C++ object created with new, destroyed with free(); How bad is this?

Question

I am working on modifying a relatively large C++ program, where unfortunately it is not always clear whether someone before me used C or C++ syntax (this is in the electrical engineering department at a university, and we EEs are always tempted to use C for everything, and unfortunately in this case, people can actually get away with it).

However, if someone creates an object:

Packet* thePacket = new Packet();

Does it matter whether it is destroyed with delete thePacket; or free(thePacket); ?

I realize that delete calls the destructor while free() does not, but Packet does not have a destructor. I am having a terrible time stuck in a memory management swamp here and I'm thinking this may be one of the many problems.

Answer 1

Yes it does matter.

For memory obtained using new you must use delete.

For memory obtained using malloc you must use free.

new and malloc may use different data structures internally to keep track of what and where it has allocated memory. So in order to free memory, you have to call that corresponding function that knows about those data structures. It is however generally a bad idea to mix these two types of memory allocation in a piece of code.