Default constructor in template class with attribute of unknown type

Question

I need a default constructor with no argument. How can I initialize attribute a which is of unknown type to me.

template <typename Type>
class Foo
{
public:
    Foo() : a(), b(0) {}  <---- Here is the confusion

private:
    Type a;
    int b;
};

Edit : Answer has been given in comments below, but there is still something I don't understand. If I have :

typedef enum {AB, CD} EnumType

template <typename Type>
class Foo
{
public:
    Foo() {}  // <---- "Member 'b' was no initialized in this constructor"

private:
    Type a;
    EnumType b;
};

my compiler gives me this warning : Member 'b' was no initialized in this constructor. Why is it giving me this warning for b which is an enum and not for a ?

Answer 1

How can I initialize attribute a which is of unknown type to me.

Your solution is correct. Per Paragraph 8.5/11 of the C++11 Standard:

An object whose initializer is an empty set of parentheses, i.e., (), shall be value-initialized. [...]

Then, Paragraph 8.5/8:

To value-initialize an object of type T means:

— if T is a (possibly cv-qualified) class type (Clause 9) with either no default constructor (12.1) or a default constructor that is user-provided or deleted, then the object is default-initialized;

— if T is a (possibly cv-qualified) non-union class type without a user-provided or deleted default constructor, then the object is zero-initialized and, if T has a non-trivial default constructor, default-initialized;

— if T is an array type, then each element is value-initialized;

— otherwise, the object is zero-initialized.

Finally,

Why is it giving me this warning for b which is an enum and not for a ?

That is probably because you specify a template argument for Type which is a UDT (user-defined type) which can be default-constructed. If this is not the case, then I would expect the compiler to also warn you about a not being initialized in the constructor. Notice, however, that the compiler is not required to issue any such warning.