Double delete in initializer_list vs 2013

Question

Today in run into a memory problem in my project, with a class using c++ 11 initializer_list. The system signals a memory problem: \"Expression _BLOCK_TYPE_IS_VALID(pHead->n

Answer 1

The initializer_list behavior is buggy. In its destructor it calls a vector delete (a delete[]) of the entire range and then deletes the first entry in the array again. This behavior is not part of the initializer_list class and looks like a compiler bug. initializer_list doesn't have a destructor and doesn't allocate the array used for the list. It just looks like a wrapper for a C array.

As for using the extra copy you see, it's caused by the vector resizing from during its initialization. Here's your flow:

Init 00B7FAE8       // construct "foo"
Init 00B7FBE8       // construct "bar"
Copy 00E108A0       // copy "foo" to vector (capacity=1)
Copy 00E10AE8 (?????) // copy the above object to the resized vector (capacity = 2)
Deleting b 00E108A0   // delete the smaller vector buffer
Copy 00E10BE8         // copy "bar" from initialization_list to vector

Deleting b 00B7FBE8   // delete initialization_list in reverse order. this is "bar"
Deleting b 00B7FAE8   // last to delete. this is "foo"

Deleting b 00B7FAE8  (bug)

// later C::bs is destroyed

What you can see here is the initializing a vector via push_back is quite slow due to copying. This would be happen even if you've used the more elegant way:

C(initializer_list<B> bb) : bs(bb) {}

A faster (no extra copies) method is:

C(initializer_list<B> bb) {
    bs.reserve(bb.size());
    bs.insert(bs.end(), bb.begin(), bb.end());
}