如何删除函数中创建的指针和返回值

Question

class AAA{
}

class BBB{
public:
   AAA* doSomething(){
      return new AAA();
   }
}

I created and returned a pointer with NEW in a function in class BBB, I want to know whether I should delete it somewhere. If I should, then how can I achieve that? I have some experience in Java, but I am a total newbie in C++, please help me.

Sorry, I think I did not describe my problem well. Suppose I have to write a function which concatenate two char[sizeA] and char[sizeB]. So I think I should do something like this:

char* concatenate(char* str1, char* str2, int sizeA, int sizeB){
   char* temp = new char[sizeA + sizeB - 1];
   ...
   return temp;
}

This is what I would do in Java, but I don't how to do it in C. I don't who is gonna use this returned char[] so I don't know where to write the "delect" code.

Answer 1

You don't need a pointer, so why use a pointer? What's wrong with

AAA doSomething()
{
   return AAA();
}

If you must, return a std::unique_ptr .

If you really want to use raw pointers, just delete the result.

Answer 2

The way to delete a pointer is using delete :

BBB b;
AAA *a = b.doSomething();

// ...

delete a;

But if you want make it safer use can use unique_ptr or shared_ptr .

However in C++ you don't have to new a variable as a pointer. You can create an object and return it:

class BBB{
public:
    AAA doSomething() { 
       return AAA();
    }
};

Answer 3

since your background is java. please read about parameter by value, by reference and by pointer.

AAA doSomething()
{
   return AAA();
}

you can create this function inside class B.

Answer 4

If you don't know who is going to use the pointer you created, the best way is to transfer the ownership of the pointer (and thus, the responsibility to delete it) to the client of your class.

There are several way to do so. The simplest one is to use std::auto_ptr . This way, the code using your function will gain the pointer ownership upon using your function and the destruction of the std::auto_ptr variable on the client code side will lead to the deletion of the pointer you created.