STL - vector的使用

最新推荐文章于 2025-05-30 11:29:38 发布

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最新推荐文章于 2025-05-30 11:29:38 发布

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文章标签： STL vector reserve resize push pop

本文链接：https://blog.youkuaiyun.com/J4Ya_/article/details/80729947

本文深入讲解了C++标准库中的vector容器，包括其内部结构、迭代器操作、成员函数及常用接口的使用方法。通过丰富的代码示例展示了如何高效地使用vector进行数据管理。

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vector结构

start指向这块空间的起始位置

finish指向有效元素的后一个位置

end_of_storage指向这块空间的下一个位置

vector的迭代器

vector迭代器的底层其实就是一个原生指针,对迭代器的 ++ 等同于对指针做 ++ 操作,对迭代器的解引用 (*) 等同于对原生指针解引用,取其内容.

vector迭代器的操作(图片截取自cplusplus):

这里演示begin,end,rbegin,rend

#include <iostream>
using namespace std;
#include <vector>

void test_iterator()
{
    vector<int> v;
    v.push_back(1);
    v.push_back(2);
    v.push_back(3);
    v.push_back(4);

    vector<int>::iterator it = v.begin();
    while(it != v.end())
    {
        cout<<*it<<" ";
        ++it;
    }
    cout<<endl;

    vector<int>::reverse_iterator rit = v.rbegin();
    while(rit != v.rend())
    {
        cout<<*rit<<" ";
        ++rit;
    }
    cout<<endl;
}

int main()
{
    test_iterator();
    return 0;
}

运行结果:

vector的成员函数

(图片截取自cplusplus)

验证vector的构造函数

void test_constructor()
{
    //1.直接构造一个空的顺序表
    vector<int> v1;
    cout<<"v1.size() = "<<v1.size()<<endl;
    cout<<"v1.capacity() = "<<v1.capacity()<<endl;

    //2.构造一个空的顺序表,但是空间大小设置为20
    vector<int> v2(20);
    cout<<"v2.size() = "<<v2.size()<<endl;
    cout<<"v2.capacity() = "<<v2.capacity()<<endl;

    //3.构造一个arr对象,并使用arr对vector进行初始化
    int arr[] = {1,2,3,4,5,6};
    vector<int> v3(arr,arr+sizeof(arr)/sizeof(arr[0]));
    cout<<"v3.size() = "<<v3.size()<<endl;
    cout<<"v3.capacity() = "<<v3.capacity()<<endl;

    //4.构造一个vector,期中有4个值为100的元素
    vector<int> v4(4,10);
    cout<<"v4.size() = "<<v4.size()<<endl;
    cout<<"v4.capacity() = "<<v4.capacity()<<endl;
    PrintVector(v4);
}

运行结果:

由此可见,构建vector可以是一个空的vector,也可以用一块固定长度空间,也可以对这块空间初始化.

常用接口介绍

push_back,pop_back,erase,insert

这四个接口的用法很简单,有过一些数据结构基础的朋友一定很快就能上手.

void test_push_pop_insert_erase()
{
    vector<int> v;
    v.push_back(1);
    v.push_back(2);
    v.push_back(3);
    v.push_back(4);
    cout<<"尾插4个元素"<<endl;
    PrintVector(v);
    v.pop_back();
    v.pop_back();
    cout<<"尾删两个元素"<<endl;
    PrintVector(v);
    cout<<"在最前面插入0"<<endl;
    v.insert(v.begin(),0);
    PrintVector(v);
    cout<<"删除最前面的0"<<endl;
    v.erase(v.begin());
    PrintVector(v);
}

运行结果:

push_back和pop_back都很好理解,我们重点看一下erase和insert(图片截取自cplusplus)

我们可以看到,erase和insert都是配合迭代器使用的.两个函数不仅可以删除一个值,也可以删除一段区间.

void test_insert_erase()
{
    vector<int> v(5,10);
    cout<<"起始vector"<<endl;
    PrintVector(v);
    cout<<"在起始位置插入5个0"<<endl;
    v.insert(v.begin(),5,0);
    PrintVector(v);
    cout<<"删除起始位置的5个值"<<endl;
    v.erase(v.begin(),v.begin()+5);
    PrintVector(v);
}

