重载运算符之前++和后++

    <span style="font-family: Arial; font-size: 14px; line-height: 25px;"></span>

下面例子程序中 const Fraction operator ++(int) 中 <br>
int不过是个哑元（dummy）,是永远用不上的 <br>
它只是用来判断＋＋是prefix  还是  postfix <br>
记住，<span style="color: red;">如果有哑元，则是postfix,否则，就是prefix</span><br>
就像其他的一元算法和逻辑运算一样 <br>
而其实在C++中用到这种哑元的也只有在postfix  ++  和--了

例子：

int i=10;<br>
cout<<i++<<endl;<wbr><wbr><wbr>//i=11;后缀加；先返回后自增；<wbr><wbr>10<br>
cout&amp;lt;&amp;lt;++i&amp;lt;&amp;lt;endl;<wbr><wbr><wbr>//i=12;前缀加；先自增后返回；<wbr><wbr>12</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

例：

#include<iostream><br>
using namespace std;

class Fraction<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>//数类；<br>
{<br><wbr>friend ostream&amp;amp; operator&amp;lt;&amp;lt;(ostream&amp;amp; out, const Fraction&amp;amp; x);<br>
private:<br><wbr>int den;<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>//加的步进距离,使自加的距离不是1；<br><wbr>int num;<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>//数（初值）；<br>
public:<br><wbr>Fraction(int d=1, int n=0):den(d),num(n) {}<br><wbr>Fraction&amp;amp; operator++()<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>//前缀自加重载；（前置版本prefix）<br><wbr><wbr>{<br><wbr><wbr><wbr>num+=den;<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>//先自增，再返回；<br><wbr><wbr><wbr>return *this;<br><wbr><wbr>}<br><wbr>const Fraction operator ++(int)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>//后缀自加重载；（后置版本postfix）<br><wbr><wbr>{<br><wbr><wbr><wbr>Fraction old (*this);<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>//拷贝构造（对象参数是对象）。先返回，再自增；<br><wbr><wbr><wbr>++(*this);<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>//调用的是重载的前置版本；<br><wbr><wbr><wbr>return old;<br></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>