问题
I'm fairly new to Lua. While testing I discovered #INF
/#IND
. However, I can't find a good reference that explains it.
What are #INF
, #IND
, and similar (such as negatives) and how do you generate and use them?
回答1:
#INF
is infinite, #IND
is NaN. Give it a test:
print(1/0)
print(0/0)
Output on my Windows machine:
1.#INF
-1.#IND
As there's no standard representation for these in ANSI C, you may get different result. For instance:
inf
-nan
回答2:
Expanding @YuHao already good answer.
Lua does little when converting a number to a string, since it heavily relies on the underlying C library implementation. In fact Lua print implementation calls Lua tostring
which in turn (after a series of other calls) uses the lua_number2str macro, which is defined in terms of C sprintf. Thus in the end you see whatever representation for infinities and NaNs the C implementation uses (this may vary according to which compiler was used to compile Lua and which C runtime your application is linked to).
回答3:
@YuHao has already pointed out what means +/-1.#INF (+-inf) and -1.#IND (nan), so I will just add how to deal with it (which I just needed to) in Lua:
- "inf" (+/- 1.#INF) are the higher number values that (Lua/C) can represent and the language provides that constant for you: "math.huge". So you can test a number inside Lua for +-INF; the function "isINF()" below shows how to use it.
- "nan" (- 1.#IND) is something that can not be handled numerically: it should be a number, its not, and anything you do with it is anything but a number also. with that in mind remember that no NaN is equal to other NaN; check for NaN like the function "isNAN()" below.
local function isINF(value)
return value == math.huge or value == -math.huge
end
local function isNAN(value)
return value ~= value
end
来源:https://stackoverflow.com/questions/19107302/in-lua-what-is-inf-and-ind