结果演示:

clear,assign

首先看一下clear和assign的用法(图片截取自cplusplus)

void test_clear_assign()
{
    vector<int> v;
    v.assign(8,5);
    cout<<"assign(8,5)"<<endl;
    PrintVector(v);
    cout<<"size = "<<v.size()<<endl;
    cout<<"capacity = "<<v.capacity()<<endl;
    cout<<"----------------------"<<endl;

    v.clear();
    cout<<"after clear"<<endl;
    PrintVector(v);
    cout<<"size = "<<v.size()<<endl;
    cout<<"capacity = "<<v.capacity()<<endl;
    cout<<"----------------------"<<endl;

    v.assign(4,5);
    cout<<"assign(4,5)"<<endl;
    PrintVector(v);
    cout<<"size = "<<v.size()<<endl;
    cout<<"capacity = "<<v.capacity()<<endl;
    cout<<"----------------------"<<endl;


    v.assign(6,10);
    cout<<"assign(6,10)"<<endl;
    PrintVector(v);
    cout<<"size = "<<v.size()<<endl;
    cout<<"capacity = "<<v.capacity()<<endl;
    cout<<"----------------------"<<endl;

    int arr[] = {1,2,3,4,5,6,7};
    v.assign(arr,arr+sizeof(arr)/sizeof(arr[0]));
    cout<<"assign(arr,arr+5)"<<endl;
    PrintVector(v);
    cout<<"size = "<<v.size()<<endl;
    cout<<"capacity = "<<v.capacity()<<endl;
}

结果演示:

由结果可以看出,clear清除vector,只清除有效区间,也就是将 finish置为start,但是不清除空间,也就是 end_of_storage 不改变

assign总结: assign(m,n)是置m个n值

当m的大小小于capacity时,会将这段空间的有效区间(size)置为m,并且将值都改为n

当m的大小大于capacity时,会将size和capacity都修改为m,并且赋值为n

assign也可以用一段空间来修改

reserve,resize

reserve : 主要用于当你已知自己将需要多大的空间时,就预先开好,避免在插入数据时扩容,可以提高效率.reserve只预先开好capacity

resize : 主要用于当你已知自己需要的有效空间的大小,可以预先开好空间,并且初始化.resize会预先开好capacity和size

void test_reserve_resize()
{
    vector<int> v1;
    v1.reserve(10);
    cout<<"v1.reserve(10)"<<endl;
    cout<<"size = "<<v1.size()<<endl;
    cout<<"capacity = "<<v1.capacity()<<endl;
    cout<<"----------------------"<<endl;

    v1.reserve(5);
    cout<<"v1.reserve(5)"<<endl;
    cout<<"size = "<<v1.size()<<endl;
    cout<<"capacity = "<<v1.capacity()<<endl;
    cout<<"----------------------"<<endl;

    vector<int> v2;
    v2.resize(5,5);
    cout<<"v2.resize(5,5)"<<endl;
    PrintVector(v2);
    cout<<"size = "<<v2.size()<<endl;
    cout<<"capacity = "<<v2.capacity()<<endl;
    cout<<"----------------------"<<endl;

    v2.resize(2,2);
    cout<<"v2.resize(2,2)"<<endl;
    PrintVector(v2);
    cout<<"size = "<<v2.size()<<endl;
    cout<<"capacity = "<<v2.capacity()<<endl;
    cout<<"----------------------"<<endl;

    v2.resize(10,10);
    cout<<"v2.resize(10,10)"<<endl;
    PrintVector(v2);
    cout<<"size = "<<v2.size()<<endl;
    cout<<"capacity = "<<v2.capacity()<<endl;

}

运行结果:

观察结果我们可以看出,reserve只开空间,当开的空间比当前空间小的时候,并不改变空间大小.

resize(m,n),当m比当前空间小的时候,会将有效空间修改为m,当m比当前空间大的时候,会将size和capacity置为m

整体代码

#include <iostream>
using namespace std;
#include <vector>

void PrintVector(vector<int> v)
{
    vector<int>::iterator it = v.begin();
    while(it != v.end())
    {
        cout<<*it<<" ";
        ++it;
    }
    cout<<endl;
}

void test_iterator()
{
    vector<int> v;
    v.push_back(1);
    v.push_back(2);
    v.push_back(3);
    v.push_back(4);

    vector<int>::iterator it = v.begin();
    while(it != v.end())
    {
        cout<<*it<<" ";
        ++it;
    }
    cout<<endl;

    vector<int>::reverse_iterator rit = v.rbegin();
    while(rit != v.rend())
    {
        cout<<*rit<<" ";
        ++rit;
    }
    cout<<endl;
}

void test_constructor()
{
    //1.直接构造一个空的顺序表
    vector<int> v1;
    cout<<"v1.size() = "<<v1.size()<<endl;
    cout<<"v1.capacity() = "<<v1.capacity()<<endl;

    //2.构造一个空的顺序表,但是空间大小设置为20
    vector<int> v2(20);
    cout<<"v2.size() = "<<v2.size()<<endl;
    cout<<"v2.capacity() = "<<v2.capacity()<<endl;

