Several cases about function return value

in the interior of a function, return returns a copy, whether the variable, object, or pointer is a copy, but the copy is a shallow copy.

1. If a variable of a basic type is returned, for example:

int a;a = 5;return A

  then a5 return, then aa was destroyed, but its copy 5 or successfully returned, so there's no problem with that.

2. But for non-dynamic allocation (NEW/MALLOC) pointers, like 1, There are problems, such as inside a function:

int a[] = {1, 2};return A;

Then the pointer is also returnedAa0x002345fc0x2345fc is able to return successfully. When return After the completion of the execution, a0x002345fc0x002345fc

3. Another case of returning ( dynamically assigned ) pointers, such as inside a function:

int a = new int (5); return A;

It is possible to do so. when return a is executed,a is not destroyed (must be deleted to destroy a), so the A returned here is valid.

4. If it is not a basic data type, such as:

Class A{public:               Otherclass * ...};

If there is a class A local variable inside a function , such as:

A A;return A;

A copy of A is also returned , and if a does not have a deep copy constructor, it will call the default copy constructor ( shallow copy ), which will fail;

This is possible if a deep copy constructor is provided in a.

The experiment code is as follows:

#include <iostream>using namespace Std;int some_fun1 () {int a = 5;return A;                   ok}int* some_fun2 () {int a = 5;int *b = &a;return b;                   Not ok}int* some_fun3 () {int *c = new int (5); return C; OK, return C is not destroyed after execution (must use Delete to destroy)}class csomething{public:int a;int b;public:csomething (int a, int b) {this-> A = A; This->b = b;}};            Class ca{private:csomething* sth; Member Variable PUBLIC:CA (csomething* sth) {this->sth = new csomething (Sth->a, sth->b) in the form of pointers;} If you do not implement a deep copy, note this copy constructor CA (ca& obj) {sth = new csomething ((Obj.sth)->a, (obj.sth)->b);} ~ca () {cout << "in the destructor of class CA ..." << endl;if (NULL! = sth) delete sth;} void Show () {cout << ("<< sth->a <<", "<< sth->b <<") "<< Endl;} void SetValue (int a, int b) {sth->a = A;sth->b = b;} void Getsthaddress () {cout << sth << Endl;}}; CA some_fun4 () {csomething C (1, 2); CA a (&c); RetuRN A;              If the CA does not implement a deep copy, then not OK, if deep copy is implemented, then ok}int main (int argc, char* argv[]) {int a = SOME_FUN1 (); cout << a << Endl;             Okint *b = some_fun2 () cout << *b << Endl;           Not OK, even if the return result is correct, it is just luck good int *c = SOME_FUN3 ();             OK, when return C is executed, C is not destroyed (you must use Delete to destroy) cout << *c << endl;delete c;ca d = some_fun4 (); Not OK If the CA does not implement a deep copy, or okd.show () If deep copy is implemented; return 0;}

Several cases about function return value