# C++ named requirements: TriviallyCopyable (since C++11)

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Note: the standard doesn't define a named requirement with this name. This is a type category defined by the core language. It is included here as a named requirement only for consistency.

### Requirements

The following types are collectively called trivially copyable types:

- scalar types
- trivially copyable class types
- arrays of such types
- cv-qualified versions of these types

### Notes

In general, for any trivially copyable type `T` and an object `obj1` of `T`, the underlying bytes of `obj1` can be copied into an array of char, or unsigned char, or `std::byte` (since C++17) or into `obj2`, a distinct object of `T`. Neither `obj1` nor `obj2` may be a potentially-overlapping subobject.

If the underlying bytes of `obj1` are copied into such an array, and then the resulting content is copied back into `obj1`, `obj1` will hold its original value. If the underlying bytes of `obj1` are copied into `obj2`, `obj2` will hold `obj1`'s value.

Underlying bytes can be copied by std::memcpy or std::memmove, as long as no living volatile object is accessed.

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
CWG 1734 | C++11 | C++03 POD with deleted non-trivial assignment was not trivial | deleted ctors/operators allowed
CWG 2094 | C++11 | Volatile scalar types are not trivially copyable (CWG 1746) | made trivially copyable

### See also

is_trivially_copyable (C++11) | checks if a type is trivially copyable (class template)

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