    //3.构造一个arr对象,并使用arr对vector进行初始化
    int arr[] = {1,2,3,4,5,6};
    vector<int> v3(arr,arr+sizeof(arr)/sizeof(arr[0]));
    cout<<"v3.size() = "<<v3.size()<<endl;
    cout<<"v3.capacity() = "<<v3.capacity()<<endl;

    //4.构造一个vector,期中有4个值为100的元素
    vector<int> v4(4,10);
    cout<<"v4.size() = "<<v4.size()<<endl;
    cout<<"v4.capacity() = "<<v4.capacity()<<endl;
    PrintVector(v4);
}

void test_push_pop_insert_erase()
{
    vector<int> v;
    v.push_back(1);
    v.push_back(2);
    v.push_back(3);
    v.push_back(4);
    cout<<"尾插4个元素"<<endl;
    PrintVector(v);
    v.pop_back();
    v.pop_back();
    cout<<"尾删两个元素"<<endl;
    PrintVector(v);
    cout<<"在最前面插入0"<<endl;
    v.insert(v.begin(),0);
    PrintVector(v);
    cout<<"删除最前面的0"<<endl;
    v.erase(v.begin());
    PrintVector(v);
}

void test_insert_erase()
{
    vector<int> v(5,10);
    cout<<"起始vector"<<endl;
    PrintVector(v);
    cout<<"在起始位置插入5个0"<<endl;
    v.insert(v.begin(),5,0);
    PrintVector(v);
    cout<<"删除起始位置的5个值"<<endl;
    v.erase(v.begin(),v.begin()+5);
    PrintVector(v);
}

void test_clear_assign()
{
    vector<int> v;
    v.assign(8,5);
    cout<<"assign(8,5)"<<endl;
    PrintVector(v);
    cout<<"size = "<<v.size()<<endl;
    cout<<"capacity = "<<v.capacity()<<endl;
    cout<<"----------------------"<<endl;

    v.clear();
    cout<<"after clear"<<endl;
    PrintVector(v);
    cout<<"size = "<<v.size()<<endl;
    cout<<"capacity = "<<v.capacity()<<endl;
    cout<<"----------------------"<<endl;

    v.assign(4,5);
    cout<<"assign(4,5)"<<endl;
    PrintVector(v);
    cout<<"size = "<<v.size()<<endl;
    cout<<"capacity = "<<v.capacity()<<endl;
    cout<<"----------------------"<<endl;


    v.assign(6,10);
    cout<<"assign(6,10)"<<endl;
    PrintVector(v);
    cout<<"size = "<<v.size()<<endl;
    cout<<"capacity = "<<v.capacity()<<endl;
    cout<<"----------------------"<<endl;

    int arr[] = {1,2,3,4,5,6,7};
    v.assign(arr,arr+sizeof(arr)/sizeof(arr[0]));
    cout<<"assign(arr,arr+5)"<<endl;
    PrintVector(v);
    cout<<"size = "<<v.size()<<endl;
    cout<<"capacity = "<<v.capacity()<<endl;
}

void test_reserve_resize()
{
    vector<int> v1;
    v1.reserve(10);
    cout<<"v1.reserve(10)"<<endl;
    cout<<"size = "<<v1.size()<<endl;
    cout<<"capacity = "<<v1.capacity()<<endl;
    cout<<"----------------------"<<endl;

    v1.reserve(5);
    cout<<"v1.reserve(5)"<<endl;
    cout<<"size = "<<v1.size()<<endl;
    cout<<"capacity = "<<v1.capacity()<<endl;
    cout<<"----------------------"<<endl;

    vector<int> v2;
    v2.resize(5,5);
    cout<<"v2.resize(5,5)"<<endl;
    PrintVector(v2);
    cout<<"size = "<<v2.size()<<endl;
    cout<<"capacity = "<<v2.capacity()<<endl;
    cout<<"----------------------"<<endl;

    v2.resize(2,2);
    cout<<"v2.resize(2,2)"<<endl;
    PrintVector(v2);
    cout<<"size = "<<v2.size()<<endl;
    cout<<"capacity = "<<v2.capacity()<<endl;
    cout<<"----------------------"<<endl;

    v2.resize(10,10);
    cout<<"v2.resize(10,10)"<<endl;
    PrintVector(v2);
    cout<<"size = "<<v2.size()<<endl;
    cout<<"capacity = "<<v2.capacity()<<endl;

}

int main()
{
    /* test_iterator(); */
    /* test_constructor(); */
    /* test_push_pop_insert_erase(); */
    /* test_insert_erase(); */
    /* test_clear_assign(); */
    test_reserve_resize();
    return 0;
}