ios 使用 arc4random() 时如何选择值的范围
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How to select range of values when using arc4random()
提问by NextRev
Can I set a range of numbers when using arc4random()? For example 50-100 only.
使用 arc4random() 时可以设置数字范围吗？例如仅 50-100。
回答by RunLoop
As pointed out in other posts below, it is better to use arc4random_uniform. (When this answer was originally written, arc4random_uniformwas not available). Besides avoiding the modulo bias of arc4random() % x, it also avoids a seeding problem with arc4randomwhen used recursively in short timeframes.
正如下面其他帖子所指出的，最好使用arc4random_uniform. （最初编写此答案时，arc4random_uniform不可用）。除了避免 的模偏差外arc4random() % x，它还避免了arc4random在短时间内递归使用时的播种问题。
arc4random_uniform(4)
will generate 0, 1, 2 or 3. Thus you could use:
将生成 0、1、2 或 3。因此您可以使用：
arc4random_uniform(51)
and merely add 50 to the result to get a range between 50 & 100 (inclusive).
只需将 50 添加到结果中即可获得 50 和 100（含）之间的范围。
回答by Justyn
To expand upon JohnK comment.
扩展 JohnK 的评论。
It is suggested that you use the following function to return a ranged random number:
建议您使用以下函数返回一个范围随机数：
arc4random_uniform(51)
which will return a random number in the range 0to 50.
这将返回范围内的随机数0到50.
Then you can add your lower bounds to this like:
然后你可以添加你的下限，如：
arc4random_uniform(51) + 50
which will return a random number in the range 50to 100.
这将返回范围内的随机数50到100.
The reason we use arc4random_uniform(51)over arc4random() % 51is to avoid the modulo bias. This is highlighted in the man page as follows:
我们使用arc4random_uniform(51)over的原因arc4random() % 51是为了避免模偏差。这在手册页中突出显示如下：
arc4random_uniform(upper_bound) will return a uniformly distributed random number less than upper_bound. arc4random_uniform() is recommended over constructions like ``arc4random() % upper_bound'' as it avoids "modulo bias" when the upper bound is not a power of two.
arc4random_uniform(upper_bound) 将返回一个小于 upper_bound 的均匀分布的随机数。arc4random_uniform() 被推荐用于类似 ``arc4random() % upper_bound'' 的结构，因为当上限不是 2 的幂时，它可以避免“模偏差”。
In short you get a more evenly distributed random number generated.
简而言之，您会得到一个更均匀分布的随机数。
回答by Vaibhav Saran
int fromNumber = 10;
int toNumber = 30;
int randomNumber = (arc4random()%(toNumber-fromNumber))+fromNumber;
Will generate randon numberbetween 10and 30, i.e. 11,12,13,14......29
将randon number在10和之间生成30，即11,12,13,14......29
回答by handiansom
You can use this code for generating random values with range:
您可以使用此代码生成具有范围的随机值：
//range from 50 to 100
int num1 = (arc4random() % 50) + 50; or
int num1 = arc4random_uniform(50) + 50;
//range from 0-100
int num1 = arc4random() % 100; or
int num1 = arc4random_uniform(100);
回答by kurtanamo
In Swift you can use this (inspired by answer of @Justyn)
在 Swift 中，您可以使用它（灵感来自@Justyn的回答）
func generateRandomKey(fromRange rangeFrom:Int, toRange rangeTo:Int) -> Int{
let theKey = arc4random_uniform(UInt32(rangeTo - rangeFrom)) + UInt32(rangeFrom)
return Int(theKey)
}
Will always give you a random range Integer.
总是会给你一个随机范围的整数。
回答by Mike Young
In many situations 10 thru 30 would mean inclusive, (includes 10 and 30) ...
在许多情况下，10 到 30 表示包含，（包括 10 和 30）......
int fromNumber = 10;
int toNumber = 30;
toNumber ++;
int randomNumber = (arc4random()%(toNumber-fromNumber))+fromNumber;
Notice the difference toNumber - fromNumber is now 21 ... (20+1) which yields the possible results of 0 thru 20 (inclusive) which when added to fromNumber (10) results in 10 thru 30 (inclusive).
请注意 toNumber - fromNumber 现在的不同之处是 21 ... (20+1) 这会产生 0 到 20（含）的可能结果，当添加到 fromNumber (10) 时会产生 10 到 30（含）。
