Why does casting a CString to wchar_t* yield a temporary copy? What if we used some other type instead of CString?

Question

PVS studio found a potential defect which I am investigating; warning V623 http://www.viva64.com/en/d/0240/

However, not enough is explained to understand why the temporary copy is being made. If CString::operator wchar_t*() is defined like:

wchar_t* newbuf = new wchar_t[20];
// do things to put the current CString value in there
return newbuf;

Then there's a memory leak, but no pointer to a destroyed temporary. I see only one other possible implementation, which is to return an already existing wchar_t* pointer contained in the CString, which would not make a new temporary. Something like this:

return m_pContents;

So, two questions; where can I find the actual implementation for CString? And, what valid implementation of this function (on any selfmade type) could have the conversion operator return a pointer to a destroyed temporary? I just don't believe that Microsfoot would implement it like:

CString tempCopy(*this);
return tempCopy.m_pContents;

Answer 1

In your linked PVS studio code, you have a ternary operator taking a wchar_t * and a CString. Your problem is not with the conversion operator, but that the ternary is promoting the wchar_t * into a CString. You either need to assign the result to a new CString or make sure the ternary arguments are all the same type so that you get a reference back.