Smart pointers for C + + (2)

weak_ptr Example

/*The main reason for using shred_ptr is to avoid focusing on the resource that the pointer is pointing to//only the pointer will automatically release related resources to objects that are no longer needed//But in some cases, this is not what we need. For example, a circular reference. Two objects all refer to each other. or share an object but do not occupy the object//This time can use weak_ptr in fact relative shared_ptr the pointer does not increase the count//*/#include<iostream>#include<string>#include<vector>#include<memory>using namespacestd;classperson{ Public:    stringname; shared_ptr<Person>mother; shared_ptr<Person>father; Vector<shared_ptr<Person>>Kids; Person (Const string&N, shared_ptr<Person> m =nullptr, shared_ptr<Person> f =nullptr): Name (n), mother (M), Father (f) {}~Person () {cout<<"Delete"<< name <<Endl; }};shared_ptr<Person> initfamily (Const string&name) {shared_ptr<Person> Mom (NewPerson (name +"' s mom")); shared_ptr<Person> Dad (NewPerson (name +"' s dad")); shared_ptr<Person> Kid (NewPerson (Name,mom,dad)); Mom-Kids.push_back (Kid); Dad-Kids.push_back (Kid); returnKid;}int_tmain (intARGC, _tchar*argv[]) {shared_ptr<Person> p = initfamily ("Nico"); cout<<"Nico ' s family exists"<<Endl; cout<<"-Nico is shared"<< P.use_count () <<" Times"<<Endl; cout<<"-Name of 1st Kid of Nico ' s mom:"<< p->mother->kids[0]->name <<Endl; P= Initfamily ("Jim"); cout<<"Jim ' s family exists"<<Endl;    return 0;}

The result of running the code is as follows:

Nico ' s family exists
-Nico is shared 3 times
-Name of 1st Kid of Nico ' s Mom:nico
Jim ' s family exists
Please press any key to continue ...

We don't actually see the pointer pointing to the release of the resource because the shared_ptr pointer is used in the vector in class person to increase the count of resources, so it's not released in time.

We should change the vector to weak_ptr and use the lock () function to promote the weak_ptr to shared_ptr.

/*The main reason for using shred_ptr is to avoid focusing on the resource that the pointer is pointing to//only the pointer will automatically release related resources to objects that are no longer needed//But in some cases, this is not what we need. For example, a circular reference. Two objects all refer to each other. or share an object but do not occupy the object//This time can use weak_ptr in fact relative shared_ptr the pointer does not increase the count//*/#include<iostream>#include<string>#include<vector>#include<memory>using namespacestd;classPerson { Public:    stringname; shared_ptr<Person>mother; shared_ptr<Person>father; Vector<weak_ptr<Person>> Kids;//weakpointer!!!Person (Const string&N, shared_ptr<Person> m =nullptr, shared_ptr<Person> f =nullptr): Name (n), mother (M), Father (f) {}~Person () {cout<<"Delete"<< name <<Endl; }};shared_ptr<Person> initfamily (Const string&name) {shared_ptr<Person> Mom (NewPerson (name +"' s mom")); shared_ptr<Person> Dad (NewPerson (name +"' s dad")); shared_ptr<Person> Kid (NewPerson (Name,mom,dad)); Mom-Kids.push_back (Kid); Dad-Kids.push_back (Kid); returnKid;}int_tmain (intARGC, _tchar*argv[]) {shared_ptr<Person> p = initfamily ("Nico"); cout<<"Nico ' s family exists"<<Endl; cout<<"-Nico is shared"<< P.use_count () <<" Times"<<Endl; cout<<"-Name of 1st Kid of Nico ' s mom:"<< p->mother->kids[0].Lock()->name <<Endl; P= Initfamily ("Jim"); cout<<"Jim ' s family exists"<<Endl; return 0;}

The operation results are as follows

Nico ' s family exists
-Nico is shared 1 times
-Name of 1st Kid of Nico ' s Mom:nico
Delete Nico
Delete Nico ' s dad
Delete Nico ' s mom
Jim ' s family exists
Delete Jim
Delete Jim ' s dad
Delete Jim ' s mom
Please press any key to continue ...

You can see that the resource is released correctly

Code adapted from C + + standard library-Self-study tutorial and Reference Manual English second Edition

Smart pointers for C + + (2)