C++ vector库学习笔记

vector是C++标准模板库，它是一个多功能、能够操作多种数据结构和算法的模板类。vector是一个容器，能够像容器一样存放各种类型的对象。vector是一个能够存放任意类型的动态数组，能够增加和删除元素，可以完全替代C语言风格的动态数组，由于vector能够自动的管理内存，我们不需要考虑内存的增长和释放、具有很好的安全性。

vector的初始化

//定义具有10个整型元素的向量
//（尖括号为元素类型名，它可以是任何合法的数据类型），
//不具有初值，其值不确定
vector<int>a(10);//定义具有10个整型元素的向量，且给出的每个元素初值为1
vector<int>a(10,1);//用向量b给向量a赋值，a的值完全等价于b的值
vector<int>a(b);//将向量b中从0-2（共三个）的元素赋值给a，a的类型为int型
vector<int>a(b.begin(),b.begin+3);//从数组中获得初值
int b[7]={1,2,3,4,5,6,7};
vector<int> a(b,b+7）;

vector的常用内置函数使用

vector::begin/end

#include <iostream>
#include <vector>
using namespace std;
int main ()
{// vector::begin/endstd::vector<int> myvector;for (int i=1; i<=5; i++) myvector.push_back(i*2); //generate a vector[1,2,3,4,5]std::cout<<"size of vector is:\n"<<myvector.size()<<endl;std::cout<<"back of vector is:\n" <<myvector.back()<<endl;vector<int>::iterator v = myvector.begin()+1;//迭代器指向myvector的第二个元素std::cout<<"begin of vector is:\n" <<*v <<endl;//打印这个指针变量for (std::vector<int>::iterator it = myvector.begin() ; it < myvector.end(); it++)std::cout << ' ' << *it;std::cout << '\n';return 0;
}

output is:

size of vector is:
5
back of vector is:
10
begin of vector is:
42 4 6 8 10

// vector :: assign

std::vector<int> first;std::vector<int> second;std::vector<int> third;first.assign (7,100);             // 7 ints with a value of 100std::vector<int>::iterator it;it=first.begin()+1;second.assign (it,first.end()-1); // the 5 central values of firstint myints[] = {1776,7,4};third.assign (myints,myints+3);   // assigning from array.from 1776 to *1776 +3, three elementsstd::cout << "Size of first: " << int (first.size()) << '\n';for (std::vector<int>::iterator itf = first.begin() ; itf < first.end(); itf++){std::cout <<" "<<*itf;}std::cout<<endl;std::cout << "Size of second: " << int (second.size()) << '\n';for (std::vector<int>::iterator its = second.begin() ; its < second.end(); its++){std::cout <<" "<<*its;}std::cout<<endl;std::cout << "Size of third: " << int (third.size()) << '\n';for (std::vector<int>::iterator itt = third.begin() ; itt < third.end(); itt++){std::cout <<" "<<*itt;}std::cout<<endl;return 0;

output is:

Size of first: 7100 100 100 100 100 100 100
Size of second: 5100 100 100 100 100
Size of third: 31776 7 4

vector::at

at 和 operator[]具有一样的access elements 作用，但是at能够抛出out of range exception，所以推荐使用at,而不是运算符 [ ]

std::vector<int> myvector (4);   // 10 zero-initialized ints// assign some values:// or access some element;for (unsigned i=0; i<myvector.size(); i++)myvector.at(i)=i*i;std::cout << "myvector contains:";for (unsigned i=0; i<myvector.size(); i++)std::cout << ' ' << myvector.at(i);std::cout << '\n';return 0;

output is:

myvector contains: 0 1 4 9

vector::back

return the last element
myvector.back()

vector::size/capacity/max_size

size就是当前的vector长度，capacity是容器长度，一定是大于等于这个size的，当然当vector增长到capacity长度时不是说就塞不下了，capacity会继续allocate增大分配内存空间，而可以增大到的最大的理论极限就是max_size.

