Thanks, all of you. Now, everything is clear. Daebark On Thu, Nov 11, 2010 at 2:24 AM, Finnur Thorarinsson <finnur@chromium.org>wrote:
Umm... shouldn't this behavior be commented so that people are not left wondering why it fails and trying to "fix" it?
On Wed, Nov 10, 2010 at 16:04, Darin Adler <darin@apple.com> wrote:
On Nov 10, 2010, at 2:33 PM, Daebarkee Jung wrote:
I found that the following lines made errors: // OwnPtrCommon.h template <typename T> inline void deleteOwnedPtr(T* ptr) { typedef char known[sizeof(T) ? 1 : -1]; if (sizeof(known)) delete ptr; }
I am very curious about why the author wrote like the above. What could be the author's intention?
The code is to prevent issues like the ones described on these websites:
http://stackoverflow.com/questions/1767679/incomplete-type-memory-leaks
http://bytes.com/topic/c/answers/611877-gcc-class-forward-declarations-destr...
http://connect.microsoft.com/VisualStudio/feedback/details/231177/delete-of-...
If we delete a pointer and the object has incomplete type, we get undefined behavior. Instead this code causes compilation to fail if the object has incomplete type. The use of a negative number for the size of an array is a way to guarantee we get a compilation error.
Your alternate version might also work; I’m not sure.
-- Darin
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