Re: [webkit-dev] deleteOwnedPtr(T* ptr)

[Daebarkee Jung]

Thanks, all of you.
Now, everything is clear.

Daebark

On Thu, Nov 11, 2010 at 2:24 AM, Finnur Thorarinsson fin...@chromium.orgwrote:

 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 da...@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-destructor-calls

 http://connect.microsoft.com/VisualStudio/feedback/details/231177/delete-of-pointer-to-incomplete-class

 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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[webkit-dev] deleteOwnedPtr(T* ptr)

[Daebarkee Jung]

Hi,

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?

For error-fix, I changed it like the following:

template typename T inline void deleteOwnedPtr(T* ptr)
{
  if(sizeof(T)0)
delete ptr;
}

What could be the above code's mistake?


Thanks,

Daebark
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