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仔細(xì)查閱了一些資料，發(fā)現(xiàn)對(duì)于lvalue和rvlaue的說(shuō)明各有不同。找了兩個(gè)比較經(jīng)典的說(shuō)法，共同參考一下。下面是在comp.lang.c++.moderated上找到的（為避免斷章取義，貼全文）：
The simplest explanation I know is that an rvalue, in current C++, is an *expression* that produces a value, e.g. 42, and an lvalue is an *expression* that just refers to some existing object or function[1]. Hence the acronym "locator value"[2], which however is still misleading because an lvalue is simply not a value. Better would be *rexpression* versus *lexpression*, and even better, just value versus reference (unfortunately the term "reference" is already hijacked).
"object" versus "value": in C++ the basic definition of "object" is a region of storage, i.e. anything that actually occupies storage, while a pure value such as 42 doesn't necessarily occupy any storage. A value (an rvalue) can be an object, though. If it is, then it's a temporary object.
C++ allows you to call member functions on a class type rvalue, i.e. on a temporary class type object.
The ability to call member functions on (class type) rvalues, together with C++'s treatment of assignment operator as a member function (automatically generated if needed and none defined), means that you can assign to class type rvalues. However, C++ does not regard that rvalue to be *modifiable*: to be
well-defined, the assignment must do something else than modifiying the object assigned to (and typically we indicate that by declaring the assignment operator const). §3.10/14 "A program that attempts to modify an object through a nonmodifyable lvalue or rvalue expression is ill-formed".
Fine point: §3.10/14 means that rvalue-ness transfers to parts of an rvalue, which are thereby also considered rvalues. However, at least the two compilers I use don't seem to know that rule. Comeau Online does.
I'm not sure if the explanation above holds up with respect to C++0x rvalue references. rvalue versus lvalue got a lot more complicated in C++ than in original C. Perhaps it's even more complicated in C++0x, I don't know. :-)
Cheers, & hth.,
- Alf
Notes:
[1] Amazingly that's also the general definition the standard starts out with, before going into details: §3.10/2 "An lvalue refers to an object or function", however, it would have helped much if the word "expression" was explicitly included there, not just by being mentioned in the preceding paragraph.
[2] Unfortunately the C++ standard doesn't use or even mention the acronym "locator value". This acronym comes from the current C standard. And ironically the C++ standard mentions, by contextual placement, the original old C acronym of "left hand value", in §3.10/4: "built-in assignment operators all expect their left hand operands to be lvalues".
Programming Cpp的解釋：
http://etutorials.org/Programming/Programming+Cpp/Chapter+3.+Expressions/3.1+Lvalues+and+Rvalues/你的解釋更接近真相，呵呵，不過(guò)我還是不同意地址一說(shuō)，用引用會(huì)比較好一些。要不你整理一下，就lvalue和rvalue專門寫一篇？
看來(lái)俺還得多看看標(biāo)準(zhǔn)啊。
我的C++標(biāo)準(zhǔn)丟了，給發(fā)一個(gè)？raof01@gmail.com。