Whats the difference between member initializing and assignment while constructing?
First of all, be clear on what “member initializing” is. It is accomplished through a member initializer list. It is “spelled” by putting a colon and one or more constructor style initializers after the right parenthesis of the constructor: struct xyz { int i; xyz() : i(99) { } // Style A }; xyz x; will initialize x.i to 99. The issue on the table here is what’s the difference between that and doing this: struct abc { int i; abc() { i = 99; } // Style B }; Well, if the member is a const, then style B cannot possibly work: struct HasAConstMember { const int ci; HasAConstMember() { ci = 99; } // not possible }; since you cannot assign to a const. Similarly, if a member is a reference, it needs to be bound to something: struct HasARefMember { int &ri; HasARefMember() { ri = SomeInt; } // nope }; This does not bind SomeInt to ri (nor does it (re)bind ri to SomeInt) but instead assigns SomeInt to whatever ri is a reference to. But wait, ri is not a reference to anything here yet, and that’s
