Member Avatar for joshilay

hi ...
can anyone please tell what are Lvalue and Rvalue errors in c and c++ ???

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Short answer: an lvalue names a storage location (something with an address you can usually assign to); an rvalue is a temporary value produced by an expression (a literal, the result of arithmetic, or a function returned by value) and typically cannot appear on the left side of =. As noted, putting a literal on the left triggers the common "lvalue required" complaint; ’s "location vs read" phrasing is a useful quick memory aid. is also right that compilers usually complain about lvalues — "rvalue required" messages are much rarer.

Common examples (valid vs invalid):

int a = 0;
(a + 1) = 5;         // error: (a+1) is not an lvalue
const int c = 3;
c = 4;               // error: c is an lvalue but not modifiable
int f();             // function returning by value
f() = 2;             // error: f() yields a temporary (rvalue), not assignable

C++ specifics: since C++11 the language added rvalue references and move semantics. std::move(x) produces an xvalue (an expiring value) that can bind to T&&, which lets you implement efficient moves — but it doesn’t make arbitrary expressions assignable. Example:

#include <utility>
int x = 1;
int&& r = std::move(x); // r binds to x's expiring value
r = 7;                  // OK: assignment goes through the reference (affects x)

Quick troubleshooting checklist:

  • Verify the left-hand expression is a modifiable lvalue (named variable or something returned by reference).
  • Don’t try to assign to literals, expressions like a+b, function returns by value, arrays, or functions.
  • If you must modify a temporary, store it in a named variable first or change the API to return a reference (T&) when appropriate.
  • For move-only semantics, use T&& and implement move constructors/assignments, and use std::move consciously.
  • Avoid removing const unsafely; fix the design instead.

These guidelines cover the usual causes of the errors you’re seeing and practical fixes that fit both C and modern C++.

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Member Avatar for Salem

Like 3 = myVariable; Will generate an lvalue error, because you can't assign to a numeric constant.

You can't assign to a function, or assign to an array either.

commented: Helps +1
Member Avatar for Grunt


I don't think you get rvalue required errors.

Member Avatar for ~s.o.s~


I don't think you get rvalue required errors.

Maybe he just wanted to know the difference between the L and R values ?

Member Avatar for himanjim

hi ...
can anyone please tell what are Lvalue and Rvalue errors in c and c++ ???

Lvalue means location value. And Rvalue means read value.
Suppose the code is
int i;
i=5;
here i is lvalue and 5 is Rvalue.
the code 5=i;
generates error lvalue required.

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