Take an ordinary struct (or class) with Plain Old Data types and objects as members. Note that there is no default constructor defined.
struct Foo
{
int x;
int y;
double z;
string str;
};
Now if I declare an instance f on the stack and attempt to print its contents:
{
Foo f;
std::cout << f.x << " " << f.y << " " << f.z << f.str << std::endl;
}
The result is garbage data printed for x, y, and z. And the string is default initialized to be empty. As expected.
If I create an instance of a shared_ptr<Foo>
using make_shared
and print:
{
shared_ptr<Foo> spFoo = make_shared<Foo>();
cout << spFoo->x << " " << spFoo->y << " " << spFoo->z << spFoo->str << endl;
}
Then, x, y, and z are all 0
. Which makes it appear that shared_ptr
performs a default initialization (zero init) on each member after the object instance is constructed. At least that's what I observe with Visual Studio's compiler.
Is this standard for C++? Or would it be necessary to have an explicit constructor or explicit ={}
statement after instantiation to guarantee zero-init behavior across all compilers?