C++ New
struct A { int m; }; // POD
struct B { ~B(); int m; }; // non-POD, compiler generated default ctor
struct C { C() : m() {}; ~C(); int m; }; // non-POD, default-initialising m
In a C++03 conformant compiler, things should work like so:
new A- indeterminate valuenew A()- value-initialize A, which is zero-initialization since it’s a POD.new B- default-initializes (leaves B::m uninitialized)new B()- value-initializes B which zero-initializes all fields since its default ctor is compiler generated as opposed to user-defined.new C- default-initializes C, which calls the default ctor.new C()- value-initializes C, which calls the default ctor.
new Thing(); is explicit that you want a constructor called whereas new Thing; is taken to imply you don’t mind if the constructor isn’t called.new Thing(); is explicit that you want a constructor called whereas new Thing; is taken to imply you don’t mind if the constructor isn’t called.
If used on a struct/class with a user-defined constructor, there is no difference. If called on a trivial struct/class (e.g. struct Thing { int i; };) then new Thing; is like malloc(sizeof(Thing)); whereas new Thing(); is like calloc(sizeof(Thing)); - it gets zero initialized.