CS253: Software Development with C++
Spring 2018
Increment Methods
If you’re writing a class that is numeric or pointery, then it needs:
++obj)
obj++)
--obj)
obj--)
None of these come for free. You have to write them all.
Preincrement is easy:
Whatever &operator++() { // No argument means preincrement
// Do what is needed to change the object
// which might be *this += 1;
return *this;
}
Fast & efficient—no copying is required.
Postincrement is harder, but can be the same for nearly all classes:
Whatever operator++(int) { // Dummy int arg means postincrement
const auto save = *this;
++*this; // Call the preincrement method
return save;
}
Less efficient—need to make a copy, and return by value.
Pre-/post-decrement is essentially the same. Get pre-/post-increment working, and then (I can’t believe that I’m saying this) use copy & paste.
operator++ should use operator+= to accomplish
the increment. Less duplication of information—good!
