Preface
The PHP uniqid() function can be used to generate a unique identifier that is not repeated, which is based on the current timestamp in microseconds. In cases of high concurrency or extremely short intervals (such as loop code), a large amount of duplicate data will appear. Even if the second parameter is used, it will be repeated, and the best solution is to combine the md5 function to generate a unique ID.
Use function
string uniqid ([ string $prefix = "" [, bool $more_entropy = false ]] )
Get a prefixed unique ID based on the number of microseconds in the current time. prefix Useful parameter. For example: if on multiple hosts a unique ID might be generated in the same microsecond. If prefix is empty, the length of the returned string is 13. If moreentropy is TRUE, the length of the returned string is 23. moreentropy If set to TRUE, uniqid() will add extra entropy to the end of the returned string (using a combined linear congruential generator). Make the unique ID more unique.
PHP uniqid() method to generate non-repeating unique identifiers
This method will generate a large amount of repeated data. Running the following PHP code will generate the unique identifier and the corresponding element value in the array index. is the number of times the unique identifier is repeated.
<?php $units = array();for($i=0;$i<1000000;$i++){ $units[] = uniqid();} $values = array_count_values($units); $duplicates = [];foreach($values as $k=>$v){ if($v>1){ $duplicates[$k]=$v; }} echo '<pre class="brush:php;toolbar:false">';print_r($duplicates); echo '';?>
PHP uniqid() Method 2 for generating non-duplicate unique identifiers
The amount of duplicate unique identifiers generated by this method is significantly reduced.
<?php $units = array();for($i=0;$i<1000000;$i++){ $units[] = uniqid('',true);} $values = array_count_values($units); $duplicates = [];foreach($values as $k=>$v){ if($v>1){ $duplicates[$k]=$v; }} echo '<pre class="brush:php;toolbar:false">';print_r($duplicates); echo '';?>
PHP uniqid() Generate non-duplicate unique identification method three
There is no duplication in the unique identification generated by this method.
<?php $units = array();for($i=0;$i<1000000;$i++){ $units[]=md5(uniqid(md5(microtime(true)),true));} $values = array_count_values($units); $duplicates = [];foreach($values as $k=>$v){ if($v>1){ $duplicates[$k]=$v; }} echo '<pre class="brush:php;toolbar:false">';print_r($duplicates); echo '';?>
PHP uniqid() generates unique identifier method four
Use the sessioncreateid() function to generate a unique identifier. After actual testing, it was found that even if sessioncreateid() is called cyclically 100 million times, the There has been no duplication. php sessioncreateid() is a new function in PHP 7.1, which is used to generate session id. It cannot be used in lower versions.
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php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。

在php中,可以使用substr()函数来读取字符串后几个字符,只需要将该函数的第二个参数设置为负值,第三个参数省略即可;语法为“substr(字符串,-n)”,表示读取从字符串结尾处向前数第n个字符开始,直到字符串结尾的全部字符。


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