CODEWITHSUNDEEP
c++11
Elio
Elio

Reputation: 130

Returning lvalue reference causes a closure?

I'm learning about lvalue/rvalue and there is an example about lvalue:

int& foo();
foo() = 42; // ok, foo() is an lvalue

Normally people will let foo() return a global variable or a static varible inside its body, but if we define a local variable inside foo's body, it also works (with warning: reference to stack memory associated with local variable 'i' returned [-Wreturn-stack-address]):

#include <iostream>
using namespace std;

int &foo(){int i=7; return i;};

int main() {

    foo() = 42;
    return 0;
}

Why this is allowed in C++, is it a closure?

Upvotes: 0

Views: 34

Answers (1)

Igor Tandetnik
Igor Tandetnik

Reputation: 52471

This program exhibits undefined behavior, by way of accessing an object after its lifetime has ended.

It's pointless to return a reference to a local variable - any use of such a reference by the caller is undefined, since the local variable is necessarily destroyed by that time.

Upvotes: 2

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