Rule Definition
The use of unions to access an object in different ways may result in the data being misinterpreted. Therefore, this rule prohibits the use of unions for any purpose. It is recognized nonetheless that there are situations in which the careful use of unions is desirable in constructing an efficient implementation. In such situations, deviations to this rule are considered acceptable provided that all relevant implementation-defined behaviour is documented. This might be achieved in practice by referencing the implementation section of the compiler manuals from the design documentation.

Remediation
In case it is desired to use Unions it is strongly advised to create a deviation.

Violation Code Sample

namespace NS1
{
// Compliant - no union
}
namespace NS2
{
union U1 // Non-compliant – union
{
int32_t i;
float32_t j;
};
}

MISRA C++, 2008, 9-5-1: Unions shall not be used AUTOSAR C++, 2014, M9-5-1: Unions shall not be used