test( int )
}
}
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