Token Leaks – Implementation

To implement token leak detection, a token pointer list was added to the Token class as a static member and a token list element pointer was added as a regular member.  The new and delete operators were overloaded in the Token class to be able to maintain this token list.

The overloaded new operator function first allocates an array of bytes for the size argument, which is type cast to a Token pointer. The token pointer is appended to the static token pointer list and the element pointer returned from the list append function is put into the element pointer member of the token. The value of the token pointer is returned.

The overloaded delete operator function type casts the void pointer to a token pointer. If the element pointer is NULL, then this token has already been deleted. Otherwise the element pointer in the token is used to remove the token pointer from the token pointer list. The element pointer of the token is set to NULL to indicate that it has been deleted (to detect multiple deletes of the same token). The memory used by the token is then deleted.

This additional error that can occur when a token being deleted more than once. To also catch these errors, when a token is being deleted, if its element pointer is NULL, then a copy of the token will be added to a new delete list, which will be a list of tokens. A copy of the token needs to be made because the memory has already been deleted and could be reused by another allocation. It's also possible that the memory may have already been reused and the token copy will be garbage, but at least it will be known there is an extra delete somewhere.

Finally, the test code was modified to output any tokens that have not been deleted once the RPN output list has been output and cleaned up (all of its tokens deleted). The tokens in the delete list are also output. Once the code was working and running, many token leaks were found (in six of the Translator tests), and Translator test 12 (more error tests) was crashing. Time to fix some problems...