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Classes and Resource Ownership · 3:38
Copying: Shallow vs Deep
The default copy of a class copies its members one by one, so two Vectors end up sharing one heap block: a write through one shows up in the other, and at the end of the scope the block is deleted twice and the program aborts. We fix it with a copy constructor and a copy assignment that duplicate the block, allocate before deleting so a failure leaves the object untouched, and finish with the copy-and-swap idiom.
You will learn
- Explain why the default memberwise copy is wrong for a class that owns a resource
- Recognise a double free and how it shows up on a real machine
- Write a deep-copy constructor and a copy assignment that gives the strong guarantee
- Implement copy assignment with the copy-and-swap idiom