STL Vector capacity

1、

#include <vector>
#include <iostream>
using namespace std;
void STLCapacity()
{
    vector<int> db(4);
    cout << db.empty() << endl;// Determine whether the object has elements , No element returns 1, Element returned 0.
    db.resize(3);// Reset the number of elements , The capacity size remains the same .
    db.reserve(10);//reserve(10) take db Capacity becomes 10, Only increase, not decrease 10 Be greater than db Its capacity .
    cout << db.size() << endl;// Number of elements .
    cout << db.capacity() << endl;//vector Capacity function of capacity() What you get is the size of the capacity .

    //vector<int> db1(5);// Object initialization is a few , The capacity is a few .
    //cout << db1.capacity() << endl;

    VS When the capacity in the version is insufficient , Add half of the existing capacity ,5+5/2==7. VC When the capacity in the version is insufficient , Double the existing capacity , namely 5*2.
    //db1.push_back(1);//6( data )==5+1>5( Capacity ), So add capacity , The capacity size becomes ：5+5/2==7.
    //cout << db1.capacity() << endl;
    //db1.push_back(1);//6+1( data )=7( Capacity ); The capacity can accommodate 7 individual , So the size remains the same .
    //db1.push_back(1);//8( data )==7+1>7( Capacity ), So add capacity , The capacity size becomes ：7+7/2==10.
    //cout << db1.capacity() << endl;
}

int main()
{
    STLCapacity();
    system("pause");
    return 0;
}
// Be careful ：reserve() And capacity() Function reallocates capacity , Iterative failure .