If I have a map, and insert an element like so:
map::<string, MyCustomClass> myMap;
MyCustomClass test1;
MyCustomClass test2;
myMap["hi"] = test1; // adds an element with a key
myMap["hi"] = test2; // replaces
When test2 replaces test1, does test1 get released from memory?
The copy of test1 that is stored in the map is destructed, yes. The orignal test1 you made a copy of remains unchanged.
Actually, no it's not. The second myMap["hi"] returns a reference to the MyCustomClass object constructed by the first myMap["hi"] call. That reference is used to call the assignment operator. It won't be destroyed until its node is erased, either explicitly through erase() or implicitly such as through the destruction of the map.The copy of test1 that is stored in the map is destructed, yes.
Correct, I should have realized that if I spent just a few seconds thinking about it; "replaces" as OP wrote in his comment is more accurate. But the key thing, I believe, is what happens to test1: nothing.
Once I replace test2 with test1, has this caused a memory leak? I'm wondering if I should be safe, and use insert(), or just check if the key already in use with find(), erase() if valid, then insert() or construct using "[] =" (bracket assignment).
Since you didn't allocate them using new there won't be a memory leak
Ok, that's good to hear. I thought "new" was used internally, and wanted to make sure since the data is copied into meaning more data is allocated upon performing that operation.
You can get leaks if MyCustomClass doesn't follow the rule of three, or simply doesn't have a destructor when it needs one.
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