POD type

What is POD type:A type that consists of nothing but Plain Old Data.A POD type is a C++ type that has an equivalent in C, and that uses the same rules as C uses for initialization, copying, layout, and addressing.As an example, the C declaration struct Fred x; does not initialize the members of the Fred variable x. To make this same behavior happen in C++, Fred would need to not have any constructors. Similarly to make the C++ version of copying the same as the C version, the C++ Fred must not have overloaded the assignment operator. To make sure the other rules match, the C++ version must not have virtual functions, base classes, non-static members that are private or protected, or a destructor. It can, however, have static data members, static member functions, and non-static non-virtual member functions.The actual definition of a POD type is recursive and gets a little gnarly. Here's a slightly simplified definition of POD: a POD type's non-static data members must be public and can be of any of these types: bool, any numeric type including the various char variants, any enumeration type, any data-pointer type (that is, any type convertible to void*), any pointer-to-function type, or any POD type, including arrays of any of these. Note: data-pointers and pointers-to-function are okay, but pointers-to-member are not. Also note that references are not allowed. In addition, a POD type can't have constructors, virtual functions, base classes, or an overloaded assignment operator.A POD is a type (including classes) where the C++ compiler guarantees that there will be no "magic" going on in the structure: for example hidden pointers to vtables, offsets that get applied to the address when it is cast to other types (at least if the target's POD too), constructors, or destructors. Roughly speaking, a type is a POD when the only things in it are built-in types and combinations of them. The result is something that "acts like" a C type.Less informally:int, char, wchar_t, bool, float, double are PODs, as are long/short and signed/unsigned versions of them.pointers (including pointer-to-function and pointer-to-member) are PODs,enums are PODsa const or volatile POD is a POD.a class, struct or union of PODs is a POD provided that all members are public, and it has no base class and no constructors, destructors, or virtual methods. Static members don't stop something being a POD under this rule.Wikipedia is wrong to say that a POD cannot have members of type pointer-to-member. Or rather, it's correct for the C++98 wording, but TC1 made explicit that pointers-to-member are POD.Here's what the C++ standard says:3.9(10): "Arithmetic types (3.9.1), enumeration types, pointer types, and pointer to member types (3.9.2) and cv-qualified versions of these types (3.9.3) are collectively caller scalar types. Scalar types, POD-struct types, POD-union types (clause 9), arrays of such types and cv-qualified versions of these types(3.9.3) are collectively called POD types"3.9(4): "A POD-struct is an aggregate class that has no non-static data members of type non-POD-struct, non-POD-union (or array of such types) or reference, and has no user-define copy operator and no user-defined destructor. Similarly a POD-union is an aggregate union that has no non-static data members of type non-POD-struct, non-POD-union (or array of such types) or reference, and has no user-define copy operator and no user-defined destructor.8.5.1(1): "An aggregate is an array or class (clause 9) with no user-declared constructors (12.1), no private or protected non-static data members (clause 11), no base classes (clause 10) and no virtual functions (10.3)."