Table of Contents
- 1 Why is it unsafe for a function to return a local variable by reference?
- 2 Can we return local variable by reference?
- 3 How do you use reference variables in C++?
- 4 What happens if we return address of a local variable?
- 5 When a function call returns what happens to variables in the local scope?
- 6 How does a function return values?
- 7 Why reference variable is used in C++?
- 8 Why reference is used in C++?
- 9 What happens when you return a variable from a function?
- 10 Can you return a variable by reference in C?
- 11 What happens when a variable goes out of scope at end?
Why is it unsafe for a function to return a local variable by reference?
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 local variable by reference?
If you return it by reference, you are returning an alias to that same variable. If you pass it to another method by reference, you are passing a reference to the variable it aliases. When you make a ref local alias, you make a new alias to the same variable.
How do you reference a local variable?
Reference Variables
- A reference variable is a nickname, or alias, for some other variable.
- To delare a reference variable, we use the unary operator & int n = 5; // this declares a variable, n int & r = n; // this declares r as a reference to n.
- To declare a reference variable, add the & operator after the type.
How do you use reference variables in C++?
Once a reference is initialized with a variable, either the variable name or the reference name may be used to refer to the variable….Creating References in C++
Sr.No | Concept & Description |
---|---|
1 | References as Parameters C++ supports passing references as function parameter more safely than parameters. |
What happens if we return address of a local variable?
Once the function returns it does not exist anymore and hence you should not return the address of a local variable. In other words the lifetime of a is within the scope( { , } ) of the function and if you return a pointer to it what you have is a pointer pointing to some memory which is not valid.
Can a function return a reference?
Functions can be declared to return a reference type. There are two reasons to make such a declaration: The information being returned is a large enough object that returning a reference is more efficient than returning a copy.
When a function call returns what happens to variables in the local scope?
A local variable retains its value until the next time the function is called A local variable becomes undefined after the function call completes The local variable can be used outside the function any time after the function call completes.
How does a function return values?
A function defined with a return type must include an expression containing the value to be returned. In this example, the return statement initializes a variable of the returned type. The variable answer is initialized with the int value 30. The type of the returned expression is checked against the returned type.
Can a function return an address?
Because return by address just copies an address from the function to the caller, return by address is fast. This works because dynamically allocated memory is not destroyed at the end of the block in which it is allocated, so that memory will still exist when the address is returned back to the caller.
Why reference variable is used in C++?
C++ introduces a new kind of variable known as Reference Variable. It provides an alias (alternative name) for a previously defined variable. A reference variable must be initialized at the time of declaration. This establishes the correspondences between the reference and the data onject which it name.
Why reference is used in C++?
Both references and pointers can be used to change local variables of one function inside another function. Both of them can also be used to save copying of big objects when passed as arguments to functions or returned from functions, to get efficiency gain.
What happens to a local variable when a function call completes?
When the execution of the function terminates (returns), the local variables are destroyed. So it is not possible for a function to set some local variable to a value, complete its execution, and then when it is called again next time, recover the local variable.
What happens when you return a variable from a function?
Upon leaving a function, all local variables are destroyed. By returning a reference to tmp, you are returning a reference to an object that soon ceases to exist (that is, technically, the address of a memory region whose contents are no longer meaningful).
Can you return a variable by reference in C?
However, just like return by address, you should not return local variables by reference. Consider the following example: In the above program, the program is returning a reference to a value that will be destroyed when the function returns. This would mean the caller receives a reference to garbage.
Why can’t we return the address of a local variable?
a is an array local to the function.Once the function returns it does not exist anymore and hence you should not return the address of a local variable. In other words the lifetime of a is within the scope ({, }) of the function and if you return a pointer to it what you have is a pointer pointing to some memory which is not valid.
What happens when a variable goes out of scope at end?
Because the variables are evaluated before the function returns, and a copy of the value is returned to the caller, there are no problems when the function’s variable goes out of scope at the end of the function.