random | 易学教程

How can I create a unique random string in laravel 5 [duplicate]

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问题 This question already has answers here : PHP: How to generate a random, unique, alphanumeric string? (27 answers) Closed 4 years ago . I am new to laravel 5. I am working on a project where I want to assign some random-readable unique string to each application. I have knowledge of the each application id which may be use as a seed. Since the app is going to be use within the company I don't worry much about security. I expect the table size to grow so my goal is to achieve uniqueness as much

undefined reference to `log'

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问题 I am trying to compile the implementation of the RFC 3797 random selection algorithm by Donald Eastlake (code: http://kambing.ui.ac.id/minix/other/rfc3797/). However, I am getting a linker error: rfc3797.c:(.text+0xe7f): undefined reference to `log' I am trying to make it with the provided Makefile, which explicitly links against the math libraray, but I still get the error: cc -lm -o randomselection rfc3797.c MD5.c How can I compile this program? 回答1: I don't know what the reason is, but if

undefined reference to `log'

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Accessing random rows from database without repetition

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问题 I have designed a quiz scenario using MySQL database as my backend. I have a total of 20 questions and I would want to display them in random order from the database. I have tried : SELECT * from mst_que ORDER BY RAND(); What the above query does is repeat few rows. 回答1: If the table contains duplicate records, use SELECT DISTINCT to filter them out. SELECT DISTINCT * FROM mst_que ORDER BY RAND() 回答2: The order by clausule needs column names or relative positions , not values or values. So .

Math类、Random类

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Math类 Math类包含执行基本数字运算的方法，如基本指数，对数，平方根和三角函数 Math类的方法全是静态方法，直接使用类名调用。 Math类中有两个常量：E和PI public static final double E：自然对数的基数。 public static final double PI：圆周长与其直径的比率，即圆周率。方法 Math类中有很多数学运算的方法，每种方法也有其对应的重载方法，以下只是部分举例，可以通过查帮助文档的方式使用更多方法。 public static double ceil(double a) 返回大于或等于参数的最小（最接近负无穷大） double值，等于一个数学整数。 public static double floor(double a) 返回小于或等于参数的最大（最接近正无穷大） double值，等于一个数学整数。 public static int max(int a,int b) 返回两个 int值中的较大值。 public static double pow(double a,double b) 将第一个参数的值返回到第二个参数的幂，即返回a的b次幂 public static int round(float a) 返回参数最接近的int ，其中int四舍五入为正无穷大。 public static double sqrt

How to generate unique random string in a length range using Golang?

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问题 I want to generate unique random string in a length range. For example, I set length is 10. and every time the generated string is unique . 回答1: How unique is unique? if Universally unique, see: https://en.wikipedia.org/wiki/Universally_unique_identifier Out of a total of 128 bits, Type 4 UUIDs have 6 reserved bits (4 for the version and 2 other reserved bits), so randomly generated UUIDs have 122 random bits. for UUID see: Is there a method to generate a UUID with go language How to display

How to generate an un-biased random number within an arbitrary range using the fewest bits

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问题 Because of the pigeon hole principle, you can't just use output = min + (rand() % (int)(max - min + 1)) to generate an unbiased, uniform, result. This answer to a similar question provides one solution but it is highly wasteful in terms of random bits consumed. For example, if the random range of the source is low, then the chances of having to generate a second value from the source can be quite high. Alternative, using a larger source range is inherently wasteful too. While I'm sure an

tp5 修改器

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修改器的使用必须使用在控制器中使用模型的方法: 控制器: public function save ( ) { $User = new UserModel ( ) ; $result = $User - > isUpdate ( false ) - > save ( [ 'username' = > '范姐' , 'num' = > 26 , 'status' = > random_int ( - 1 , 2 ) ] ) ; echo $result ; } 模型: public function setUsernameAttr ( $value ) { return $value . '1' ; } 来源： CSDN 作者： fylive 链接： https://blog.csdn.net/qq_39472229/article/details/104045360

C/C++ algorithm to produce same pseudo-random number sequences from same seed on different platforms? [duplicate]

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问题 This question already has answers here : Consistent pseudo-random numbers across platforms (6 answers) Closed 6 years ago . The title says it all, I am looking for something preferably stand-alone because I don't want to add more libraries. Performance should be good since I need it in a tight high-performance loop. I guess that will come at a cost of the degree of randomness. 回答1: Any particular pseudo-random number generation algorithm will behave like this. The problem with rand is that it

Is rand() time-dependent in php?

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问题 Let we explain what I mean. Some time ago, while writing a program in c#, I've made following mistake: int Randomize() { Random r=new Random(); return r.Next(0,10); } in c#, this is a mistake, because, called several times in a row, this function will return the same value. This is because Random constructor uses time seed, and the time difference between calls was too low (took me an hour to find that one :) ). Now I'm using rand(...) in php, and I need for the output to always be different,