用語メモ

3.9 Types [basic.types]

2 For any object (other than a base-class subobject) of POD type T, whether or not the object holds a valid value of type T, the underlying bytes (1.7) making up the object can be copied into an array of char or unsigned char.36) If the content of the array of char or unsigned char is copied back into the object, the object shall subsequently hold its original value. [Example:
#define N sizeof(T)
char buf[N];
T obj; // obj initialized to its original value
memcpy(buf, &obj, N); // between these two calls to memcpy,
// obj might be modified
memcpy(&obj, buf, N); // at this point, each subobject of obj of scalar type
// holds its original value
—end example]
3.9 Types [basic.types]

3 For any POD type T, if two pointers to T point to distinct T objects obj1 and obj2, where neither obj1 nor obj2 is a base-class subobject, if the value of obj1 is copied into obj2, using the memcpy library function, obj2 shall subsequently hold the same value as obj1. [Example:
T* t1p;
T* t2p;
// provided that t2p points to an initialized object ...
memcpy(t1p, t2p, sizeof(T)); // at this point, every subobject of POD type in *t1p contains
// the same value as the corresponding subobject in *t2p
—end example]
3.9 Types [basic.types]

10 Arithmetic types (3.9.1), enumeration types, pointer types, and pointer to member types (3.9.2), and cvqualified versions of these types (3.9.3) are collectively called 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.
8.5.1 Aggregates [dcl.init.aggr]

1 An aggregate is an array or a 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).
9 Classes [class]

4 A structure is a class defined with the class-key struct; its members and base classes (clause 10) are public by default (clause 11). A union is a class defined with the class-key union; its members are public by default and it holds only one data member at a time (9.5). [Note: aggregates of class type are described in 8.5.1. ] 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-defined copy assignment 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 userdefined copy assignment operator and no user-defined destructor. A POD class is a class that is either a POD-struct or a POD-union.

もともとはunderlying bytesの単純なコピーがオブジェクトのコピーと同義となる十分条件を正確に知りたかっただけとゆ〜・・・.今までPOD, POD-struct, aggregatesの定義を曖昧に覚えてたんだよにゃ〜.これでぱ〜ぺき.ちぃ覚えた.