vector結構
start指向這塊空間的起始位置
finish指向有效元素的後一個位置
end_of_storage指向這塊空間的下一個位置
vector的迭代器
vector迭代器的底層其實就是一個原生指針,對迭代器的 ++ 等同於對指針做 ++ 操作,對迭代器的解引用 (*) 等同於對原生指針解引用,取其內容.
vector迭代器的操作(圖片截取自cplusplus):
這裏演示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;
}
運行結果:
vector的成員函數
(圖片截取自cplusplus)
- 驗證vector的構造函數
void test_constructor()
{
//1.直接構造一個空的順序表
vector<int> v1;
cout<<"v1.size() = "<<v1.size()<<endl;
cout<<"v1.capacity() = "<<v1.capacity()<<endl;
//2.構造一個空的順序表,但是空間大小設置爲20
vector<int> v2(20);
cout<<"v2.size() = "<<v2.size()<<endl;
cout<<"v2.capacity() = "<<v2.capacity()<<endl;
//3.構造一個arr對象,並使用arr對vector進行初始化
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.構造一個vector,期中有4個值爲100的元素
vector<int> v4(4,10);
cout<<"v4.size() = "<<v4.size()<<endl;
cout<<"v4.capacity() = "<<v4.capacity()<<endl;
PrintVector(v4);
}
運行結果:
由此可見,構建vector可以是一個空的vector,也可以用一塊固定長度空間,也可以對這塊空間初始化.
常用接口介紹
- push_back,pop_back,erase,insert
這四個接口的用法很簡單,有過一些數據結構基礎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個元素"<<endl;
PrintVector(v);
v.pop_back();
v.pop_back();
cout<<"尾刪兩個元素"<<endl;
PrintVector(v);
cout<<"在最前面插入0"<<endl;
v.insert(v.begin(),0);
PrintVector(v);
cout<<"刪除最前面的0"<<endl;
v.erase(v.begin());
PrintVector(v);
}
運行結果:
push_back和pop_back都很好理解,我們重點看一下erase和insert(圖片截取自cplusplus)
我們可以看到,erase和insert都是配合迭代器使用的.兩個函數不僅可以刪除一個值,也可以刪除一段區間.
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個0"<<endl;
v.insert(v.begin(),5,0);
PrintVector(v);
cout<<"刪除起始位置的5個值"<<endl;
v.erase(v.begin(),v.begin()+5);
PrintVector(v);
}
結果演示:
- clear,assign
首先看一下clear和assign的用法(圖片截取自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;
}
結果演示:
由結果可以看出,clear清除vector,只清除有效區間,也就是將 finish置爲start,但是不清除空間,也就是 end_of_storage 不改變
assign總結: assign(m,n)是置m個n值
當m的大小小於capacity時,會將這段空間的有效區間(size)置爲m,並且將值都改爲n
當m的大小大於capacity時,會將size和capacity都修改爲m,並且賦值爲n
assign也可以用一段空間來修改
- reserve,resize
reserve : 主要用於當你已知自己將需要多大的空間時,就預先開好,避免在插入數據時擴容,可以提高效率.reserve只預先開好capacity
resize : 主要用於當你已知自己需要的有效空間的大小,可以預先開好空間,並且初始化.resize會預先開好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;
}
運行結果:
觀察結果我們可以看出,reserve只開空間,當開的空間比當前空間小的時候,並不改變空間大小.
resize(m,n),當m比當前空間小的時候,會將有效空間修改爲m,當m比當前空間大的時候,會將size和capacity置爲m
整體代碼
#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.直接構造一個空的順序表
vector<int> v1;
cout<<"v1.size() = "<<v1.size()<<endl;
cout<<"v1.capacity() = "<<v1.capacity()<<endl;
//2.構造一個空的順序表,但是空間大小設置爲20
vector<int> v2(20);
cout<<"v2.size() = "<<v2.size()<<endl;
cout<<"v2.capacity() = "<<v2.capacity()<<endl;
//3.構造一個arr對象,並使用arr對vector進行初始化
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.構造一個vector,期中有4個值爲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個元素"<<endl;
PrintVector(v);
v.pop_back();
v.pop_back();
cout<<"尾刪兩個元素"<<endl;
PrintVector(v);
cout<<"在最前面插入0"<<endl;
v.insert(v.begin(),0);
PrintVector(v);
cout<<"刪除最前面的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個0"<<endl;
v.insert(v.begin(),5,0);
PrintVector(v);
cout<<"刪除起始位置的5個值"<<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;
}
