How to define constants in php: 1. Use the define() function to define, the syntax "define (constant name, constant value, whether case sensitive)"; 2. Use the const keyword to define, the syntax "const Constant name = constant value;".
The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer
How to define constants in php
define() function
const keyword
Compared with variables, Constants have the following characteristics:
There is no dollar sign ($) in front of the constant;
Constant can only be defined with define() and const ;
The scope of constants is global;
Once a constant is defined, it cannot be redefined or undefined.
define() function defines constants
Legal constant names can only start with letters and underscores, and can be followed by letters of any length, Numbers or underscores. In PHP, you can define a constant through the define() function. The syntax of the define() function is as follows:
define($name, $value , $case_insensitive)
$name Required parameters, constant name (need to use double quotes Or wrapped in single quotes)
$value Required parameter, the value of the constant
$case_insensitive Optional parameter, specifies whether it is case sensitive, The default is case-sensitive. If set to true, it means that it is not case-sensitive
<?php header("Content-type:text/html;charset=utf-8"); define('WebSite', 'php中文网'); echo WebSite.'<br>'; ?>
const keyword definition constant
Syntax:
const 常量名 = 常量值;
Example:
<?php const FOO = 'BAR'; echo FOO.'<br>'; ?>
##The difference between define() and const:
const defines constants at compile time, while the define() method defines constants at runtime. const cannot be used in if statements, defne() can be used in if statements.if(...) { const FOO = 'BAR';//错误 } if(...) { define('FOO', 'BAR');//正确 }define() A common scenario is to first determine whether the constant has been defined before defining the constant:
if(defined('FOO)) { define('FOO', 'BAR') }const When defining a constant, the value can only be a static scalar (number, string, true , false, null), and the define() method can use the value of any expression as the value of a constant. Starting from PHP 5.6, const also allows expressions to be used as the value of constants.
const BIT_5 = 1 << 5; //PHP5.6后支持,之前的PHP版本不支持 define('BIT_5', 1 << 5);// 所有PHP版本都支持const 只允许简单的常量名,而define()可以把任何表达式的值用作常量名
for ($i = 0; $i < 32; $i++) { define('BIT_' . $i, 1 << $i); }const The constant names defined are case-sensitive, and case-insensitive constants can be defined by passing true to the third parameter of the define() method.
define('FOO', 'BAR', true); echo FOO; //BAR echo foo; //BARListed above are some shortcomings or inflexibility of const compared to define(). Let’s take a look at why I personally recommend using const instead of define() to define constants (unless you need to Define constants in the scenarios listed above). const has better readability, const is a language structure rather than a function, and is consistent with the form of defining class constants in a class. const defines constants in the current namespace, and define() must pass the complete namespace name when defining to achieve similar effects:
namespace A\B\C; //To define the constant A\B\C\FOO: const FOO = 'BAR'; define('A\B\C\FOO', 'BAR');Recommended learning: "
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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。

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。

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。

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。

查找方法:1、用strpos(),语法“strpos("字符串值","查找子串")+1”;2、用stripos(),语法“strpos("字符串值","查找子串")+1”。因为字符串是从0开始计数的,因此两个函数获取的位置需要进行加1处理。


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