PHP学习笔记一、基础知识
一、PHP四种写法
1、XML标记风格:
<?php ...?>
2、短标记(需要在PHP配置文件中修改):...?>
3、ASP风格(需要在PHP配置文件中修改):
4、Script风格:<script language="php">...</script>
二、PHP注释
1、c++风格的单行注释:"//"。
2、shell风格的单行注释:"#"。
3、c风格的多行注释:"/* */"。
三、PHP变量
1、PHP不要求再使用之前声明变量,第一次给一个变量赋值时,你才创建了一个变量。
2、PHP中声明变量必须以"$"开始,后面跟变量名。
3、变量名以字母,数字、下划线组成,但是不能以数字开头。变量名称区分大小写。
4、变量名必须要有意义。
5、可变变量。
6、变量的作用域是局部的(方法外的变量不能在方法内使用,方法内的变量不能在方法外使用)。
7、常量的作用域是全局的(在整个脚本中都可以使用,使用define函数进行定义常量)。<code> php$a="chuangen3";$chuangen1="今天天气真好!";$chuangen2="我要出去玩!";$chuangen3="我要学PHP!";echo $$a;?></code>
6、引用赋值
<code> php$a=100;$b=&$a;//将a的地址赋给b,a和b指向同一个内存地址。$a=200; echo $b;?></code>
四、PHP数据类型
var_dump(变量名):查看变量的类型。如:
$a=100 var_dump($a); 输出:int
。
1、基本数据类型
整型(integer)、浮点型(float或double)、布尔型(boolean)、字符串(string)。
PHP没有对字符串的最大长度进行严格的规定。
可以使用单引号和双引号和界定符(一般用于多行字符)来定义字符串。
单引号和双引号的区别:双引号支持解析变量名,和解析转义符。单引号不支持。
<code><?php $a="php100";$b="$a 欢迎您!"//双引号中的变量可以被解析,单引号就不行。echo $b;//使用界定符来定义多行字符串$c=<<<EEE今天天气真好真好真真好又下雨了!!!!EEE;echo $c;?></code>
当没有上面的要求时,尽量使用单引号来定义字符串。因为单引号执行效率高。
2、复合数据类型
2.1、数组(Array)<?php $a=array("php100",100,3.33,true); var_dump($a); ?>
2.2、对象(Object)<code><?phpclass A{ public $a=100; public $b=3.33; public $c="php100"; public $d=false; public $e=array(1,2,3); public function fun(){ echo" chuang enIT教育"; }$obj=new A();var_dump($obj);}?></code>
3、特殊数据类型
3.1、NULL:表示一个变量的值为空,不区分大小写。
在下列情况下变量被认为是NULL;
(1)、将变量直接赋值为NULL。$a=null;
(2)、声明的变量尚未被赋值。var_dump($a);
(3)、被unset函数销毁的变量。$a=100 unset($a); var_dump($a);
3.2、资源类型(resource)
资源是一种特殊类型的变量,保存了到外部资源的一个引用。资源是通过专门的函数来建立和使用的。
<code><?php $a=fopen("./demo.php","r");var_dump($a);?></code>
五、数据类型转换
字符串转换成整型。从左往右数第一个非数字后的内容全部舍掉。
$a='100php100'; $b=(int)$a; var_dump($b); 输出:int 100
自动转换
<code><?php $a='100.33php100';$b=200;$c=$a+$b;var_dump($c);//输出:float 300.33?></code>
六、常量
1、常量的作用域是全局的,在脚本的任何地方都可以声明和访问。
2、常量只包含布尔型、整型、浮点型和字符串类型。
3、按照惯例,常量标识符总是答谢的;常量前没有“$”符号。自定义常量
<code><?phpdefine ("ABC",100);//默认区分大小写echo ABC; define("ABC",100,true);//不区分大小写echo abc;//输出:100?></code>
系统常量
<code><?phpecho __FILE__;//当前文件所在路径echo "<br />";//换行echo __LINE__;//当前语句所在行号echo "<br>";echo PHP_VERSION;//php版本号echo "<br>";echo PHP_OS;//当前windows操作系统?></code>

PHPsessionstrackuserdataacrossmultiplepagerequestsusingauniqueIDstoredinacookie.Here'showtomanagethemeffectively:1)Startasessionwithsession_start()andstoredatain$_SESSION.2)RegeneratethesessionIDafterloginwithsession_regenerate_id(true)topreventsessi

In PHP, iterating through session data can be achieved through the following steps: 1. Start the session using session_start(). 2. Iterate through foreach loop through all key-value pairs in the $_SESSION array. 3. When processing complex data structures, use is_array() or is_object() functions and use print_r() to output detailed information. 4. When optimizing traversal, paging can be used to avoid processing large amounts of data at one time. This will help you manage and use PHP session data more efficiently in your actual project.

The session realizes user authentication through the server-side state management mechanism. 1) Session creation and generation of unique IDs, 2) IDs are passed through cookies, 3) Server stores and accesses session data through IDs, 4) User authentication and status management are realized, improving application security and user experience.

Tostoreauser'snameinaPHPsession,startthesessionwithsession_start(),thenassignthenameto$_SESSION['username'].1)Usesession_start()toinitializethesession.2)Assigntheuser'snameto$_SESSION['username'].Thisallowsyoutoaccessthenameacrossmultiplepages,enhanc

Reasons for PHPSession failure include configuration errors, cookie issues, and session expiration. 1. Configuration error: Check and set the correct session.save_path. 2.Cookie problem: Make sure the cookie is set correctly. 3.Session expires: Adjust session.gc_maxlifetime value to extend session time.

Methods to debug session problems in PHP include: 1. Check whether the session is started correctly; 2. Verify the delivery of the session ID; 3. Check the storage and reading of session data; 4. Check the server configuration. By outputting session ID and data, viewing session file content, etc., you can effectively diagnose and solve session-related problems.

Multiple calls to session_start() will result in warning messages and possible data overwrites. 1) PHP will issue a warning, prompting that the session has been started. 2) It may cause unexpected overwriting of session data. 3) Use session_status() to check the session status to avoid repeated calls.

Configuring the session lifecycle in PHP can be achieved by setting session.gc_maxlifetime and session.cookie_lifetime. 1) session.gc_maxlifetime controls the survival time of server-side session data, 2) session.cookie_lifetime controls the life cycle of client cookies. When set to 0, the cookie expires when the browser is closed.


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

SecLists
SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

Zend Studio 13.0.1
Powerful PHP integrated development environment

VSCode Windows 64-bit Download
A free and powerful IDE editor launched by Microsoft

MantisBT
Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

Notepad++7.3.1
Easy-to-use and free code editor
