Many classes have multiple constructors, and each constructor has its own member initialization list. If there are many data members and/or base classes, the existence of multiple initialization lists introduces undesirable repetition (in the lists) and boredom (in the programmers). In such cases, it’s not unreasonable to omit entries in the lists for data members where assignment works as well as true initialization, moving the assignments to a single (typically private) function that all the constructors call. This approach can be especially helpful if the true initial values for the data members are to be read from a file or looked up in a database. In general, however, true member initialization (via an initialization list) is preferable to pseudo-initialization via assignment.

One aspect of C++(www.cppentry.com) that isn’t fickle is the order in which an object’s data is initialized. This order is always the same: base classes are initialized before derived classes (see also Item 12), and within a class, data members are initialized in the order in which they are declared. In ABEntry, for example, theName will always be initialized first, theAddress second, thePhones third, and numTimesConsulted last. This is true even if they are listed in a different order on the member initialization list (something that’s unfortunately legal). To avoid reader confusion, as well as the possibility of some truly obscure behavioral bugs, always list members in the initialization list in the same order as they’re declared in the class.

Once you’ve taken care of explicitly initializing non-member objects of built-in types and you’ve ensured that your constructors initialize their base classes and data members using the member initialization list, there’s only one more thing to worry about. That thing is — take a deep breath — the order of initialization of non-local static objects defined in different translation units.