Updated Value Categories

In C++98/03, we had two basic categories of expressions:

• lvalue - an expression that can appear on the left-hand side of an assignment
• rvalue - an expression that can appear only on the right-hand side of an assignment

C++11 extended this taxonomy (due to the move semantics), with three more categories:

• xvalue - an eXpiring lvalue
• prvalue - a pure rvalue, an xvalue, a temporary object or subobject, or a value that is not associated with an object.
• glvalue - a generalised lvalue, which is an lvalue or an xvalue

Examples:

std::string str;
str;            // lvalue
42;             // prvalue
str + "10"      // prvalue
std::move(str); // xvalue

Let’s look at the Diagram

The tree chart below gives a better overview of the categories: