blocks|key|4191924|text|不要在每次想要生成数字时都调用srand。srand初始化伪随机数生成器，并且只在程序开始时或您想要重置生成器时调用一次。通过每次重置它，您可以强制rand在时钟上的每一秒内调用它时生成相同的数字。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4191925|请勿使用x+%25+n将数字减少到所需的范围。rand的旧实现是出了名的糟糕，并且在低位有模式。相反，请使用x+/+((RAND_MAX%2B1u)+/+n)。|4191926|代码int+range+=+RAND_MAX+-+(RAND_MAX+%25+n);有缺陷。假设n为4，RAND_MAX为7，意味着rand返回0到7。这段代码将range设置为4，然后while+(x+>+range)+x+=+rand();丢弃5、6和7，同时保留4。这里有两个错误:代码保留0、1、2、3和4这五个值，这与所需的4范围不匹配(不是4的倍数)，并且不必要地丢弃这些值。如果我们保留了4，5，6和7，我们就会有一个匹配。您可以使用：|4191927|unsigned+range+=+(RAND_MAX+%2B+1u)+-+((RAND_MAX+%2B+1u)+%25+n);|code-block|syntax|javascript|4191928|和：|4191929|while+(x+>=+range)+x+=+rand();|4191930|如果您正在使用C%2B%2B，请切换到使用std::uniform_int_distribution。如果您使用的是C，请检查您的实现中的rand质量，或者切换到另一个生成器，例如POSIX+srandom和random。|4191931|entityMap|0|LINK|mutability|MUTABLE|url|http://en.cppreference.com/w/cpp/numeric/random/uniform_int_distribution^0|F|5|L|5|22|4|0|4|5|L|4|1G|N|0|2|12|1A|1|1E|8|1S|4|27|5|2J|T|0|0|0|0|H|T|1T|4|2K|7|2S|6|H|T|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|19|8|@$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1G|8|@$9|1H|A|1I|B|C]|$9|1J|A|1K|B|C]|$9|1L|A|1M|B|C]|$9|1N|A|1O|B|C]|$9|1P|A|1Q|B|C]|$9|1R|A|1S|B|C]]|D|@]|E|$]]|$1|J|3|K|5|L|7|1T|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1U|8|@]|D|@]|E|$]]|$1|Q|3|R|5|L|7|1V|8|@]|D|@]|E|$M|N]]|$1|S|3|T|5|6|7|1W|8|@$9|1X|A|1Y|B|C]|$9|1Z|A|20|B|C]|$9|21|A|22|B|C]|$9|23|A|24|B|C]]|D|@$9|25|A|26|1|27]]|E|$]]|$1|U|3|-4|5|6|7|28|8|@]|D|@]|E|$]]]|V|$W|$5|X|Y|Z|E|$10|11]]]]

Do not call <code>srand</code> every time you want to generate a number. <code>srand</code> initializes the pseudo-random number generator and is intended to be called just once at the start of your program, or when you want to reset the generator. By resetting it every time, you are forcing <code>rand</code> to generate the same numbers every time you call it within each second on the clock.

Do not use <code>x % n</code> to reduce the number to a desired range. Old implementations of <code>rand</code> are notoriously bad and have patterns in the low bits. Instead, use <code>x / ((RAND_MAX+1u) / n)</code>.

The code <code>int range = RAND_MAX - (RAND_MAX % n);</code> is flawed. Suppose <code>n</code> is 4 and <code>RAND_MAX</code> is 7, meaning <code>rand</code> returns 0 to 7. This code sets <code>range</code> to 4, and then <code>while (x &gt; range) x = rand();</code> discards 5, 6, and 7, while it retains 4. There are two bugs here: The code keeps the five values 0, 1, 2, 3, and 4, which is a mismatch to (not a multiple of) the desired range of 4, and it unnecessarily discards values. If we had kept 4, 5, 6, and 7, we would have a match. You could use:

<pre><code>unsigned range = (RAND_MAX + 1u) - ((RAND_MAX + 1u) % n);
</code></pre>

and:

<pre><code>while (x &gt;= range) x = rand();
</code></pre>

If you are using C++, switch to using <a href="http://en.cppreference.com/w/cpp/numeric/random/uniform_int_distribution" rel="nofollow noreferrer"><code>std::uniform_int_distribution</code></a>. If you are using C, check the quality of <code>rand</code> in your implementation or switch to another generator such as the POSIX <code>srandom</code> and <code>random</code>.

blocks|key|4191963|text|正如其他地方所指出的，修复重复数字的方法是将对srand(time(NULL))的调用移到此函数之外，并且在开始时每个程序只调用一次。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4191964|至于为什么会得到重复的数字:该函数每秒被调用几次。每次函数在给定的时间内执行时，time(NULL)都会返回相同的数字，此代码使用该数字来为随机数生成器提供种子。|4191965|从特定种子生成的随机数序列始终是相同的。此代码从该序列中获取第一个数字，该数字在一秒钟内始终相同，直到time(NULL)返回一个新值。|4191966|entityMap^0|N|H|0|14|A|0|1F|A|0^^$0|@$1|2|3|4|5|6|7|L|8|@$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|R|8|@$9|S|A|T|B|C]]|D|@]|E|$]]|$1|J|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|K|$]]

As noted elsewhere, the fix to the repeated numbers is to move the call to <code>srand(time(NULL))</code> outside this function and call it only once per program at the beginning.

As for why you're getting repeated numbers: The function is being called several times per second. Each time the function executes in a given second, <code>time(NULL)</code> returns the same number, which this code uses to seed the random number generator. 

The sequence of random numbers generated from a particular seed will always be the same. This code takes the first number from that sequence, which is always the same for one second, until <code>time(NULL)</code> returns a new value.

I'm trying to generate 10,000 random numbers in a row in C and am having trouble getting random or even randomish results using the pseudo RNG. I used modulus in a way that I think should create uniformity, which it does, but the results are equivalent to 0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,3,3,3,3,3,3,3 etc. when run in a loop in another function calling RNG(4).

<pre><code>int RNG(int n) {
 int range = RAND_MAX - (RAND_MAX % n);
 srand(time(NULL));
 int x = rand();
 while (x &gt; range) {
 x = rand();
 }
 return x % n;
}
</code></pre>

Any way to get it closer to 1,3,2,0,2,3,1,0,0,3,2,0,1 etc. would be appreciated!

Thank you!

EDIT: Thanks for the responses everyone! Moved the seeding to the start of the function calling RNG and everything is dandy now!

Repeated and Predictable RNG Values in C

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

我试图在C中连续生成10,000个随机数，但使用伪RNG无法获得随机甚至随机的结果。我以一种我认为应该创建一致性的方式使用了模数，它确实如此，但当在另一个调用RNG(4)的函数中循环运行时，结果等同于0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,3,3,3,3,...

问C语言中重复且可预测的RNG值
EN

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问C语言中重复且可预测的RNG值EN

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问C语言中重复且可预测的RNG值
EN