The vector series in combat C + +-talk about the vector's insert () method (all Make_move_iterator)

Source: Internet
Author: User

As I said before about the insert () method of vectors, the elements of vector b are inserted into vector A, and we can imagine the results in vector a, but what about the elements in vector b?

Look at the program that you've written before:

#include <iostream>#include <vector>intMain () {STD:: vector<int>Myvector (3, -);STD:: vector<int>:: Iterator it;  it = Myvector.begin (); it = Myvector.insert (it, $); Myvector.insert (IT,2, -);//"It" no longer valid, get a new one:it = Myvector.begin ();STD:: vector<int>Anothervector (2, -); Myvector.insert (it+2, Anothervector.begin (), Anothervector.end ());intMyArray [] = {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;}

Now take care of something else: note how much of the vector is insert after insert:

#include <iostream>#include <vector>intMain () {STD:: vector<int>Myvector (3, -);STD:: vector<int>Anothervector (2, -);STD::cout<<"Before insert Myvector is:"; for(Autoit = Myvector.begin (); It<myvector.end (); it++)STD::cout<<"'<< *it;STD::cout<<STD:: Endl;STD::cout<<"Before insert Anothervector is:"; for(Autoit = 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(Autoit = Myvector.begin (); It<myvector.end (); it++)STD::cout<<"'<< *it;STD::cout<<STD:: Endl;STD::cout<<"Now the Anothervector is:"; for(Autoit = Anothervector.begin (); It<anothervector.end (); it++)STD::cout<<"'<< *it;STD::cout<<STD:: Endl;intMyarray[] = {501,502,503}; Myvector.insert (Myvector.begin (), myarray, MyArray +3);STD::cout<<After insert myarray[-Myvector, Myvector is: "; for(Autoit = Myvector.begin (); It<myvector.end (); it++)STD::cout<<"'<< *it;STD::cout<<STD:: Endl;STD::cout<<After insert myarray[-Myvector, myarray[] is: "; for(inti =0; I <3; i++) {STD::cout<<"'<< Myarray[i]; }return 0;}//output://before Insert Myvector is:100//before Insert Anothervector is:400//after Insert Myvector is:100//now the Anothervector is:400//after Insert myarray[] to Myvector, Myvector is:501 502 503//after Insert myarray[] to Myvector, myarray[] is:501 502 503

If you see this, you're sure to dozens in your heart, who cares about vector B, and VectOrb doesn't change.
Now it's time to get some curtailing, and put a smart pointer in the vector.

Previous blogs have also told you that the elements of vectors are smart pointers:

#include <iostream>#include <vector>#include <memory>using namespace STD;voidDisplay_vector ( vector<unique_ptr<int>> &vec);intMain () { 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(intI=0; I<vec.size (); i++) {cout<< *vec[i] <<" "; }return 0;}voidDisplay_vector ( vector<unique_ptr<int>> &vec) { for(Autoit = Vec.begin (); It! = Vec.end (); it++) {cout<< **it << Endl; }}

The above code crashes because VEC becomes invalid after VEC is insert, and we can't do anything to him ....

But it needs to be clear that this is not caused by insert, if copy will also cause this outcome, in fact, the culprit is make_move_iterator

Then look at the program:

#include <iostream>#include <list>#include <vector>#include <string>#include <iterator>intMain () {STD:: List<std::string>s{"One","both","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(AutoSTR:V1)STD::cout<<"\""<< Str <<"\" ";STD::cout<<"\nv2 now holds:"; for(AutoSTR:V2)STD::cout<<"\""<< Str <<"\" ";STD::cout<<"\noriginal list now holds:"; for(AutoSTR:S)STD::cout<<"\""<< Str <<"\" ";STD::cout<<' \ n ';}//output://v1 now holds: "One" "both" "Three "//v2 now holds: "One" "both" "Three "//original list now holds: ""

Last official procedure:

#include <iostream> //std::cout #include <iterator> //Std::make_move_iterator #include <vector> //std::vector #include <string> //std::string #include <algorithm> //std::copy intMain () {STD:: Vector<std::string>Foo3);STD:: Vector<std::string>bar{"One","both","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;}

* Need attention: *
* Bar.clear (); *
So at this point: bar now contains unspecified values; Clear it:

The vector series in combat C + +-talk about the vector's insert () method (all Make_move_iterator)

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