C++11 lvalue-to-rvalue conversion?

Question

I think I'm missing something basic regarding the lvalue-to-rvalue standard conversion.

From C++11 4.1:

A glvalue of a non-function, non-array type T can be converted to a prvalue

So we declare a variable x:

 int x = 42;

An expression x in this scope is now an lvalue (so also a glvalue). It satisfies the requirements in 4.1 for an lvalue-to-rvalue conversion.

What is a typical example of a context where the lvalue-to-rvalue conversion is applied to the expression x?

billz billz · Accepted Answer · 2013-07-14T04:21:47

A prvalue ("pure" rvalue) is an expression that identifies a temporary object (or a subobject thereof) or is a value not associated with any object.

struct Bar
{
    int foo()
    {
        int x = 42;
        return x;    // x is converted to prvalue
    }
};

the expression bar.foo() is a prvalue.

OR

Lambda expressions, such as

[](int x){return x*x;}

§ 3.10.1

A prvalue (“pure” rvalue) is an rvalue that is not an xvalue. [ Example: The result of calling a function whose return type is not a reference is a prvalue. The value of a literal such as 12, 7.3e5, or true is also a prvalue. —end example ]

see n3055.

C++11 lvalue-to-rvalue conversion?

1 Answers