Distinguish between an lvalue and an rvalue; show examples of each.
区分左值和右值，并举例说明。
C + + 11 standard ref for not initializing rvalue reference with lvalue?
11标准c++裁判没有初始化和左值右值引用吗？
An expression cannot be a reference, although you can bind the result of an expression with an lvalue or rvalue reference.
一个表达不能参考，虽然你可以绑定用一个表达式的结果左值或右值参考。
A value that can be used as the right-hand, but not left-hand side of an assignment. An rvalue may be read but not written.
可用于赋值操作的右边但不能用于左边的值。右值只能读而不能写。
What may be less obvisous is that we also cannot call such a function with an rvalue ( Section 2.3.1, p. 45) or with an object of a type that requires a conversion.
但比较容易忽略的是，调用这样的函数时，传递一个右值（第2.3.1 节）或具有需要转换的类型的对象同样是不允许的。
Compared with SPAD readings, the normalized redness intensity (NRI), with a high rvalue of 0.541-0.780 with conventional N parameters, could better express the N status of rice.
红光标准化值与叶绿素仪SPAD读数相比能更好地表征水稻幼穗期的氮素营养状况， 与常规测试指标的相关系数介于0.541～0.780之间。
Compared with SPAD readings, the normalized redness intensity (NRI), with a high rvalue of 0.541-0.780 with conventional N parameters, could better express the N status of rice.
红光标准化值与叶绿素仪SPAD读数相比能更好地表征水稻幼穗期的氮素营养状况， 与常规测试指标的相关系数介于0.541～0.780之间。
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