@@ -6547,7 +6547,7 @@ That tends to work better than "cleverness" for non-specialists.
...
@@ -6547,7 +6547,7 @@ That tends to work better than "cleverness" for non-specialists.
The standard C++ mechanism to construct an instance of a type is to call its constructor. As specified in guideline [C.41](#Rc-complete): a constructor should create a fully initialized object. No additional initialization, such as by `memcpy`, should be required.
The standard C++ mechanism to construct an instance of a type is to call its constructor. As specified in guideline [C.41](#Rc-complete): a constructor should create a fully initialized object. No additional initialization, such as by `memcpy`, should be required.
A type will provide a copy constructor and/or copy assignment operator to appropriately make a copy of the class, preserving the type's invariants. Using memcpy to copy a non-trivially copyable type has undefined behavior. Frequently this results in slicing, or data corruption.
A type will provide a copy constructor and/or copy assignment operator to appropriately make a copy of the class, preserving the type's invariants. Using memcpy to copy a non-trivially copyable type has undefined behavior. Frequently this results in slicing, or data corruption.
##### Example, bad
##### Example, good
struct base
struct base
{
{
...
@@ -6560,16 +6560,28 @@ A type will provide a copy constructor and/or copy assignment operator to approp
...
@@ -6560,16 +6560,28 @@ A type will provide a copy constructor and/or copy assignment operator to approp
void update() override {}
void update() override {}
};
};
##### Example, bad
void init(derived& a)
void init(derived& a)
{
{
memset(&a, 0, sizeof(derived));
memset(&a, 0, sizeof(derived));
}
}
This is type-unsafe and overwrites the vtable.
##### Example, bad
void copy(derived& a, derived& b)
void copy(derived& a, derived& b)
{
{
memcpy(&a, &b, sizeof(derived));
memcpy(&a, &b, sizeof(derived));
}
}
This is also type-unsafe and overwrites the vtable.
##### Enforcement
- Flag passing a non-trivially-copyable type to `memset` or `memcpy`.
## <a name="SS-containers"></a>C.con: Containers and other resource handles
## <a name="SS-containers"></a>C.con: Containers and other resource handles