but I can’t see anything in the standard that therefore allows me to reinterpret_cast between them, even though that seems like the reasonable interpretation of “value representation”. Is this technically allowed by the standard? No. The standard is clear (see [basic.lval] p10) about which types can be aliased, and layout-compatible types are not included. If … Read more
In your example that you provided str will not be destructed. The standard states in [class.union]/2 A union can have member functions (including constructors and destructors), but not virtual (10.3) functions. A union shall not have base classes. A union shall not be used as a base class. If a union contains a non-static data … Read more
The answer to this question doesn’t come from the standard but rather from the Itanium ABI (which is why gcc and clang have one behavior but msvc does something else). That ABI defines a layout, the relevant parts of which for the purposes of this question are: For purposes internal to the specification, we also … Read more
You are allowed to cast a standard layout class object address to a pointer to its first member and back by one of the later paragraphs, which is also often done in C: struct A { int x; }; A a; // “px” is guaranteed to point to a.x int *px = (int*) &a; // … Read more
How to read: This article is rather long. If you want to know about both aggregates and PODs (Plain Old Data) take time and read it. If you are interested just in aggregates, read only the first part. If you are interested only in PODs then you must first read the definition, implications, and examples … Read more