Do rvalue references allow dangling references? If you meant “Is it possible to create dangling rvalue references” then the answer is yes. Your example, however, string middle_name () { return “Jaan”; } int main() { string&& nodanger = middle_name(); // OK. // The life-time of the temporary is extended // to the life-time of the … Read more
Every expression is one, and only one, of: lvalue xvalue prvalue The union of expressions that are lvalues and xvalues are known collectively as glvalues. The union of expressions that are xvalues and prvalues are known collectively as rvalues. Thus xvalue expressions are known both as glvalues and rvalues. The handy diagram found in Alf‘s … Read more
The committee already seems to be aware that there’s a problem in this part of the standard. CWG issue 690 talks about a somewhat similar problem with exactly the same part of the standard (in the “additional note” from September, 2009). I’d guess new language will be drafted for that part of the standard soon. … Read more
string literals are lvalues, but you can’t change them rvalue, but if it’s a pointer and non-NULL, the object it points to is an lvalue The C standard recognizes the original terms stood for left and right as in L = R; however, it says to think of lvalue as locator value, which roughly means … Read more
The word “shall” in the standard language means a strict requirement. So, yes, your code is ill-formed (it is an error) because it attempts to apply address-of operator to a non-lvalue. However, the problem here is not an attempt of taking address of a temporary. The problem is, again, taking address of a non-lvalue. Temporary … Read more
That is a known issue/feature of the VS compilers. They have always allowed that and there does not seem to be any push into removing that extension.
The things that are automatically treated as rvalues are things without names, and things that (very shortly) will not have a name (in the return value case). T&& t has a name, it is t. The reason why rvalues are those things is that referring to them after that point of use is next to … Read more
Other people have tackled the functional difference between post and pre increment. As far as being an lvalue is concerned, i++ can’t be assigned to because it doesn’t refer to a variable. It refers to a calculated value. In terms of assignment, both of the following make no sense in the same sort of way: … Read more
Is bar an rvalue or an lvalue? The question answers itself. Whatever has a name is an lvalue(1). So bar is an lvalue. Its type is “rvalue reference to string“, but it’s an lvalue of that type. If you want to treat it as an rvalue, you need to apply std::move() to it. If you … Read more