C++ 重载 operator== 抱怨“必须只采用一个参数”
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overloading operator== complaining of 'must take exactly one argument'
提问by chlong
I am trying to overload the operator==, but the compiler is throwing the following error:
我试图重载operator==，但编译器抛出以下错误：
‘bool Rationalnumber::operator==(Rationalnumber, Rationalnumber)' must take exactly one argument
My short piece of code is as follows:
我的一小段代码如下：
bool Rationalnumber::operator==(Rationalnumber l, Rationalnumber r) {
return l.numerator() * r.denominator() == l.denominator() * r.numerator();
}
Declaration:
宣言：
bool operator==( Rationalnumber l, Rationalnumber r );
Does anyone have any ideas why it's throwing the error?
有没有人知道为什么会抛出错误？
回答by juanchopanza
If operator==is a non static data member, is should take only one parameter, as the comparison will be to the implicit thisparameter:
如果operator==是非静态数据成员，则应该只带一个参数，因为比较将与隐式this参数进行比较：
class Foo {
bool operator==(const Foo& rhs) const { return true;}
};
If you want to use a free operator (i.e. not a member of a class), then you can specify two arguments:
如果要使用自由运算符（即不是类的成员），则可以指定两个参数：
class Bar { };
bool operator==(const Bar& lhs, const Bar& rhs) { return true;}
回答by Plexico
As a memberoperator overload it should only take one argument, the other being this.
作为成员运算符重载，它应该只接受一个参数，另一个是this.
class Foo
{
int a;
public:
bool operator==(const Foo & foo);
};
//...
bool Foo::operator==(const Foo & foo)
{
return a == foo.a;
}
回答by tim-oleksii
You should remove your operator== from a RationalNumber to somewhere else. As it is declared inside a class it is considered that 'this' is the first argument. From semantics it is seen that you offer 3 arguments to a compiler.
您应该将您的 operator== 从 RationalNumber 删除到其他地方。由于它是在类中声明的，因此认为“this”是第一个参数。从语义上可以看出，您向编译器提供了 3 个参数。
回答by yucun li
friend bool operator==( Rationalnumber l, Rationalnumber r );
when you declare it as non-member function, it can take two arguments. when you declare it as member function, it can only take one argument.
当你将它声明为非成员函数时，它可以接受两个参数。当你将它声明为成员函数时，它只能接受一个参数。
