问题
If I've overloaded operator+ and operator= do I still need to overload operator+= for something like this to work:
MyClass mc1, mc2;
mc1 += mc2;
回答1:
operator+= is not a composite of + and =, therefore you do need to overload it explicitly, since compiler do not know to build puzzles for you. but still you do able to benefit from already defined/overloaded operators, by using them inside operator+=.
回答2:
Yes, you need to define that as well.
A common trick however, is to define operator+=, and then implement operator+ in terms of it, something like this:
MyClass operator+ (MyClass lhs, const MyClass& rhs){
return lhs += rhs;
}
If you do it the other way around (use + to implement +=), you get an unnecessary copy operation in the += operator which may be a problem i performance-sensitive code.
回答3:
Yes, you do.
回答4:
If the real question here is, "I don't want to write a load of repetitive operators, please tell me how to avoid it", then the answer may be:
http://www.boost.org/doc/libs/1_38_0/libs/utility/operators.htm
The syntax looks a little fiddly, though. As I've never used it myself, I can't reassure you that it's simple really.
来源：https://stackoverflow.com/questions/1092331/overloading-in-c