面向对象程序设计语言C++第2版 教学课件 作者 陈文宇 面向对象程序设计语言C++ - 第5章 运算符重载.pptVIP

第五章 引论 5.1 重载运算符 5.1.3一元和二元运算符 (2)友元函数重载运算符 type operator @(Class_Name obj1,Class_Name obj2) { … } 显式调用方式： operator @(obj1,obj2) 隐式调用方式： obj1 @ obj2 （例5-7/8） * 第五章 引论 5.1 重载运算符 5.1.3一元和二元运算符 3．运算符重载为成员函数和友元函数的选择建议 * non-member All other binary operators member += –= /= *= ^= = |= %= = = must be member = () [] – –* member All unary operators Recommended Use Operator 第五章 引论 5.1 重载运算符 5.1.3一元和二元运算符 1）As with any function argument, if you only need to read from the argument and not change it, default to passing it as a const reference. Ordinary arithmetic operations (like + and –, etc.) and Booleans will not change their arguments, so pass by const reference is predominantly what you’ll use. When the function is a class member, this translates to making it a const member function. Only with the operator-assignments (like +=) and the operator=, which change the left-hand argument, is the left argument not a constant, but it’s still passed in as an address because it will be changed. * 第五章 引论 5.1 重载运算符 5.1.3一元和二元运算符 2）The type of return value you should select depends on the expected meaning of the operator. (Again, you can do anything you want with the arguments and return values.) If the effect of the operator is to produce a new value, you will need to generate a new object as the return value. This object is returned by value as a const, so the result cannot be modified as an lvalue. * 第五章 引论 5.1 重载运算符 5.1.3一元和二元运算符 3）All the assignment operators modify the lvalue. To allow the result of the assignment to be used in chained expressions, like a=b=c, it’s expected that you will return a reference to that same lvalue that was just modified. But should this reference be a const or nonconst? Although you read a=b=c from left to right, the compiler parses it from right to left, so you’re not forced to return a nonconst to support assignment chaining. However, people do sometimes expect to be able to perform an operation on the thing that was just assigned to, s