C++ destructor format

 void arrayLis开发者_运维百科t<T>::erase(int theIndex) {
            // valid index, shift elements with higher index
            copy(element + theIndex + 1, element + listSize, element + theIndex);

            element[--listSize].~T(); // invoke destructor 
        }

The code element[--listSize].~T() looks strange. It is used to delete the dynamically allocated element. Does any know why we can use this syntax?

EDIT

The problem is solved.

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That would be useful if you have allocated memory for elements[i] using placement new operator. See What is "placement new" and why would I use it? for details.

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Does any know why we can use this syntax?

We use it to invoke the destructor on an object allocated with placement new, generally. See also this page.

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Explicitly calling the destructor is useful in cases where you want to properly destruct the object, but not deallocate it's memory by using delete (or delete[]) directly, such as inside some custom memory manager. It should not be used very often though.

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The code element[--listSize].~T() looks strange. It is used to delete the dynamically allocated element. Does any know why we can use this syntax?

It is used to destroy that object; this is probably what you meant, but "delete" has other meanings in C++. You need to do this if you construct each item manually.

You can use this syntax because it is specifically allowed by the language. The opposite of a manual destructor call is placement new.

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Yes you are correct they are explicitly invoking the destructor ...

However you can fix all of the problems with this implementation by throwing it out and using std::vector or std::list instead!