C++ 函数重载、操作符重载

依然是温故而知新，不过现在更多的是以此为乐的心态啦。本篇通过代码实例，展示c++函数重载相关知识，包括构造函数的重载、操作符重载等。
在构造函数重载中，给大家带来点稍微提升的用法， ~~看了不吃亏，看了不上当~~
鞭策下面的代码吧，以后在某些场景上SHOW一把时，你可能用的上。

#include <iostream>
#include <assert.h>
#include <sal.h>
#include <string>
#include <vector>using namespace std; 知识点
 do{ statement; }while(0) 经常用在宏定义中，减少一些错误的发生
//
#ifdef MYTRACE()
#else
#define MYTRACE() do { std::cout << __FUNCTION__ << ",line" << __LINE__ << std::endl;}while(0)
#endifclass Student
{
public:/// constructStudent(){MYTRACE();}Student( _In_ const std::string name):m_name(name){MYTRACE();}Student(const std::string name,const int age):m_name(name),m_age(age){MYTRACE();}/// copy constructStudent( _In_ const Student& that){this->m_age = that.m_age;this->m_name = that.m_name;MYTRACE();}/// 拷贝赋值Student& operator=(const Student& that){if(this == &that){return *this;}this->m_age = that.m_age;this->m_name = that.m_name;return *this;}/// 操作符重载friend ostream& operator <<(ostream& out,const Student& that){return out << that.m_name << " is " << that.m_age << " years old.";}bool operator !=(const Student& that){return !(that.age() == this->m_age && that.name() == this->m_name);}bool operator ==(const Student& that){return that.age() == this->m_age && that.name() == this->m_name;}/// 常成员函数const int age() const { return m_age;}const std::string name() const { return m_name;}private:int m_age = 0;std::string m_name;
};

Student 中我们使用了C++中的一些基础知识，只能说中规中矩，平平无奇。

class StudentList
{
public:/*********************construct*******************/StudentList(){}StudentList(std::vector<Student> l):m_sl(l){}StudentList(const Student& t){  m_sl.push_back(t); }StudentList(const Student&& t){ m_sl.push_back(t); }/// 禁用拷贝构造和拷贝赋值StudentList(const StudentList& that) = delete;void operator =(const StudentList& that) = delete;/// 玩点儿高级的：参数列表构造void append(const Student& t){ m_sl.push_back(t); }template <typename ...Args>void append(const Student& t, const Args&... args) {m_sl.push_back(t);append(args...);    // 递归}template <typename ...Args>StudentList(const Student& t,const Args&... args){ append(t,args...);}/// 流式构造StudentList& operator<<(const Student& t) { append(t); return *this; }/*********************construct*******************/const std::vector<Student>& data() const{return m_sl;}/******************************* 操作符重载 ************************/friend ostream& operator <<(ostream& out,const StudentList& that){for (const auto& v : that.data()) { out << "(" << v.name() << "," << v.age() << ")" ; }return out;}const Student& operator []( _In_  const unsigned& index)const {assert(index < m_sl.size());return m_sl[index];}const Student& at(_In_ const unsigned& index) const { return m_sl[index];}bool operator !=(const StudentList& that){if(this == &that){return false;}if(this->data().size() == that.data().size()){for(unsigned i = 0; i < that.data().size();++i){if( const_cast<Student&>(this->data()[i])!=  const_cast<Student&>(that.data()[i])){return true;}}}return true;}bool operator ==(const StudentList& that){return !(const_cast<StudentList&>(that) != const_cast<StudentList&>(*this));}/// 这里不做去重处理StudentList& operator +=(const StudentList& that){for(auto v : that.data()){append(v);}return *this;}/******************************* 操作符重载 ************************/private:std::vector<Student> m_sl;
};

StudentList 类中我们做了一些有意思的尝试，譬如让StudentList支持参数列表的初始化,这让他看起来显然cool了一些，其次我们通过重载 operator << 操作符，增加了支持流式的操作。这类似Qt中的

QStringList() << "wo" << "miss" << "u";

是不是瞬间高大上了一些呢。有点像写文章时堆砌的华丽辞藻？显然不是，一些高级语法的应用，其实只是为了让我们的程序更加优雅，更健壮~

int main()
{/// 测试重载的Student构造函数Student st1;Student st2("LiLei",25);Student st3("Keke",26);/// 测试拷贝构造函数Student st4(st3);std::cout << st4 << std::endl;st4 = st2;std::cout << st4 << std::endl;/// list类型参数 构造函数StudentList sl(std::vector<Student>{st2,st3,st4});std::cout << sl << std::endl;/// 参数列表 递归构造函数StudentList sl1{st2,st3,st4,Student("zhanglu",24)};std::cout << sl1 << std::endl;/// 流式构造StudentList sl2;sl2 << st2 << st3 << st4 << Student("zhaoya",25) << Student("lixiu",25);std::cout << sl2 << std::endl;// 测试使用下标重载函数std::cout << sl2[1] << std::endl;std::cout << sl2.at(0) << "   " << sl2.at(1) << std::endl;// std::cout << sl2[6] << std::endl; // error// 测试 != 和 == 操作符std::string sflag = (sl2 != sl2) ? "true" : "false";std::cout <<  sflag << std::endl;sflag = (sl2 == sl2) ? "true" : "false";std::cout <<  sflag << std::endl;sflag = (sl2 != sl1) ? "true" : "false";std::cout <<  sflag << std::endl;// 测试 "+" 操作符StudentList sl3{Student("xiaoli",25)};sl3 += sl2;std::cout <<  sl3 << std::endl;return 0;
}