实战c++中的vector系列--vector<unique_ptr<>>赋值给vector<unique_ptr<>>

之前博客讲到 vector可以使用insert方法，将一个vector copy到另一个vector的后面。

之前的博客也讲到过，如果vector容器内部放的是unique_ptr是需要进行所有权转移的。

现在就来八一八如何vector<unique_ptr<>> insert to vector<unique_ptr<>>

如果常规的vector，我们就可以这么使用insert：

// inserting into a vector
#include <iostream>
#include <vector>

int main ()
{
  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  // "it" no longer valid, get a new one: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());
//now, 300 300 400 400 200 100 100 100
  int myarray [] = { 501,502,503 };
  myvector.insert (myvector.begin(), myarray, myarray+3);

  std::cout << "myvector contains:";
  for (it=myvector.begin(); it<myvector.end(); it++)
    std::cout << ‘ ‘ << *it;
  std::cout << ‘\n‘;

  return 0;
}
//输出：
501 502 503 300 300 400 400 200 100 100 100

但是对于vector内的unique point来说，就不能简单的使用普通迭代器了：需要使用对迭代器就行std::make_move_iterator操作：

看下英文描述最可靠：
A move_iterator is an iterator adaptor that adapts an iterator (it) so that dereferencing it produces rvalue references (as if std::move was applied), while all other operations behave the same.

就跟我们之前用到的std::move作用是一样一样的~
看看使用例子：

#include <iostream>     // std::cout
#include <iterator>     // std::make_move_iterator
#include <vector>       // std::vector
#include <string>       // std::string
#include <algorithm>    // std::copy

int main () {
  std::vector<std::string> foo (3);
  std::vector<std::string> bar {"one","two","three"};

  std::copy ( make_move_iterator(bar.begin()),
              make_move_iterator(bar.end()),
              foo.begin() );

  // bar now contains unspecified values; clear it:
  bar.clear();

  std::cout << "foo:";
  for (std::string& x : foo) std::cout << ‘ ‘ << x;
  std::cout << ‘\n‘;

  return 0;
}
//输出：
foo: one two three

接下来就是我们的使用了，简单了吧：

#include<iostream>
#include<vector>
#include <memory>
using namespace std;
void display_vector(vector<unique_ptr<int>> &vec);
int main()
{
    vector<unique_ptr<int>> vec;
    unique_ptr<int> s1(new int(1));
    unique_ptr<int> s2(new int(2));
    unique_ptr<int> s3(new int(3));
    unique_ptr<int> s4(new int(4));
    vec.push_back(std::move(s1));
    vec.push_back(std::move(s2));
    vec.push_back(std::move(s3));
    vec.push_back(std::move(s4));


    unique_ptr<int> s5(new int(5));
    vector<unique_ptr<int>> des_vec;
    des_vec.push_back(std::move(s5));
    des_vec.insert(des_vec.end(), std::make_move_iterator(vec.begin()), std::make_move_iterator(vec.end()));
    display_vector(des_vec);    
    cout << "now, des_vec size: " << des_vec.size() << endl;
    cout << "now, vec size: " << vec.size() << endl;

    return 0;
}

void display_vector(vector<unique_ptr<int>> &vec)
{
    for (auto it = vec.begin(); it != vec.end(); it++)
    {
        cout << **it << endl;
    }

//输出结果：
5
1
2
3
4
now, des_vec size: 5
now, vec size: 4