之前说过了关于vector的insert()方法，把vector B的元素插入到vector A中。vector A中的结果我们可想而知，可是vector B中的元素还会怎样？
看看之前写过的程序：
#include <iostream>
#include <vector>
int main ()
{
std::vector<int> myvector (3,100);
std::vector<int>::iterator it;
it = myvector.begin();
it = myvector.insert ( it , 200 );
myvector.insert (it,2,300);
// "it" no longer valid, get a new one: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());
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;
}如今关心一下别的：注意是insert后，被insert的vector为多少了：
#include <iostream>
#include <vector>
int main()
{
std::vector<int> myvector(3, 100);
std::vector<int> anothervector(2, 400);
std::cout << "Before insert myvector is:";
for (auto it = myvector.begin(); it<myvector.end(); it++)
std::cout << ' ' << *it;
std::cout << std::endl;
std::cout << "Before insert anothervector is:";
for (auto it = anothervector.begin(); it<anothervector.end(); it++)
std::cout << ' ' << *it;
std::cout << std::endl;
myvector.insert(myvector.end(), anothervector.begin(), anothervector.end());
std::cout << "After insert myvector is:";
for (auto it = myvector.begin(); it<myvector.end(); it++)
std::cout << ' ' << *it;
std::cout << std::endl;
std::cout << "Now the anothervector is:";
for (auto it = anothervector.begin(); it<anothervector.end(); it++)
std::cout << ' ' << *it;
std::cout << std::endl;
int myarray[] = { 501,502,503 };
myvector.insert(myvector.begin(), myarray, myarray + 3);
std::cout << "After insert myarray[] to myvector, myvector is:";
for (auto it = myvector.begin(); it<myvector.end(); it++)
std::cout << ' ' << *it;
std::cout << std::endl;
std::cout << "After insert myarray[] to myvector, myarray[] is:";
for (int i = 0; i < 3; i++)
{
std::cout << ' ' << myarray[i];
}
return 0;
}
//输出：
//Before insert myvector is : 100 100 100
//Before insert anothervector is : 400 400
//After insert myvector is : 100 100 100 400 400
//Now the anothervector is : 400 400
//After insert myarray[] to myvector, myvector is : 501 502 503 100 100 100 400 400
//After insert myarray[] to myvector, myarray[] is : 501 502 503假设你看到此时，你肯定会在心里骂娘，谁还关心vector B，而且vectorB并没有变化。
如今是时候来点猛药了。vector中放智能指针。
之前博客也讲诉过对于vector的元素为智能指针的时候：
#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;
//display_vector(vec);
cout << "now, vec size: " << vec.size() << endl;
for (int i=0; i<vec.size(); i++)
{
cout << *vec[i] << " ";
}
return 0;
}
void display_vector(vector<unique_ptr<int>> &vec)
{
for (auto it = vec.begin(); it != vec.end(); it++)
{
cout << **it << endl;
}
}上面代码会崩溃。原因就是vec被insert后 。vec变得无效了，我们不能对他做什么。。。。。
可是须要明白的是这不是insert造成的，假设copy也会造成这一的结局，事实上罪魁祸首就是make_move_iterator
再看程序：
#include <iostream>
#include <list>
#include <vector>
#include <string>
#include <iterator>
int main()
{
std::list<std::string> s{ "one", "two", "three" };
std::vector<std::string> v1(s.begin(), s.end()); // copy
std::vector<std::string> v2(std::make_move_iterator(s.begin()),
std::make_move_iterator(s.end())); // move
std::cout << "v1 now holds: ";
for (auto str : v1)
std::cout << "\"" << str << "\" ";
std::cout << "\nv2 now holds: ";
for (auto str : v2)
std::cout << "\"" << str << "\" ";
std::cout << "\noriginal list now holds: ";
for (auto str : s)
std::cout << "\"" << str << "\" ";
std::cout << '\n';
}
//输出：
//v1 now holds : "one" "two" "three"
//v2 now holds : "one" "two" "three"
//original list now holds : ""最后再上一个官方程序：
#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;
}* 须要注意：*
* bar.clear();*
因此此时: bar now contains unspecified values; clear it: