运算符++中的Int参数 [英] Int Argument in operator++

问题描述

class myClass
{
    public:

    void operator++()
    {
        // ++myInstance.
    }

    void operator++(int)
    {
        // myInstance++.
    }
}

除了允许编译器区分 myInstance ++ 和 ++ myInstance 是<$ c $中的可选 int c> operator ++ 实际上什么？

Besides letting the compiler distinguish between myInstance++ and ++myInstance, is the optional int argument in operator++ actually for anything? If so, what is it?

推荐答案

正如@Konrad所说，int参数不用于任何东西，除了distingush

As @Konrad said, the int argument is not used for anything, other than to distingush between the pre-increment and post-increment forms.

请注意，您的运算符应该返回一个值。预增量应返回一个引用，后增量应返回值。机智：

Note however that your operators should return a value. Pre-increment should return a reference, and post-increment should return by-value. To wit:

class myClass
{

public:

myClass& operator++()
{
    // ++myInstance. 
    return * this;   
}
myClass operator++(int)
{
    // myInstance++.
    myClass orig = *this;
    ++(*this);  // do the actual increment
    return orig;
}
};

编辑：

正如Gene Bushuyev提到的正确地在下面，并不是绝对要求 operator ++ 返回非空值。然而，在大多数情况下（我不能想到一个例外），你需要。特别是如果你想把运算符的结果赋给一些其他的值，比如：

As Gene Bushuyev mentions correctly below, it is not an absolute requirement that operator++ return non-void. However, in most cases (I can't think of an exception) you'll need to. Especially if you want to assign the results of the operator to some other value, such as:

myClass a;
myClass x = a++;

EDIT2：

postimcrement版本，你将在对象递增之前返回。这通常使用本地临时实现。见上文。

Also, with the postimcrement version, you will return the object before it was incremented. This is typically done using a local temporary. See above.

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