An object is a contiguous region of memory storage. An lvalue (pronounced: L value) is an expression that refers to such an object. The original definition of lvalue referred to "an object that can appear on the left-hand side of an assignment." However, const objects are lvalues, and yet they cannot appear on the left-hand side of an assignment. An expression that can appear in the right-hand side of an expression (but not in the left-hand side of an expression) is an rvalue. For example:
#include <string>
using namespace std;
int& f();
void func()
{
int n;
char buf[3];
n = 5; // n is an lvalue; 5 is an rvalue
buf[0] = 'a'; //buf[0] is an lvalue, 'a' is an rvalue
string s1 = "a", s2 = "b", s3 = "c"; // "a", "b", "c" are rvalues
s1 = // lvalue
s2 +s3; //s2 and s3 are lvalues that are implicitly converted to rvalues
s1 =
string("z"); // temporaries are rvalues
int * p = new int; // p is an lvalue; 'new int' is an rvalue
f() = 0; // a function call that returns a reference is an lvalue
s1.size(); // otherwise, a function call is an rvalue expression
}
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