constexpr std::size_t N = sizeof(T); char buf[N]; T obj; // obj initialized to its original value std::memcpy(buf, &obj, N); // between these two calls to std::memcpy, obj might be modified std::memcpy(&obj, buf, N); // at this point, each subobject of obj of scalar type holds its original value— end example
T* t1p; T* t2p; // provided that t2p points to an initialized object ... std::memcpy(t1p, t2p, sizeof(T)); // at this point, every subobject of trivially copyable type in *t1p contains // the same value as the corresponding subobject in *t2p— end example
class X; // X is an incomplete type extern X* xp; // xp is a pointer to an incomplete type extern int arr[]; // the type of arr is incomplete typedef int UNKA[]; // UNKA is an incomplete type UNKA* arrp; // arrp is a pointer to an incomplete type UNKA** arrpp; void foo() { xp++; // error: X is incomplete arrp++; // error: incomplete type arrpp++; // OK: sizeof UNKA* is known } struct X { int i; }; // now X is a complete type int arr[10]; // now the type of arr is complete X x; void bar() { xp = &x; // OK; type is “pointer to X” arrp = &arr; // error: different types xp++; // OK: X is complete arrp++; // error: UNKA can't be completed }— end example
Type | Minimum width N |
signed char | 8 |
short | 16 |
int | 16 |
long | 32 |
long long | 64 |
no cv-qualifier | < | const |
no cv-qualifier | < | volatile |
no cv-qualifier | < | const volatile |
const | < | const volatile |
volatile | < | const volatile |