下面的代码有没有区别？为什么？
i++; // i的值作为返回值，i自增1
++i; // i自增1，i的值作为返回
示例1：i++ 和 ++i 的区别
Demo
#include <iostream>
#include <string>
using namespace std;
int main()
{
int i = 0;
i++;
++i;
return 0;
}
VS 汇编代码：相同，只有使用的寄存器不同而已 => 在忽略返回值的情况下
#include <iostream>
#include <string>
using namespace std;
int main()
{
000E1C70 push ebp
000E1C71 mov ebp,esp
000E1C73 sub esp,0CCh
000E1C79 push ebx
000E1C7A push esi
000E1C7B push edi
000E1C7C lea edi,[ebp-0CCh]
000E1C82 mov ecx,33h
000E1C87 mov eax,0CCCCCCCCh
000E1C8C rep stos dword ptr es:[edi]
000E1C8E mov ecx,offset _2F191172_main@cpp (0EC02Ah)
000E1C93 call @__CheckForDebuggerJustMyCode@4 (0E128Fh)
int i = 0;
000E1C98 mov dword ptr [i],0 //将0放到标识符i对应的4个字节的内存中
i++;
000E1C9F mov eax,dword ptr [i] //将标识符i所对应的内存中的值传到eax寄存器中
000E1CA2 add eax,1 //将eax寄存器中的值加1
000E1CA5 mov dword ptr [i],eax //将eax寄存器中的值传到标识符i所对应的内存中去
++i;
000E1CA8 mov eax,dword ptr [i]
000E1CAB add eax,1
000E1CAE mov dword ptr [i],eax
return 0;
000E1CB1 xor eax,eax
}
000E1CB3 pop edi
000E1CB4 pop esi
000E1CB5 pop ebx
000E1CB6 add esp,0CCh
000E1CBC cmp ebp,esp
000E1CBE call __RTC_CheckEsp (0E1299h)
000E1CC3 mov esp,ebp
000E1CC5 pop ebp
000E1CC6 ret
分析
【问题】++ 操作符可以重载么？如何区分前置 ++ 和后置 ++ ？
++ 操作符可以被重载
++ 操作符不需要额外的参数++ 操作符需要一个 int 类型的占位参数实例2：++ 操作符的重载
Demo
#include <iostream>
#include <string>
using namespace std;
class Test
{
int mValue;
public:
Test(int i)
{
mValue = i;
}
int value()
{
return mValue;
}
// 成员函数进行前置++操作符重载，返回类引用，没有在栈上生成额外的对象
Test& operator ++ ()
{
++mValue;
return *this;
}
// 成员函数进行后置++操作符重载，返回局部变量
Test operator ++ (int)
{
Test ret(mValue); // 在栈上创建对象，需要调用构造函数、析构函数
mValue++;
return ret;
}
};
int main()
{
Test t(0);
Test t1(0);
cout << t.value() << endl; // 0
cout << t1.value() << endl; // 0
Test tt = t++;
cout << t.value() << endl; // 1
cout << tt.value() << endl; // 0
Test tt1 = ++t1;
cout << t1.value() << endl; // 1
cout << tt1.value() << endl; // 1
return 0;
}
++ 前置和后置真正的区别
对于基础类型的变量
++ 的效率和后置 ++ 的效率基本相同对于类类型的对象
++ 的效率高于后置 ++ ：前置 ++ 返回类引用，没有生成额外的对象，后置返回局部的类对象++ 操作符提高程序效率复数类 Complex 的进一步完善
Demo
// Complex.h
#ifndef COMPLEX_H_
#define _COMPLEX_H_
class Complex
{
double a;
double b;
public:
Complex(double a = 0, double b = 0);
double getA();
double getB();
double getModulus();
Complex operator + (const Complex& c);
Complex operator - (const Complex& c);
Complex operator * (const Complex& c);
Complex operator / (const Complex& c);
bool operator == (const Complex& c);
bool operator != (const Complex& c);
Complex& operator = (const Complex& c);
// 重载++操作符
Complex& operator ++ ();
Complex operator ++ (int);
};
#endif
//Complex.cpp
#include <cmath>
#include "Complex.h"
Complex::Complex(double a, double b)
{
this->a = a;
this->b = b;
}
double Complex::getA()
{
return a;
}
double Complex::getB()
{
return b;
}
double Complex::getModulus()
{
return sqrt(a * a + b * b);
}
Complex Complex::operator + (const Complex& c)
{
double na = a + c.a;
double nb = b + c.b;
Complex ret(na, nb);
return ret;
}
Complex Complex::operator - (const Complex& c)
{
double na = a - c.a;
double nb = b - c.b;
Complex ret(na, nb);
return ret;
}
Complex Complex::operator * (const Complex& c)
{
double na = a * c.a - b * c.b;
double nb = a * c.b + b * c.a;
Complex ret(na, nb);
return ret;
}
Complex Complex::operator / (const Complex& c)
{
double cm = c.a * c.a + c.b * c.b;
double na = (a * c.a + b * c.b) / cm;
double nb = (b * c.a - a * c.b) / cm;
Complex ret(na, nb);
return ret;
}
bool Complex::operator == (const Complex& c)
{
return (a == c.a) && (b == c.b);
}
bool Complex::operator != (const Complex& c)
{
return !(*this == c);
}
Complex& Complex::operator = (const Complex& c)
{
if( this != &c )
{
a = c.a;
b = c.b;
}
return *this;
}
// 重载前置++操作符
Complex& Complex::operator ++ ()
{
a = a + 1;
b = b + 1;
return *this;
}
// 重载后置++操作符
Complex Complex::operator ++ (int)
{
Complex ret(a, b);
a = a + 1;
b = b + 1;
return ret;
}
应用
#include <iostream>
#include "Complex.h"
using namespace std;
int main()
{
Complex c(0,0);
Complex b = ++c;
Complex b1 = c++;
cout << b.getA() << endl; // 1
cout << b.getB() << endl; // 1
cout << b1.getA() << endl; // 0
cout << b1.getB() << endl; // 0
return 0;
}
原文：https://www.cnblogs.com/bky-hbq/p/13903881.html