


A brief analysis of the implementation of PHP regular expression matching
PHP regular expression matching is the ultimate goal when we talk about the application of regular expressions in PHP, so how to implement PHP regular expression matching Woolen cloth? What specific method will be used? Let’s take a look at the specifics.
PHP inherits the tradition of UNIX and fully supports the processing of regular expressions. Regular expressions provide an advanced, but non-intuitive, method of string matching and processing. Friends who have used PERL's regular expressions know that regular expressions are very powerful, but they are not easy to learn.
PHP regular expression matching example application:
<ol class="dp-c"><li class="alt"><span><span>^.+@.+..+$ </span></span></li></ol>
This effective but incomprehensible code is enough to give some programmers a headache (me) or make them Give up using regular expressions. I believe that after you finish reading this tutorial, you will understand the meaning of this code.
Basic pattern matching of PHP regular expression matching
Everything starts from the most basic. Patterns are the most basic elements of regular expressions. They are a set of characters that describe the characteristics of a string. Patterns can be simple, consisting of ordinary strings, or very complex, often using special characters to represent a range of characters, recurrences, or to represent context. For example:
^once
This pattern contains a special character ^, which means that the pattern only matches those strings starting with once. For example, this pattern matches the string "once upon a time" but does not match "There once was a man from NewYork". Just like the ^ symbol indicates the beginning, the $ symbol matches strings that end with a given pattern.
bucket$
This pattern matches "Who kept all of this cash in a bucket" but does not match "buckets". When the characters ^ and $ are used together, they represent an exact match (strings are the same as patterns). For example:
^bucket$
only matches the string "bucket". If a pattern does not include ^ and $, then it matches any string that contains the pattern. For example: the pattern
once
matches the string
<ol class="dp-c"> <li class="alt"><span><span>There once was a man from NewYork </span></span></li> <li><span>Who kept all of his cash in a bucket. </span></li> </ol>
.
The letters (o-n-c-e) in this pattern are literal characters, that is, they represent the letters themselves, and the same goes for numbers. Other slightly more complex characters, such as punctuation and white characters (spaces, tabs, etc.), require escape sequences. All escape sequences begin with a backslash (). The escape sequence for the tab character is: t. So if we want to detect whether a string starts with a tab character, we can use this pattern:
^t
Similarly, use n to represent "new line" , r means carriage return. Other special symbols can be used with a backslash in front, such as the backslash itself is represented by ., the period is represented by ., and so on.
This concludes the introduction to PHP regular expression matching. I hope it will be helpful for you to understand and learn PHP regular expression matching.

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。

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。

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。

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。

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。

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。


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