c++ 容器填充指定长度（fill_n）

#include <iostream>     // cout
#include <algorithm>    // fill_n
#include <vector>       // vector
using namespace std;
int main () {
    vector<int> myvector (,);        // myvector: 10 10 10 10 10 10 10 10

    fill_n (myvector.begin(),,);     //位置长度元素// myvector: 20 20 20 20 10 10 10 10
    fill_n (myvector.begin()+,,);   // myvector: 20 20 20 33 33 33 10 10

    cout << "myvector contains:";
    for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
        cout << ' ' << *it;
    cout << '\n';

    return ;
}