    std::vector<int> myvector;// set some content in the vector:for (int i=0; i<100; i++) myvector.push_back(i);std::cout << "size: " << (int) myvector.size() << '\n';std::cout << "capacity: " << (int) myvector.capacity() << '\n';std::cout << "max_size: " << (int) myvector.max_size() << '\n';return 0;

size: 100
capacity: 128
max_size: 1073741823

vector::vector::cbegin/cend

用于访问vector首尾元素，但无法修改该值

vector::clear

clear vector content

myvector.clear();

vector::data

指针指向vector首位

  std::vector<int> myvector (5);int* p = myvector.data();*p = 10;++p;*p = 20;p[2] = 100;std::cout << "myvector contains:";for (unsigned i=0; i<myvector.size(); ++i)std::cout << ' ' << myvector[i];std::cout << '\n';return 0;

output is:

myvector contains: 10 20 0 100 0

vector::empty

// Returns whether the vector is empty
//  (i.e. whether its size is 0).
myvector.empty()

vector::erase

  std::vector<int> myvector;// set some values (from 1 to 10)for (int i=1; i<=10; i++) myvector.push_back(i);// erase the 6th elementmyvector.erase (myvector.begin()+5);// erase the first 3 elements:myvector.erase (myvector.begin(),myvector.begin()+3);std::cout << "myvector contains:";for (unsigned i=0; i<myvector.size(); ++i)std::cout << ' ' << myvector[i];std::cout << '\n';return 0;

output is:

myvector contains: 4 5 7 8 9 10

vector:: front/back

// return the first and the last elements.
//unlike vector::begin/end, front/back returns direct reference.myvector.front()myvector.back()

vector::insert

//在a的第一个元素（从第0个算起）位置插入数值5,
a.insert(a.begin()+1,5);
//在a的第一个元素（从第0个算起）位置插入3个数，其值都为5
a.insert(a.begin()+1,3,5);
//b为数组，在a的第一个元素（从第0个元素算起）的位置插入b的第三个元素到第5个元素（不包括b+6）
a.insert(a.begin()+1,b+3,b+6);

   std::vector<int> myvector (3,100);//[100,100,100]std::vector<int>::iterator it;it = myvector.begin();it = myvector.insert ( it , 200 );[200,100,100,100]myvector.insert (it,2,300);[300,300,200,100,100,100]// "it" no longer valid, get a new one:it = myvector.begin();std::vector<int> anothervector (2,400);myvector.insert (it+2,anothervector.begin(),anothervector.end());//[300,300,400,400,200,100,100,1000]int myarray [] = { 501,502,503 };myvector.insert (myvector.begin(), myarray, myarray+3);//[501,502,503,300,300,400,400,200,100,100,100]std::cout << "myvector contains:";for (it=myvector.begin(); it<myvector.end(); it++)std::cout << ' ' << *it;std::cout << '\n';return 0;
}

output is:

myvector contains: 501 502 503 300 300 400 400 200 100 100 100

vector::pop_back/push_back

delete and add element at the end

vector::reserve

//increase vector capacity to n
myvector::reserve(n)

vector::resize

  std::vector<int> myvector;// set some initial content:for (int i=1;i<10;i++) myvector.push_back(i);myvector.resize(5);//[1,2,3,4,5]myvector.resize(8,100);//[1,2,3,4,5,100,100,100]myvector.resize(12);//[1,2,3,4,5,100,100,100,0,0,0,0]std::cout << "myvector contains:";for (int i=0;i<myvector.size();i++)std::cout << ' ' << myvector[i];std::cout << '\n';return 0;

output is:

myvector contains: 1 2 3 4 5 100 100 100 0 0 0 0

vector::shrink_to_fit

// shrink capacity to fit current vector size
myvector.shrink_to_fit()

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C++ vector库学习笔记

vector的初始化

vector的常用内置函数使用

vector::begin/end

// vector :: assign

vector::at

vector::back

vector::size/capacity/max_size

vector::vector::cbegin/cend

vector::clear

vector::data

vector::empty

vector::erase

vector:: front/back

vector::insert

vector::pop_back/push_back

vector::reserve

vector::resize

vector::shrink_to_fit

C++ vector库学习笔记相关推荐

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