C++ 中的运算符重载

发布于 2024-10-21 05:46:56 字数 302 浏览 4 评论 0原文

所以我正在参加基础编程 II 课程。我们必须创建一个程序来实现 4 个不同的功能，从而改变操作员的工作方式。我已经查找了多个示例和多组文本来显示如何执行此操作，但我无法确定任何代码的含义。对我来说这样的事情应该有效。

int operator++()
{
    variableA--;
}

对我来说，这表示如果您遇到 ++，那么 - 从变量来看，现在显然它不会像这样工作。我发现的所有示例都创建了自己的数据类型。有没有办法使用 int 或 double 重载运算符？

原文

So I'm in a basic programming II class. We have to create a program that makes 4 different functions that will change the way an operator works. I've looked up multiple examples and sets of text that display how to do this, but I cannot make which way of what any of the code means. To me something like this should work.

int operator++()
{
    variableA--;
}

To me, this says if you encounter a ++, then -- from the variable, now obvious it doesn't work like this. All the examples I've found create their own data type. Is there a way to overload an operator using an int or a double?

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雪落纷纷 2024-10-28 05:46:56

所有示例都创建自己的数据类型，因为这是运算符重载的规则之一：重载运算符必须至少适用于一种用户定义类型。

即使您可以为整数重载++，编译器也不知道要使用哪一个——您的版本还是常规版本；这会是模棱两可的。

您似乎将运算符视为单个函数，但每个重载都是一个完全独立的函数，通过其函数签名（类型，有时是参数数量）来区分，同时具有相同的运算符符号（这是“重载”的定义）。

因此，您不能重载 ++ 来总是做不同的事情；这实际上是运算符重写，C++ 不允许这样做。

您可以为您创建的类型定义 ++：

class MyType {
public:
    int value;
};

MyType const& operator++(MyType& m) {   // Prefix
    ++m.value;
    return m;
}

const MyType operator++(MyType& m, int) {   // Postfix (the 'int' is just to differentiate it from the prefix version)
    MyType temp = m;
    ++m.value;
    return temp;
}

int main() {
    MyType m;
    m.value = 0;
    m++;    // Not m.value++
    cout << m.value;    // Prints 1
}

请注意，这组 ++ 运算符是在 MyType 类外部定义的，但也可以在内部定义相反（他们可以通过这种方式访问非公共成员），尽管他们的实现会略有不同。

All the examples create their own data type since this is one of the rules for operator overloading: An overloaded operator must work on at least one user-defined type.

Even if you could overload ++ for integers, the compiler wouldn't know which one to use -- your version or the regular version; it would be ambiguous.

You seem to think of operators as single functions, but each overload is a completely separate function differentiated by its function signature (type and sometimes number of arguments), while having the same operator symbol (this is the definition of "overloading").

So, you can't overload ++ to always do something different; this would really be operator overriding, which C++ doesn't allow.

You can define ++ for a type you've created though:

class MyType {
public:
    int value;
};

MyType const& operator++(MyType& m) {   // Prefix
    ++m.value;
    return m;
}

const MyType operator++(MyType& m, int) {   // Postfix (the 'int' is just to differentiate it from the prefix version)
    MyType temp = m;
    ++m.value;
    return temp;
}

int main() {
    MyType m;
    m.value = 0;
    m++;    // Not m.value++
    cout << m.value;    // Prints 1
}

Note that this set of ++ operators was defined outside of the MyType class, but could have been defined inside instead (they would gain access to non-public members that way), though their implementations would be a little different.

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