First of all, you should (must !) read this c++ faq regarding POD and aggregates. In your case, Foo is indeed a POD class and foo() is a value initialization :
To value-initialize an object of type
T means:
- if T is a class type (clause 9) with a user-declared constructor (12.1), then the default constructor
for T is called (and the initialization is ill-formed if T has no accessible default constructor);- if T is a non-union class type without a user-declared constructor, then every non-static data member and base-class component of T is value-initialized;
- if T is an array type, then each element is value-initialized;
- otherwise, the object is zero-initialized
So yes, foo will be zero-initialized. Note that if you removed this initialization from Bar constructor, foo would only be default-initialized :
If no initializer is specified for an
object, and the object is of (possibly
cv-qualified) non-POD class type (or
array thereof), the object shall be
default-initialized; if the object is
of const-qualified type, the
underlying class type shall have a
user-declared default constructor.
Otherwise, if no initializer is
specified for a nonstatic object, the
object and its subobjects, if any,
have an indeterminate initial
value;