lvalue

An lvalue, short for locator value, is an expression that designates a memory location where an object resides. In languages such as C and C++, an lvalue refers to an object with identifiable storage, enabling you to read from or, provided the object is not const, modify its contents. The concept is tied to the idea that the expression has a persistent location in memory.

An expression is an lvalue if it can appear on the left-hand side of an assignment. When an lvalue is used in a context that requires just a value, the language performs an lvalue-to-rvalue conversion to obtain the object’s current value, producing an rvalue. Conversely, rvalues denote values that do not have a persistent storage location. Not all expressions are lvalues; for example, many arithmetic expressions yield rvalues, and certain results of function calls may also be non-lvalues depending on the language.

In practice, lvalues can be variables, elements of arrays, or dereferenced pointers, as long as the object they designate is modifiable (unless it is declared const). The address-of operator & can be applied to an lvalue to obtain a pointer to its storage. Some expressions that designate storage may be non-modifiable, such as const objects or certain array categories, in which case they are lvalues but not assignable.

In modern C++, the language distinguishes between glvalues (generalized lvalues), prvalues, and xvalues, with lvalues corresponding to glvalues. Many discussions still use lvalue as a shorthand for glvalue, particularly when addressing left-hand side semantics. See also rvalue.