When should you return by reference?

When should you return by reference?

Passing by reference means passing a reference to an object that already exist. Thus, if you want to return a reference in a function, it means that you must create that object in the function. You know that a function can create a new object in two ways: On the stack or the heap.

What happens if you return a reference?

The major difference is that the pointers can be operated on like adding values whereas references are just an alias for another variable. Functions in C++ can return a reference as it’s returns a pointer. When function returns a reference it means it returns a implicit pointer.

Can you return a reference?

A C++ function can return a reference in a similar way as it returns a pointer. When returning a reference, be careful that the object being referred to does not go out of scope. So it is not legal to return a reference to local var. But you can always return a reference on a static variable.

Why does copy assignment return a reference?

If you return a reference, minimal work is done. The values from one object are copied to another object. However, if you return by value for operator= , you will call a constructor AND destructor EACH time that the assignment operator is called!!

What does it mean to return a reference?

It means you return by reference, which is, at least in this case, probably not desired. It basically means the returned value is an alias to whatever you returned from the function. Unless it’s a persistent object it’s illegal.

Under what circumstances can you return a reference from a method?

Under what circumstances can you return a reference from a method? Only when it is safe to return, such as returning a reference from a method if the reference was passed into the method.

Is it good idea to return an address or a reference of a local variable?

The return statement should not return a pointer that has the address of a local variable ( sum ) because, as soon as the function exits, all local variables are destroyed and your pointer will be pointing to someplace in the memory that you no longer own.

Can we return a global variable by reference?

It can return the value of a global variable. That value will be an instantaneous copy, not a reference. That is to say when the global changes, the value will not change. Beyond that for all sorts of reasons the global variable should be avoided in the first instance.

Why pointer is not used in copy constructor?

Pointers are not included because the whole point of references is to “be” aliases for objects, whereas pointers represent indirection.

Why do we return references in operator overloading?

(This would also work (in most cases) if the operator returned a copy of the new value, but that’s generally less efficient.) We can’t return a reference from arithmetic operations, since they produce a new value. The only (sensible) way to return a new value is to return it by value.

How do you return a vector by reference?

You can’t return a reference anyway because the vector will get destroyed after the function ends, leaving an invalid reference. Returning a (const) reference makes more sense when the vector is stored somewhere so the vector stays alive after the function has returned.

What happens when you return a reference to a private variable?

Returning private members as reference is perfectly valid and the programmer who writes a class is responsible to carefully choose if this should be allowed. This link gives an example when this can be done. Means that the function returns a reference to an integer.

Why does the copy assignment operator return a reference?

If you return a reference, minimal work is done. The values from one object are copied to another object. However, if you return by value for operator=, you will call a constructor AND destructor EACH time that the assignment operator is called!!

Is it valid to return a copy of an object?

If you change the function declaration like this: then no copy will be made. However, in your specific case it would not be valid to return a reference to an object allocated on the stack. The problem is that the object would be destructed and invalidated before the caller had a chance to use it.

Why does the return statement always return a copy?

It will always return a copy. If you want to avoid the performance hit of copying the object on return, you can declare a pointer, build an instance of the object using new, and return the pointer. In that case, the pointer will be copied, but the object won’t be.

How to avoid copy on return in C + +?

However, if the object was passed to your function (directly or as a member of an object) you can safely return a reference to it and avoid copy-on-return. Finally, if you cannot trust copy elision and you want to avoid copies, you can use and return a unique_ptr instead of a reference.

https://www.youtube.com/watch?v=9WPUU9Uzaus