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 it = myvector.insert ( it , 200 );//200 100 100 100  myvector.insert (it,2,300);//300 300 200 100 100 100  // "it" no longer valid, get a new one:  it = myvector.begin();  std::vector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::copyint 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：51234now, des_vec size: 5now, vec size: 4