Default Initialization of Aggregates / Arrays

In VC2005 I have something like this:

Code:

---

struct t
{
        int ia[100];
        struct s { int a, b, c; } type;
        t() : ia(), type() { }
};

---

And I get the warning

Code:

---

warning C4351: new behavior: elements of array 'CWindow::_ia' will be default initialized

---

What is that new behavior thing? Should I not depend on this behavior? Is there a better way to default initialize members of the array? Also, am I guaranteed that all members of type will be default initialized?

I think this means that all the elements will be set by default to equal zero. Other than that, I've never seen that warning before.

That's standard behavior.

Arrays follow the same rules as other variables concerning default initialization.

However, to default initialize an array, give it one value. All other dimensions will be zero-initialized if it is an array of a built-in type.

Code:

---

int ia[100] = {0};  // initializes first element to 0, and zero-initializes all other elements

---

EDIT: Actually just payed attention to the warning. You compiler is bypassing the standard behavior by default initializing the array. That is non portable.

You can't have compound initialization in an initializer list, though.

I wasn't aware the syntax in the first post was even legal.

Code:

---

Arrays follow the same rules as other variables concerning default initialization.

However, to default initialize an array, give it one value. All other dimensions will be zero-initialized if it is an array of a built-in type.

       

Code:

       

---

int ia[100] = {0};  // initializes first element to 0, and zero-initializes all other elements

---

EDIT: Actually just payed attention to the warning. You compiler is bypassing the standard behavior by default initializing the array. That is non portable.

---

Yeah, as CornedBee said, I can't do such a thing in an initializer list and certainly not the body of a constructor. Any way to default initialize the array portably, or should I just memset or something? Will that syntax ever be adopted into the standard?

Being a struct you can always zero-initialize it at instantiation:

Code:

---

t object={0};

---

But that's not what you are asking. Other than memset of explicit assignment, I don't think you can.

Curiously enough it also zero-initialized the array on MinGW 3.4.5

Code:

---

class a {
    public:
        int arr[10];
        a():arr() {}
};

---

It compiles with no errors with -ansi and -pedantic on.

Stroustrup isn't totally clear on whether the initializer list can be empty, but with gcc this works for me:

Code:

---

int ia[100] = {};

---

Is this portable?

It's irrelevant to the problem. But yes, it's portable.

I also found the place where it kind of allows default-initializing arrays in class initializer lists.