In practice, the vector series in c ++ -- let's talk about the insert () method of the vector (all of which are caused by make_move_iterator)

In practice, the vector series in c ++ -- let's talk about the insert () method of the vector (all of which are caused by make_move_iterator)

I have mentioned the insert () method of vector before and insert the element of vector B into vector A. we can imagine the results in vector A, but what about the elements in vector B?

Check out the previously written programs:

#include 
  
   #include 
   
    int main (){  std::vector
    
      myvector (3,100);  std::vector
     
      ::iterator it;  it = myvector.begin();  it = myvector.insert ( it , 200 );  myvector.insert (it,2,300);  // "it" no longer valid, get a new one:  it = myvector.begin();  std::vector
      
        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
       
      
     
    
   
  

If you see that at this time, you will surely swear at it, who cares about vector B, and vectorB has not changed.
Now it's time to take a try. Put the smart pointer in the vector.

Previously, my blog mentioned that when the element of a vector is a smart pointer:

#include  #include  #include  using namespace std;void display_vector(vector  > &vec);int main(){ vector  > vec; unique_ptr  s1(new int(1)); unique_ptr  s2(new int(2)); unique_ptr  s3(new int(3)); unique_ptr  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  s5(new int(5)); vector  > 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){ for (auto it = vec.begin(); it != vec.end(); it++) { cout << **it << endl; }}            

The code above will crash because after vec is inserted, vec becomes invalid and we cannot do anything to it .....

But it should be clear that this is not caused by insert. If copy will also cause this ending, the culprit isMake_move_iterator

Check the program again:

# Include  # Include  # Include  # Include  # Include  Int main () {std: list  S {"one", "two", "three"}; std: vector  V1 (s. begin (), s. end (); // copy std: vector  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';} // output: // v1 now holds: "one" "two" "three" // v2 now holds: "one" "two" "three" // original list now holds :""        

Finally, go to an official program:

#include  // std::cout#include  // std::make_move_iterator#include  // std::vector#include  // std::string#include // std::copyint main() { std::vector  foo(3); std::vector  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;}      

* Note :*
* Bar. clear ();*
So now: bar now contains unspecified values; clear it: