STL (2) container (under Vector)

vector constructor

Vector construction diagram:

Constructor:

vector<int>v1;//第一种
vector<int>v2(v1.begin(),v1.end());//第二种
vector<int>v3(10,100);//构造v3是10个100
vector<int>v4(v3);//拷贝构造

Vector assignment operation

vector<int>v2;
v2=v1;//v1是有值的vector

Vector capacity and size

insert and delete

Vector data access

for(i=0;i<v1.size();i++)//方法一
{
    
    
	cout<<v1[i];
}
for(i=0;i<v1.size();i++)//方法二
{
    
    
	cout<<v1.at(i);
}

Vector container calls

Function function:
realize the exchange of elements in two containers.

v1.swap(v2);//实现v1和v2元素互换。

Practical use:
clever use of swap can shrink the memory space;
if the capacity of v is 10000, but the actual element size is only 3;
first set the anonymous object x, the size of the anonymous object is the size of the actual element of v, after v and x are exchanged, the anonymous object will be The size is 10000, the actual size is 3, and the size and element of v are both 3. The anonymous object system will automatically recycle it for us, so there is no need to worry about wasting space.

Vector reserved space

Function: reduce the number of dynamic expansion.

v1.reserve(100);