L-Value and R-Value Expressions
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.
涉及到在内存中的地址的表达式称为左值表达式。一个左值表达式代表一块存储区域的“定位”值，或者叫做一个“左”值，意味着它可以出现在等号(=)的左边，左值一般是一些标志符。
Expressions referring to modifiable locations are called “modifiable l-values.” A modifiable l-value cannot have an array type, an incomplete type, or a type with the const attribute. For structures and unions to be modifiable l-values, they must not have any members with the const attribute. The name of the identifier denotes a storage location, while the value of the variable is the value stored at that location.
一些表达式对应的是一些(在内存中)可变的地址被称为“可变左值”一个可变左值不能含有数组类型，或者是一个不完整的类型，或者是任何具有const属性的成员。标志符的名字意味着存储地址，而这个变量的值则存储在这个地址上。
An identifier is a modifiable l-value if it refers to a memory location and if its type is arithmetic, structure, union, or pointer. For example, if ptr is a pointer to a storage region, then *ptr is a modifiable l-value that designates the storage region to which ptr points.
不管一个标志符是一个算术类型，结构体，联合还是一个指针，只要它涉及到内存分配，它就是一个可变的左值。例如：如果ptr是一个指向一块内存区域的指针，那么*ptr就是一个可变左值，这个左值指出了ptr指向的区域。
Any of the following C expressions can be l-value expressions:
任何C的表达式都可以是左值表达式
An identifier of integral, floating, pointer, structure, or union type
代表整型，浮点型，指针型，结构体或者一个联合类型
A subscript ([ ]) expression that does not evaluate to an array
不代表数组的下标运算符
A member-selection expression (–> or .)
成员选择符(–> or .)
A unary-indirection (*) expression that does not refer to an array
不代表数组的指针运算符
An l-value expression in parentheses
在圆括号中的左值运算符
A const object (a nonmodifiable l-value)
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.
一个常量对象(一个不变的左值)，“右值”这个术语常常被用来描述表达式的值和用来区别与左值，所有的左值都是右值，但反之并不成立
Microsoft Specific —>
Microsoft C includes an extension to the ANSI C standard that allows casts of l-values to be used as l-values, as long as the size of the object is not lengthened through the cast. (See Type-Cast Conversions for more information.) The following example illustrates this feature:
Microsoft C对标准C进行了扩展，它允许左值到左值的转化，只要这个对象的长度不超出这个转换(更多的请参见类型转化)下例说明这个特性。
char *p ;
short i;
long l;
(long *) p = &l ; /* Legal cast */
(long) i = l ; /* Illegal cast */
The default for Microsoft C is that the Microsoft extensions are enabled. Use the /Za compiler option to disable these extensions.
Microsoft C默认该扩展，可以在编译时使用/Za选项关闭它
END Microsoft Specific
