c++容器和函数对象（仿函数）

Posted 2021-12-22 程序彤

vector、set、map容器

vector和set的声明和遍历

vector的嵌套，大vector中嵌套多个小vector

#include <iostream>
#include <vector>

using namespace std;

void test1() 
    vector<vector<int> > vec;
    vector<int> v1;
    vector<int> v2;
    vector<int> v3;
    for (int i = 0; i < 4; i++) 
        v1.push_back(i + 1);
        v2.push_back(i + 2);
        v3.push_back(i + 3);
    
    vec.push_back(v1); // 将三个vector容器放入一个大vector容器中
    vec.push_back(v2);
    vec.push_back(v3);
    // 遍历嵌套容器
//    for (vector<vector<int> >::iterator it = vec.begin(); it < vec.end(); it++) 
//        for (vector<int>::iterator vit = (*it).begin(); vit < (*it).end(); vit++)  // *it只解引用出的小容器
//            cout << (*vit) << " ";
//        
//        cout << endl;
//    
    // 使用auto也可实现遍历
    for (auto it = vec.begin(); it < vec.end(); it++) 
        for (auto vit = (*it).begin(); vit < (*it).end(); vit++)  // *it只解引用出的小容器
            cout << (*vit) << " ";
        
        cout << endl;
    


int main() 
    test1();
    return 0;

map的声明和遍历

#include <iostream>
#include <set>
#include <map>

using namespace std;

//class MyCompare 
//public:
//    bool operator()(int v1, int v2) 
//        return v1>v2;
//    
//;

// 传入指针也可！打印map下的数据
void printMap(map<int, int> *map1) 
    for (map<int, int>::iterator it = map1->begin(); it != map1->end(); it++) 
        cout << "key:" << (*it).first << " value:" << (*it).second << endl;
    


//void printMap2(map<int, int,MyCompare> *mapn) 
//    for (map<int, int, MyCompare>::iterator it = mapn->begin(); it != mapn->end(); it++) 
//        cout << "key:" << (*it).first << " value:" << (*it).second << endl;
//    
//

int main() 
    // set
    set<int> s;
    s.insert(20);
    s.insert(10);
    s.insert(40);
    s.insert(30);

    pair<set<int>::iterator, bool> ret = s.insert(10);
    if (ret.second) 
        cout << "successful!" << endl;
        return 0;
    
    cout << "fail" << endl;

    // map
    map<int, int> map1;
    map1.insert(pair<int, int>(1, 666));
    map1.insert(make_pair(2, 777)); // 这样也可制造对组
    map1.insert(make_pair(3, 888));

    printf("------------\\n");
    printMap(&map1);
    printf("------------\\n");
    map<int, int>::iterator pos = map1.find(1);
    if (pos != map1.end()) 
        cout << "key为" << pos->first << " value为" << pos->second << endl;
//        return 0;
     else 
        cout << "未找到该key对应的value" << endl;
    
    printf("------------");

//    map<int, int, MyCompare> map2;
//    map2.insert(pair<int, int>(1, 666));
//    map2.insert(make_pair(2, 777)); // 这样也可制造对组
//    map2.insert(make_pair(3, 888));
    printMap2(&map2);
//    for (map<int, int, MyCompare>::iterator it = map2.begin(); it != map2.end(); it++) 
//        cout << "key:" << (*it).first << " value:" << (*it).second << endl;
//    
    return 0;

map仿函数（函数对象）

当给对象排序时，必须使用仿函数（即类）
bool operator()(int k1, int k2) const // 仅根据key排序 return k1 > k2;

#include <iostream>
#include <map>

using namespace std;

class MyCompare 
public:
    // 警告：这里不加const将运行报错！！！
    bool operator()(int k1, int k2) const  // 仅根据key排序
        return k1 > k2;
    
;

int main() 

    map<int, int, MyCompare> map2;
    map2.insert(pair<int, int>(1, 666));
    map2.insert(make_pair(2, 999)); // 这样也可制造对组
    map2.insert(make_pair(3, 888));
//    printMap2(&map2);
    for (map<int, int, MyCompare>::iterator it = map2.begin(); it != map2.end(); it++) 
        cout << "key:" << (*it).first << " value:" << (*it).second << endl;
    
    return 0;

函数对象的三种使用方式

#include <iostream>

using namespace std;

/**
 * 仿函数，函数对象，本质 类。
 */
class MyAdd 
public:
    int operator()(int a, int b) 
        return a + b;
    
;

class MyPrint 
public:
    int count;

    MyPrint() 
        this->count = 0;
    

    void operator()(string text) 
//        this->count++; // 阔以~
        count++;
        cout << text << endl;
    
;

void test1() 
    MyAdd myAdd;
    int ret = myAdd(1, 2);
    cout << "ret:" << ret << endl;


void test2() 
    MyPrint myPrint;
    myPrint("lwt1");
    myPrint("lwt2");
    myPrint("lwt3");
    cout << "调用仿函数的次数：" << myPrint.count << endl;


void doPrint(MyPrint &mp,string text)
    mp(text);

void test3()
    MyPrint myPrint;
    doPrint(myPrint,"void doPrint(MyPrint &mp,string text) lwt666");

int main() 
    test1();
    test2();
    test3();
    return 0;