Use define() function in php to define a constant. The so-called constant refers to a quantity whose value does not change. This article collects several articles about PHP constants. I hope it will be helpful to everyone's understanding of PHP constants. Let's take a look.
1.Detailed explanation of the definition and usage examples of PHP constants
We can understand constants as quantities whose values do not change. Once a constant is defined, it cannot be changed anywhere else in the program script.
How to define constants: Constants are composed of English letters, underscores, and numbers. However, one thing to note is that the first letter of our constants cannot start with a number.
In PHP we use the define() function to define constants. The syntax of the define() function is as follows
2.Detailed explanation of PHP predefined constant examples
We can use PHP's predefined constants to obtain information in PHP. For example, we can use it to obtain the operating system of the current computer, the currently used PHP version information, etc. Some predefined constants commonly used in PHP are as follows: __FILE__ Default constant, PHP program file name; __LINE__ Default constant, number of PHP program lines
3.The relationship and difference between php constants and variables
Let’s first look at the difference between the two from the definition of php constants and variables:Constant : In PHP we use the define() function to define constants. For details, see: Detailed explanation of the definition and usage examples of PHP constants. Variables: All variables in PHP start with $, followed by the name of the variable, and assign a value to the variable. From the definition of PHP constants and variables, we can get: There is no dollar sign ($) in front of the constant; Constant can only be defined with the define() function, and Cannot pass assignment statements;
4.Detailed explanation of magic constant examples in php
When explaining PHP constants, we know that PHP Most of the constants in are unchanged, but there are 8 predefined constants that will change as the location of the code where they are located changes. These 8 constants are called magic constants. These special constants are not case-sensitive. PHP's "magic constants" are in the following table
5.Detailed explanation of php class constant definitions and examples
In hp we can understand that the value does not change The quantity is called a constant. So, what is a class constant? In fact, class constants are also easy to understand. We can call the value that always remains unchanged in the class a constant, and this constant can be called a class constant. Be sure to remember that you do not need to use the "$" symbol when defining and using constants.
Class constants belong to the class itself, not to object instances, and cannot be accessed through object instances
* Cannot be modified with public, protected, private, static
* Subclasses can be repeated To write constants in the parent class, you can call the constants in the parent class through (parent::)
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php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($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。

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。

在PHP中,可以利用implode()函数的第一个参数来设置没有分隔符,该函数的第一个参数用于规定数组元素之间放置的内容,默认是空字符串,也可将第一个参数设置为空,语法为“implode(数组)”或者“implode("",数组)”。


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