vector的使用

迈不过友情╰ 2022-06-08 13:44 161阅读 0赞

#include<iostream>
    #include <vector>
    
    using namespace std;
    
    int main(){
        unsigned int i;
        vector<int> first;
        vector<int> second(4,100);
        vector<int> third(second.begin(),second.end());
        vector<int> forth{
       0,1,2,3,4,5,6,7,8,9,0};
    
        int mytins[]={
       16,2,22,7,11};
        vector<int> fifth(mytins,mytins+sizeof(mytins)/sizeof(int));
        cout << "the fifth contains ";
        for(auto h:fifth)
            cout << h << " ";
        cout << endl;
    
        //assign()函数一共包含两个版本第一个支持重复数字的引用版本,第二个支持迭代器版本;
        first.assign(7,100);
        for(auto h:first)
            cout << h << " ";
        cout << endl;
        first.assign(10,1);
        for(auto h:first)
            cout << h << " ";
        cout << endl;
        first.assign(second.begin(),second.end());
        for(auto h:first)
            cout << h << " ";
        cout << endl;
        first.assign(second.begin(),second.end());
        //at用来作为下标访问
        for(size_t i=0;i<forth.size();++i)
            cout << forth.at(i) << " ";
        cout << endl;
        //.back()用于返回当前vector的最后一个元素;
        cout << forth.back() << endl;
        //.begin() .end()两个迭代器,用于访问vector里面的元素
        for(auto It=forth.begin();It!=forth.end();++It)
            cout << *It << " ";
        cout << endl;
        //auto 可以使用vector<int>::iterator It 进行代替;
    
        //capacity() vector里面已经分配的空间的大小,用来衡量里面可以访问多少元素;
        cout << "first.capacity(): " << first.capacity() <<"\tfirst.size(): " << (int)first.size() << endl;  
        cout << "second.capacity(): " << second.capacity() <<"\tsecond.size(): " << second.size() << endl; 
        cout << "third.capacity(): " << third.capacity() <<"\tthird.size(): " << third.size() << endl;  
        cout << "forth.capacity(): " << forth.capacity() <<"\tforth.size(): " << forth.size() << endl;  
        cout << "fifth.capacity(): " << fifth.capacity() <<"\tfifth.size(): " << fifth.size() << endl;  
        //clear 调用析构函数,将所有元素清0,并且将size置为0,但是分配的空间大小是没有改变的;
        first.clear();
        cout << first.capacity() << endl;
        cout << first.size() << endl;
    
        //.erase()擦出某些函数,一共有两个版本,其中一个是传递位置,另一个是传递范围,两者都必须是迭代器
        for(size_t i=0;i<20;++i)
            first.push_back(i);
        first.erase(first.begin()+2);
        for(auto h:first)
            cout << h << " ";
        cout << endl;
    
        first.erase(first.begin()+2,first.begin()+7);
        for(auto h:first)
            cout << h << " ";
        cout << endl;
        //.front()用于返回当前容器的第一个元素;
        cout << "first.front(): " << first.front() << endl;
        //.get_allocator()用于获得分配容器的适配器,可以使用这个适配器用来获得需要的空间;
        int *p;
        vector<int> myvector;
        //使用指针获得5个元素的分配地址;
        p=myvector.get_allocator().allocate(5);
        for(auto i=0;i<5;++i)
            p[i]=i;
        for(auto i=0;i<5;++i)
            cout << p[i] << " ";
        cout << endl;
    
        //Insert 用于在当前容器里面插入元素,支持三种形式的插入:(位置,元素),(位置,元素数量,元素),(位置,迭代器开始,迭代器结束);
        forth.insert(forth.begin()+5,10);
        forth.insert(forth.begin()+3,4,5);
        forth.insert(forth.begin()+7,first.begin(),first.end());
        for(auto h:forth)
            cout << h << " ";
        cout << endl;
    
        //=用于完成元素的拷贝,并且丢弃原来数组里面的元素
    
        vector<int> vfirst;
        first=vfirst;
        for(auto h:first)
            cout << h << " ";
        cout << endl;
        for(size_t i=0;i<forth.size();++i)
            forth[i]=i*2;
        for(size_t i=0;i<forth.size();++i)
            cout << forth[i] << " ";
        cout << endl;
        //.pop.back()用于逐个的删除容器里面的元素;
        while(second.empty()){
            second.pop_back();
        }
        //.rebegin() rend()用于从后往前进行迭代器的遍历;
        for(auto It=forth.rbegin();It!=forth.rend();++It)
            cout << *It << " ";
        cout << endl;
        //用来主动要求capacity的大小,函数原型void reverse(size_t n);
        vector<int> newvector;
        newvector.resize(20);
        cout << "newvector.capacity: " << newvector.capacity() << endl;
        //.resize():一共有三种情况,如果设定的n的值小于当前的数字元素实际大小,那么超过的部分就会被销毁;
        //如果n大于当前实际元素的大小,那么容器里面会被填充其他的元素;
        //如果n大于capacity的大小,那么容器会自动调整capacity的大小;
        vector<int> mynewvector;
        for(size_t i=0;i<10;i++)
            mynewvector.push_back(i);
        mynewvector.resize(5);
        mynewvector.resize(8,100);
        for(auto my:mynewvector)
            cout << my << " ";
        cout << endl;
        //.shrink_to_fit:请求减少capacity适应size的大小;
        //这个过程使可以自动进行优化的,有可能进行空间的重新分配,但是不会原始的数据;
        vector<int> mynewvector1(100);
        cout << "capacity of mynewvector1: " << mynewvector1.capacity() << endl;
        mynewvector1.resize(10);
        cout << "capacity of mynewvector1: " << mynewvector1.capacity() << endl;
        myvector.shrink_to_fit();
        cout << "capacity of mynewvector1: " << mynewvector1.capacity() << endl;
        //size:用来衡量容器里面实际元素的数量
        cout << "myvector.size(): " << myvector.size() << endl;
        //.swap()用来交换两个容器里面的元素
        second.swap(fifth);
        cout << "second contains: " ;
        for(auto nh:second)
            cout << nh << " ";
        cout << endl;
        cout << "fifth contains: ";
        for(auto hh:fifth)
            cout << hh << " ";
        cout << endl;
    }