那么對于（a=2）=66這樣的表達式怎么看?另外，為什么自增（減）運算只能用于左值，不能用于右值，即表達式++（a++）為什么錯誤呢？  回復  更多評論
  

@wu
（a=2）=66 中就是按順序賦值就是了 所以a=66

++（a++）
至于右值為什么不能用，因為后增量(后減量)返回的值是修改前的變量值，故不為左值，所以他就不能用了  回復  更多評論
  

++（a++）
a++相當于
int a;
{
int temp=a;
a++;
teturn temp;
}
所以我們可以將++(a++)看成++temp;而temp
顯然是一個右值，所以不能用啊~~  回復  更多評論
  

錯了，沒有什么左值和右值！
翻譯害人不淺，
L-value中的L指的是Location，表示可尋址。The "l" in lvalue can be though of as location
R-value中的R指的是Read，表示可讀。The "r" in rvalue can be thought of as "read" value.  回復  更多評論
  

原創(chuàng)好文章，謝謝樓主。  回復  更多評論
  

From Wikipedia, the free encyclopedia
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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

翻譯不對,謝謝  回復  更多評論
  

這是<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++:

我們在第五章再詳細探討表達式，現(xiàn)在先介紹 C++ 的兩種表達式：

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（發(fā)音為 ell-value）：左值可以出現(xiàn)在賦值語句的左邊或右邊。

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（發(fā)音為 are-value）：右值只能出現(xiàn)在賦值的右邊，不能出現(xiàn)在賦值語句的左邊。

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:

變量是左值，因此可以出現(xiàn)在賦值語句的左邊。數(shù)字字面值是右值，因此不能被賦值。給定以下變量：

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



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

下列兩條語句都會產(chǎn)生編譯錯誤：

// 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，比如賦值，要求其中的一個操作數(shù)必須是左值。結(jié)果，可以使用左值的上下文比右值更廣。左值出現(xiàn)的上下文決定了左值是如何使用的。例如，表達式

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 變量被用作兩種不同操作符的操作數(shù)。+ 操作符僅關心其操作數(shù)的值。變量的值是當前存儲在和該變量相關聯(lián)的內(nèi)存中的值。加法操作符的作用是取得變量的值并加 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掛鉤的。  回復  更多評論
  

++(a++)
a++ return a const object we can say it is b. so ++b is wrong  回復  更多評論
  

@whtank
高度啊 頂  回復  更多評論
  

l， r 的原始含義真的這樣啊？剛才同事跟我說我還不信呢。。。  回復  更多評論
  

msdn上的，左值這種翻譯并無差錯。

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.  回復  更多評論
  

我認為左值右值才是正確的  回復  更多評論
  

感謝樓主。。l-value r-value 真神秘  回復  更多評論
  

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.

  回復  更多評論
  

應該是先有了l-value這個概念，r-value只是起到與lvalue對比的作用。l-value含有左的意思，但不僅僅是左的意思，r-value只有右的意思  回復  更多評論
  

@wu
不對吧，我記得賦值作為副產(chǎn)品的返回是R值，不是地址，你的第一個表達式就不對啊  回復  更多評論
  

感謝樓主的分享。

關于左值和右值，Dan Saks發(fā)表過一篇題為Lvalues and Rvalues的文章，閱讀之感覺寫的很好，概念一下清晰很多，順便翻譯了一下。有興趣的朋友可以交流學習一下。
譯文：http://filemarkets.com/file/kevinkitty/0575b639/
原文：http://www.eetimes.com/discussion/programming-pointers/4023341/Lvalues-and-Rvalues  回復  更多評論
  

@KevinKitty

不好意思，譯文鏈接給錯了，應該是：http://filemarkets.com/file/kevinkitty/03c933d9/  回復  更多評論
  

@Nash
a++相當于
int a;
{
int temp=a;
a++;
teturn temp;
}

用a++，解釋a++.呵呵，太有才了
寫成a=a+1.更好理解吧  回復  更多評論
  

謝謝討論 這樣百家爭鳴 挺好@jie
  回復  更多評論
  

看了樓上給的原文，感覺判斷l(xiāng)value和rvalue的方法就是看if it is refer to an object。因為原文中有這樣一句An object is a manipulatable region of storage; an lvalue is an expression referring to an object....  回復  更多評論
  

其實我感覺左值和右值的概念吧，可能跟匯編有關。

比如 MOV A, #300

其中A就必須是物理地址，或者累加器  回復  更多評論
  

locator  回復  更多評論
  

@wu
因為自增和自減運算符是有副作用的  回復  更多評論