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    <p>关于ipairs()和pairs(),Lua官方手册是这样说明的:</p>

pairs (t)

If t has a metamethod __pairs, calls it with t as argument and returns the first three results from the call.

Otherwise, returns three values: the next function, the table t, and nil, so that the construction

` for k,v in pairs(t) do body end`

will iterate over all key–value pairs of table t.

See function next for the caveats of modifying the table during its traversal.

ipairs (t)

If t has a metamethod __ipairs, calls it with t as argument and returns the first three results from the call.

Otherwise, returns three values: an iterator function, the table t, and 0, so that the construction

` for i,v in ipairs(t) do body end`

will iterate over the pairs (1,t[1]), (2,t[2]), …, up to the first integer key absent from the table.

根据官方手册的描述,pairs会遍历表中所有的key-value值,而pairs会根据key的数值从1开始加1递增遍历对应的table[i]值,直到出现第一个不是按1递增的数值时候退出。

. . .

下面我们以例子说明一下吧

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stars = {[1] = "Sun", [2] = "Moon", [5] = 'Earth'}
for i, v in pairs(stars) do
print(i, v)
end

使用pairs()将会遍历表中所有的数据,输出结果是:

1    Sun
2    Moon
5    Earth

如果使用ipairs()的话,

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for i, v in ipairs(stars) do

print(i, v)

end

当i的值遍历到第三个元素时,i的值为5,此时i并不是上一个次i值(2)的+1递增,所以遍历结束,结果则会是:

1    Sun
2    Moon

ipairs()和pairs()的区别就是这么简单。

还有一个要注意的是pairs()的一个问题,用pairs()遍历是[key]-[value]形式的表是随机的,跟key的哈希值有关系。看以下这个例子:

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stars = {[1] = "Sun", [2] = "Moon", [3] = "Earth", [4] = "Mars", [5] = "Venus"}

for i, v in pairs(stars) do

print(i, v)

end

结果是:

2    Moon
3    Earth
1    Sun
4    Mars
5    Venus

并没有按照其在表中的顺序输出。

但是如果是这样定义表stars的话

stars = {"Sun", "Moon", “Earth”, "Mars", "Venus"}

结果则会是

1    Sun
2    Moon
3    Earth
4    Mars
5    Venus

你清楚了吗?:)