Do classes with uninitialized pointers have undefined behavior?

Question

class someClass
{
public:
    int* ptr2Int;
};

Is this a valid class (yes it compiles)? Provided one assigns a value to ptr2Int before dereferencing it, is the class guaranteed to work as one would expect?

Answer 1

An uninitialized pointer inside a class is in no way different from a standalone uninitailized pointer. As long as you are not using the pointer in any dangerous way, you are fine.

Keep in mind though that "dangerous ways" of using an uninitialized pointer include a mere attempt to read its value (no dereference necessary). The implicit compiler-provided copy-constructor and copy-assignment operators present in your class might perform such an attempt if you use these implicit member functions before the pointer gets assigned a valid value.

Actually, if I'm not mistaken, this issue was a matter of some discussion at the level of the standardization committee. Are the implicitly generated member functions allowed to trip over trap representations possibly present in the non-initialized members of the class? I don't remember what was the verdict. (Or maybe I saw that discussion in the context of C99?)