Thread: MinGW doesn't value-initialize dynamic arrays of built-in type?

Can you please confirm this?

The output is undefined under the latest MinGW version.

Code:

int* arr = new int[5]();
cout << *arr << endl;

Bah!
Wrong forum. Sorry.

>>latest MinGW version<<

This is ambiguous.

>>Can you please confirm this?<<

With g++.exe (GCC) 3.4.5 (mingw special), yes; I wouldn't expect it to do otherwise.

Originally Posted by Tonto

Can I ask what those () do in that case?

They value-initialize the dynamic object. They behave much like a default constructor. For built-in types, they request the compiler to initialize the object as if it had been defined globally. An int gets initialized to 0, for instance.

try:
int* i = new int();
int* x = new int;

Originally Posted by Ken Fitlike

I wouldn't expect it to do otherwise.

Could you please elaborate Ken?

Originally Posted by Tonto

Why does it have this functionality, but does not allow an initializer or aggregate initialization (don't know the term?) like java

It allows an initializer if the object as that constructor defined. Obviously built-in types don't. That's why you can't initialize them with anything other than ().

But if on the other hand you are initializing a class, then you can use one of the constructors defined for that class. Take std::string for instance... or one of your user-defined classes.

Originally Posted by Tonto

Also, if they are initialized as they would be if they were globally, isn't that like static zeroed memory? For non-built in types, is it zeroed also?

For non-built in types, I replied above. It gets initialized according to the constructor definition. For built-in types, it depends on the type and, i'm pretty sure, on the compiler. On my implementation a bool gets initialized to 0 and a char to a space char.

My curiousity led me to this interesing post from a related thread.

[edit]http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20427

Well, in the end what matters essentially is that it seems this is compiler defined for arrays of built-in type. So, the best is to avoid it. Even though the way I'm reading ISO 14882 at 8.5 seems to give credit to my initial claim that the array should be zero initialized.

As for non arrays I think the norm is to zero initialize objects with this syntax. So I may rely on it.

Oh! Excellent source that edit Dave. Thanks!

That explains it.

Originally Posted by Mario F.

Could you please elaborate Ken?

Sorry, Mario, I skimmed your code and didn't notice the (); ironic given my comment about ambiguity. To be honest I wasn't aware of that feature; for what it's worth it is implemented in linux gcc (v3.3, anyway).

Yup, I was wrong on that particular case. The parenthesis need to be empty for array types.

However, needs to be said that any constructor that behaves like a default constructor will default-initialize.

Code:

class myClass {
   public:
      myClass(int val = 6, std::string &str = "Hello"): val_(val), str_(str) {}
   private:
      int val_;
      std::string str_;
};

// and on main()...
myClass = new myClass[5] ();  // all elements will be default-initialized according
                              // to de default constructor above.