那么对于（a=2）=66这样的表达式怎么看?另外，为什么自增（减）运算只能用于左值，不能用于右值，即表达式++（a++）为什么错误呢？  回复  更多评论
  

@wu
（a=2）=66 中就是按顺序赋值就是了 所以a=66

++（a++）
至于右值为什么不能用，因为后增量(后减量)返回的值是修改前的变量值，故不为左值，所以他就不能用了  回复  更多评论
  

++（a++）
a++相当于
int a;
{
int temp=a;
a++;
teturn temp;
}
所以我们可以将++(a++)看成++temp;而temp
显然是一个右值，所以不能用啊~~  回复  更多评论
  

错了，没有什么左值和右值！
翻译害人不浅，
L-value中的L指的是Location，表示可寻址。The "l" in lvalue can be though of as location
R-value中的R指的是Read，表示可读。The "r" in rvalue can be thought of as "read" value.  回复  更多评论
  

原创好文章，谢谢楼主。  回复  更多评论
  

From Wikipedia, the free encyclopedia
Jump to: navigation, search
L-value or L value may refer to:

A value (computer science) that has an address
The value assigned to an L-shell, a particular set of planetary magnetic field lines
A measure of brightness of a lunar eclipse on the Danjon scale

From Wikipedia, the free encyclopedia
Jump to: navigation, search
R-value can refer to:

Properties of materials:
R-value (insulation), the efficiency of insulation
R-value (soils), stability of soils and aggregates for pavement construction
r-value, in computer science, a value that does not have an address in a computer language
R-factor (crystallography), a measure of the agreement between the crystallographic model and the diffraction data
In statistics, r (or r value) refers to the Pearson product-moment correlation coefficient, often called simply correlation coefficient

翻译不对,谢谢  回复  更多评论
  

这是<C++ primmer>中的一部分：

Lvalues and Rvalues
左值和右值
We'll have more to say about expressions in Chapter 5, but for now it is useful to know that there are two kinds of expressions in C++:

我们在第五章再详细探讨表达式，现在先介绍 C++ 的两种表达式：

lvalue (pronounced "ell-value"): An expression that is an lvalue may appear as either the left-hand or right-hand side of an assignment.

左值（发音为 ell-value）：左值可以出现在赋值语句的左边或右边。

rvalue (pronounced "are-value"): An expression that is an rvalue may appear on the right- but not left-hand side of an assignment.

右值（发音为 are-value）：右值只能出现在赋值的右边，不能出现在赋值语句的左边。

Variables are lvalues and so may appear on the left-hand side of an assignment. Numeric literals are rvalues and so may not be assigned. Given the variables:

变量是左值，因此可以出现在赋值语句的左边。数字字面值是右值，因此不能被赋值。给定以下变量：

int units_sold = 0;
double sales_price = 0, total_revenue = 0;



it is a compile-time error to write either of the following:

下列两条语句都会产生编译错误：

// error: arithmetic expression is not an lvalue
units_sold * sales_price = total_revenue;
// error: literal constant is not an lvalue
0 = 1;



Some operators, such as assignment, require that one of their operands be an lvalue. As a result, lvalues can be used in more contexts than can rvalues. The context in which an lvalue appears determines how it is used. For example, in the expression

有些操作符，比如赋值，要求其中的一个操作数必须是左值。结果，可以使用左值的上下文比右值更广。左值出现的上下文决定了左值是如何使用的。例如，表达式

units_sold = units_sold + 1;

the variable units_sold is used as the operand to two different operators. The + operator cares only about the values of its operands. The value of a variable is the value currently stored in the memory associated with that variable. The effect of the addition is to fetch that value and add one to it.

中，units_sold 变量被用作两种不同操作符的操作数。+ 操作符仅关心其操作数的值。变量的值是当前存储在和该变量相关联的内存中的值。加法操作符的作用是取得变量的值并加 1。

The variable units_sold is also used as the left-hand side of

可以看出，左值和右值是跟左和右挂钩的。  回复  更多评论
  

++(a++)
a++ return a const object we can say it is b. so ++b is wrong  回复  更多评论
  

@whtank
高度啊 顶  回复  更多评论
  

l， r 的原始含义真的这样啊？刚才同事跟我说我还不信呢。。。  回复  更多评论
  

msdn上的，左值这种翻译并无差错。

An l-value represents a storage region's "locator" value, or a "left" value, implying that it can appear on the left of the equal sign (=). L-values are often identifiers.  回复  更多评论
  

我认为左值右值才是正确的  回复  更多评论
  

感谢楼主。。l-value r-value 真神秘  回复  更多评论
  

Expressions that refer to memory locations are called "l-value" expressions. An l-value represents a storage region's "locator" value, or a "left" value, implying that it can appear on the left of the equal sign (=). L-values are often identifiers.

The term "r-value" is sometimes used to describe the value of an expression and to distinguish it from an l-value. All l-values are r-values but not all r-values are l-values.

  回复  更多评论
  

应该是先有了l-value这个概念，r-value只是起到与lvalue对比的作用。l-value含有左的意思，但不仅仅是左的意思，r-value只有右的意思  回复  更多评论
  

@wu
不对吧，我记得赋值作为副产品的返回是R值，不是地址，你的第一个表达式就不对啊  回复  更多评论
  

感谢楼主的分享。

关于左值和右值，Dan Saks发表过一篇题为Lvalues and Rvalues的文章，阅读之感觉写的很好，概念一下清晰很多，顺便翻译了一下。有兴趣的朋友可以交流学习一下。
译文：http://filemarkets.com/file/kevinkitty/0575b639/
原文：http://www.eetimes.com/discussion/programming-pointers/4023341/Lvalues-and-Rvalues  回复  更多评论
  

@KevinKitty

不好意思，译文链接给错了，应该是：http://filemarkets.com/file/kevinkitty/03c933d9/  回复  更多评论
  

@Nash
a++相当于
int a;
{
int temp=a;
a++;
teturn temp;
}

用a++，解释a++.呵呵，太有才了
写成a=a+1.更好理解吧  回复  更多评论
  

谢谢讨论 这样百家争鸣 挺好@jie
  回复  更多评论
  

看了楼上给的原文，感觉判断lvalue和rvalue的方法就是看if it is refer to an object。因为原文中有这样一句An object is a manipulatable region of storage; an lvalue is an expression referring to an object....  回复  更多评论
  

其实我感觉左值和右值的概念吧，可能跟汇编有关。

比如 MOV A, #300

其中A就必须是物理地址，或者累加器  回复  更多评论
  

locator  回复  更多评论
  

@wu
因为自增和自减运算符是有副作用的  回复  更多评论