Like the title says. If two or more keys in a map that uses any non-primitive key become NULL for any reason, then it is not possible to Remove(NULL) these elements from the map. The workaround is to use RemoveElement(n) instead.
As to why this can be a problem with unexpected consequences that will even lead to a CTD, see https://feedback.bistudio.com/T163613
Minimal example:
class MyTestClass
{
}
map<MyTestClass, bool> test();
MyTestClass c1();
MyTestClass c2();
test.Insert(c1, true);
test.Insert(c2, false);
delete c1;
delete c2; //! Now we have two NULL keys in the map
MyTestClass k;
bool v;
int n;
Print(test.ToString() + " count " + test.Count());
for (n = 0; n < test.Count(); n++)
{
v = test.GetElement(n);
if (v)
{
k = test.GetKey(n);
Print("Removing element with key " + k);
test.Remove(k); //! This will fail because there are two NULL keys in the map
}
}
Print(test.ToString() + " count " + test.Count());
for (n = 0; n < test.Count(); n++)
{
k = test.GetKey(n);
v = test.GetElement(n);
Print("Element " + n + " key " + k + " value " + v);
}
for (n = 0; n < test.Count(); n++)
{
v = test.GetElement(n);
if (v)
{
k = test.GetKey(n);
Print("Removing element " + n);
test.RemoveElement(n); //! This will work
}
}
Print(test.ToString() + " count " + test.Count());Will print the following:
SCRIPT : map<MyTestClass,bool><acf3fc00> count 2 SCRIPT : Removing element with key NULL SCRIPT : map<MyTestClass,bool><acf3fc00> count 2 SCRIPT : Element 0 key NULL value true SCRIPT : Element 1 key NULL value false SCRIPT : Removing element 0 SCRIPT : map<MyTestClass,bool><acf3fc00> count 1
I was half wrong actually, literally. There is only one NULL pointer key needed in the map for it to be not removable with map.Remove(NULL), as that would try to remove literal NULL from the map, not the key that originally pointed to an instance, but now points to NULL. Effect stays the same though.