Can we return reference of local const variable C++

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since const variables are stored in read only memory. Can we return reference of const variable form function ?

Please suggest the answer.

int& fun()
{
    int a = 10;
    const int b = a;
    return b;
}

Also please help me with memory lay out of C++ program where does const values are stored. Where read only data are present ?

"since const variables are stored in read only memory" - that is not correct. And the nswer is "no", you cannot safely return a reference to a local varible - const or not. The variable is destroyed when you return from the function and the reference is then no longer valid.

7.4a, As with pass by value, you can return by value literals (e.g. 5), variables (e.g. x), try to return the address of a variable local to the function, your program will exhibit In case C, we're trying to initialize const reference cref with the copy of the  Return by reference. Similar to pass by address, values returned by reference must be variables (you should not return a reference to a literal or an expression that resolves to a temporary value, as those will go out of scope at the end of the function and you’ll end up returning a dangling reference).

Why can't you return a local variable by reference?, How do I call a variable from one class into another in C#?. 40,502 Views So, you can return reference to a local variable if the receiver is a const. 4.4k views  The qualifier const can be applied to the declaration of any variable to specify that its value will not be changed ( Which depends upon where const variables are stored, we may change the value of const variable by using pointer ). The result is implementation-defined if an attempt is made to change a const. 1) Pointer to variable.

Storage classes of a variable defines existence of variable in program during execution. In your example scope of variable is only with in function and storage class type of auto. Any reference to variable outside the scope of function will be invalid.

How to modify a const variable in C?, Any attempt to modify this read-only variable will then result in a compilation error​: int main(). {. const int var = 10;. var = 15;. printf ( "var = %d\n" , var);. return 0;. } That is why we are able to change the value of a constant variable through a ways to use Const with Reference to a Pointer in C++ · Function overloading and​  const (C# Reference) You use the const keyword to declare a constant field or a constant local. Constant fields and locals aren't variables and may not be modified. Constants can be numbers, Boolean values, strings, or a null reference.

If you want to return the variable as a reference, then please make the variable has "static" , since it is stored globally.

References in C++, References in C++ A variable can be declared as reference by putting '&' in the declaration. object by using reference. for ( const auto &x : vect). cout << x << endl;. return 0;. } chevron_right. filter_none. References vs Pointers Both references and pointers can be used to change local variables of one function inside  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. Despite above similarities, there are following differences between references and pointers.

Returning values by reference in C++, Returning values by reference in C++ - A C++ program can be made easier to read and maintain by using A C++ function can return a reference in a similar way as it re. Returning values by reference in C++ So it is not legal to return a reference to local var. But you can always return a reference on a static variable​. Starting with C# 7.0, C# supports reference return values (ref returns). A reference return value allows a method to return a reference to a variable, rather than a value, back to a caller. The caller can then choose to treat the returned variable as if it were returned by value or by reference. The caller can create a new variable that is

Effective C++, For any variable, declare it as const unless you need to modify its value. When you don't declare, C++ compiler will implicitly declare its own default Never return reference to a local static object (incorrect behavior with multiple accesses)​. References used as function parameters can also be const. This allows us to access the argument without making a copy of it, while guaranteeing that the function will not change the value being referenced. // ref is a const reference to the argument passed in, not a copy. void changeN(const int &ref) ref = 6; // not allowed, ref is const.

C++ Core Guidelines, Violations of rules will be flagged with references (or links) to the This is a set of core guidelines for modern C++ (currently C++17) It is easier to reason about constants than about variables. If a class X has a public static function that contains a function-local static of the class' type X and returns a  Changing Value of a const variable through pointer. The variables declared using const keyword, get stored in .rodata segment, but we can still access the variable through the pointer and change the value of that variable. By assigning the address of the variable to a non-constant pointer, We are casting a constant variable to a non-constant pointer.

Comments
  • Well, you can certainly return the reference. That's perfectly valid. What's not valid is using the referenced object.