This function always a returns a value, although it could be the value unknown.
该函数始终返回一个值，但是该值可能是unknown。
LOCKTYPE_NOTAPPLICABLE: value is 0; this is an unknown lock type.
locktype_notapplicable：值为0，这是一种未知的锁定类型。
This is more likely to happen when the information is sensitive or of unknown value.
这在信息比较敏感或者具有未知的价值时更容易发生。
Is it possible to get a float value with unknown decimal point?
它是可能的和未知的小数点得到一个浮动值？
If a comparison value is null, the result is unknown.
如果比较值是空值，则结果未知。
It is important to start each data area with an initial value which is unknown.
重要的是每一个数据区开始初步价值不详。
It is important to start each data area with an initial value which is unknown.
重要的是每一个数据区开始初步价值不详。
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