operator++ 中的整数参数 [英] Int Argument in operator++

问题描述

class myClass
{
    public:

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

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

除了让编译器区分 myInstance++ 和 ++myInstance 之外，还有 operator++ 中的可选 int 参数实际上是为了什么?如果是，那是什么?

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 参数不用于任何事情，除了区分前增量和后增量形式.

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

但是请注意，您的运算符应该返回一个值.前增量应该返回一个引用，后增量应该返回按值.即:

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;
}
};

正如 Gene Bushuyev 在下面正确提到的，operator++ 返回非空并不是绝对的要求.但是，在大多数情况下(我想不出例外)，您需要这样做.特别是如果您想将运算符的结果分配给某个其他值，例如:

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++;

此外，使用 postimcrement 版本，您将在对象递增之前返回对象.这通常是使用本地临时文件完成的.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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