multiset学习之创建，初始化，赋值操作operator=, empty,size

本篇开始学习multiset，与set相比，multiset可以有多个相关的关键字，其它也set的功能一样，下面我们先来学习它的创建，初始化，赋值操作operator=, empty,size等相关操作。

代码示例：

#include <iostream>
#include <set>
#include <string>
#include <functional>
#include <cmath>using namespace std;bool fncomp_greater (int lhs, int rhs) {return lhs > rhs;}bool fncomp_less (int lhs, int rhs) {return lhs < rhs;}struct classcomp_less {bool operator() (const int& lhs, const int& rhs) const{return lhs < rhs;}
};struct classcomp_greater {bool operator() (const int& lhs, const int& rhs) const{return lhs > rhs;}
};struct Point { int x, y; };
struct PointCmp_greater {bool operator()(const Point& lhs, const Point& rhs) const {return std::hypot(lhs.x, lhs.y) > std::hypot(rhs.x, rhs.y);//hypot计算三解形的斜边长}
};
struct PointCmp_less {bool operator()(const Point& lhs, const Point& rhs) const {return std::hypot(lhs.x, lhs.y) < std::hypot(rhs.x, rhs.y);}
};void multisetInit()
{//1.创建multisetstring strVal[] = {"first", "second", "three", "fifth"};multiset<string> set1(strVal, strVal + 4);cout << "set1.size = " << set1.size() << " set1.empty = " << set1.empty() << " set1.max_size = " << set1.max_size() << endl;cout << "set1.size = " << set1.size() << " set1.empty = " << set1.empty() << " set1.max_size = " << set1.max_size() << endl;cout << "set1的值为：  ";multiset<string>::iterator iter1;for(iter1 = set1.begin(); iter1 != set1.end(); iter1++){cout << *iter1 << "\t";}cout << endl;//2.列表初始化multiset<int> set2 = {1, 2, 3, 4};cout << "set2.size = " << set2.size() << " set2.empty = " << set2.empty() << " set2.max_size = " << set2.max_size() << endl;cout << "set2的值为：  ";for(auto &val: set2){cout << val << "\t";}cout << endl;//3.赋值初始化multiset<int> set3 = set2;cout << "set3的值为：  ";for(auto &val: set3){cout << val << "\t";}cout << endl;//4.拷贝初始化multiset<string> set4(set1);cout << "set4.size = " << set4.size() << " set4.empty = " << set4.empty() << " set4.max_size = " << set4.max_size() << endl;cout << "set4的值为：  ";for(auto &val: set4){cout << val << "\t";}cout << endl;//5.范围初始化multiset<int> set5(set2.begin(), set2.end());cout << "set5.size = " << set5.size() << " set5.empty = " << set5.empty() << " set5.max_size = " << set5.max_size() << endl;cout << "set5的值为：  ";for(auto &val: set5){cout << val << "\t";}cout << endl;//6.移动构造函数multiset<string> set6(std::move(set1));cout << "set6.size = " << set6.size() << " set6.empty = " << set6.empty() << " set6.max_size = " << set6.max_size() << endl;auto iter6 = set6.begin();cout << "set6的值为：  ";while (iter6 != set6.end()){cout << *iter6 << "\t";iter6++;}cout << endl;cout << "-----------------------" << endl;// class as Comparestd::multiset<int> set7 = {1, 7, 3, 4, 3};auto iter7 = set7.begin();//默认是升序输出的cout << "默认是升序输出的  set7的值为：  ";while (iter7 != set7.end()){cout << *iter7 << "\t";iter7++;}cout << endl;std::multiset<int, classcomp_less> set8 = {1, 7, 3, 4, 3};auto iter8 = set8.begin();cout << "升序输出        set8的值为：  ";//升序输出while (iter8 != set8.end()){cout << *iter8 << "\t";iter8++;}cout << endl;std::multiset<int, classcomp_greater> set9 = {1, 7, 3, 4, 3};auto iter9 = set9.begin();cout << "降序输出        set9的值为：  ";//降序输出while (iter9 != set9.end()){cout << *iter9 << "\t";iter9++;}cout << endl;//也可以调用系统自带的比较函数，例如greater,less, 要包含头文件functionalstd::multiset<int, greater<int>> set10 = {1, 7, 3, 4, 3};auto iter10 = set10.begin();cout << "降序输出 set10的值为：  ";//降序输出while (iter10 != set10.end()){cout << *iter10 << "\t";iter10++;}cout << endl;std::multiset<int, less<int>> set11 = {1, 7, 3, 4, 3};auto iter11 = set11.begin();cout << "升序输出 set11的值为：  ";//降序输出while (iter11 != set11.end()){cout << *iter11 << "\t";iter11++;}cout << endl;bool(*fn_pt)(int,int) = fncomp_less;std::multiset<int, bool(*)(int,int)> set12 (fn_pt);  // function pointer as Compareset12.insert(1);set12.insert(7);set12.insert(4);set12.insert(3);auto iter12 = set12.begin();cout << "升序输出 set12的值为：  ";//降序输出while (iter12 != set12.end()){cout << *iter12 << "\t";iter12++;}cout << endl;bool(*fn_pt_greater)(int,int) = fncomp_greater;std::multiset<int, bool(*)(int,int)> set13 (fn_pt_greater);set13.insert(1);set13.insert(7);set13.insert(4);set13.insert(3);auto iter13 = set13.begin();cout << "升序输出 set13的值为：  ";//升序输出while (iter13 != set13.end()){cout << *iter13 << "\t";iter13++;}cout << endl;//自定义类型比较std::multiset<Point, PointCmp_greater> set14 = {{1, 2}, {7, 8}, {3, 4}, {3, 5}};set14.insert({8, 7}); // 这会失败，因为 8，7 的斜边长度等于 7,8cout << "降序输出 set14的值为：    ";for(auto& p: set14)cout << '(' << p.x << ',' << p.y << ") ";cout << endl;std::multiset<Point, PointCmp_less> set15 = {{1, 2}, {7, 8}, {3, 4}, {3, 5}};set15.insert({8, 7});cout << "升序输出 set15的值为：    ";for(auto& p: set15)cout << '(' << p.x << ',' << p.y << ") ";cout << endl;
}int main()
{multisetInit();cout << "Hello, world!" << endl;return 0;
}

运行结果：

参考：

https://zh.cppreference.com/w/cpp/container/multiset

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