Lvalues and Rvalues (C++)

In C++, every expression is either an lvalue or an rvalue, describing how the expression can be used, not what it is.

Lvalue

• Refers to an object with an identifiable memory location (you can take its address with &).
• Can appear on the left-hand side of an assignment.

int x = 5; // 'x' is an lvalue
x = 10;    // Valid: 'x' can be assigned a new value

Rvalue

• A temporary value that does not persist beyond the expression.
• Can appear only on the right-hand side of an assignment.

int y = 5; // '5' is an rvalue
x = y + 1; // Valid: 'y + 1' is an rvalue

Purpose

Understanding these categories allows C++ to:

• Distinguish between copying and moving (via move semantics).
• Overload functions for lvalue and rvalue references

void f(const std::string& s); // takes lvalues
void f(std::string&& s);      // takes rvalues (temporary objects)

Note: && is an Rvalue Reference.