[php learn] php 从头開始学习1

Posted 2020-09-27 cxchanpin

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前言：大概在2006年的时候，学习过一段时间的php。而且当时做了一个下载的站点，后来因为读研究生阶段用的是java、j2ee相关，所以php就搁浅掉了，php这些年也发生了非常大的变化，最大一个变化是支持面向对象了。

如今因为须要php做些东西，再次学习，从头開始！

Local和Global作用域：

函数之外声明的变量拥有global作用域。仅仅能在函数之外訪问

PHP globalkeyword

globalkeyword用与訪问函数外的全局变量

php

$x=5;

$y=10;

function myTest()

{

global $x,$y;

$y=$x+$y;

}

myTest();

echo $y;

PHP同一时候在名为$GLOBALS[index]的数组中存储了全部的全局变量。

下标存为变量名，这个数组在函数内也可以訪问，而且可以用于直接更新全局变量。

上面的样例能够重写为：

php

$x=5;

$y=10;

function myTest()

{

$GLOBALS[‘y‘]=$GLOBALS[‘x‘]+$GLOBALS[‘y‘];

}

myTest();

echo $y;

echo 和 print 之间的差异：

echo - 可以输出一个以上的字符串
print - 仅仅能输出一个字符串。并始终返回 1

var_dump()函数会返回变量的数据类型和值。

设置 PHP 常量

如需设置常量。请使用 define() 函数 - 它使用三个參数：

首个參数定义常量的名称
第二个參数定义常量的值
可选的第三个參数规定常量名是否对大写和小写敏感。默认是 false。

<?php
define("GREETING", "Welcome to W3School.com.cn!");
echo GREETING;
?>

常量输出不用带$

运算符	名称	样例	结果
==	等于	$x == $y	假设 $x 等于 $y，则返回 true。
===	全等（全然同样）	$x === $y	假设 $x 等于 $y，且它们类型同样，则返回 true。
!=	不等于	$x != $y	假设 $x 不等于 $y，则返回 true。
<>	不等于	$x <> $y	假设 $x 不等于 $y。则返回 true。
!==	不全等（全然不同）	$x !== $y	假设 $x 不等于 $y，且它们类型不同样，则返回 true。
>	大于	$x > $y	假设 $x 大于 $y，则返回 true。
<	大于	$x < $y	假设 $x 小于 $y，则返回 true。
>=	大于或等于	$x >= $y	假设 $x 大于或者等于 $y，则返回 true.
<=	小于或等于	$x <= $y	假设 $x 小于或者等于 $y，则返回 true。

数组：

#array
$car=array("Volvo","BWM","Jeep");
var_dump($car);

结果：

array(3) { [0]=> string(5) "Volvo" [1]=> string(3) "BWM" [2]=> string(4) "Jeep" }

foreach:

Syntax

foreach ($array as $value) {

  code to be executed;

}

Example

<?
php 

$colors = array("red","green","blue","yellow"); 

foreach ($colors as $value) {

  echo "$value <br>";

}

?
>

PHP Global Variables - Superglobals

Several predefined variables in PHP are "superglobals", which means that they are always accessible, regardless of scope - and you can access them from any function, class or file without having to do anything special.

The PHP superglobal variables are:

$GLOBALS
$_SERVER
$_REQUEST
$_POST
$_GET
$_FILES
$_ENV
$_COOKIE
$_SESSION

$_SERVER[‘HTTP_REFERER‘]:

HTTP Referer是header的一部分，当浏览器向webserver发送请求的时候。通常会带上Referer。告诉server我是从哪个页面链接过来的，server籍此能够获得一些信息用于处理。

Element/Code	Description
$_SERVER[‘PHP_SELF‘]	Returns the filename of the currently executing script
$_SERVER[‘GATEWAY_INTERFACE‘]	Returns the version of the Common Gateway Interface (CGI) the server is using
$_SERVER[‘SERVER_ADDR‘]	Returns the IP address of the host server
$_SERVER[‘SERVER_NAME‘]	Returns the name of the host server (such as www.w3schools.com)
$_SERVER[‘SERVER_SOFTWARE‘]	Returns the server identification string (such as Apache/2.2.24)
$_SERVER[‘SERVER_PROTOCOL‘]	Returns the name and revision of the information protocol (such as HTTP/1.1)
$_SERVER[‘REQUEST_METHOD‘]	Returns the request method used to access the page (such as POST)
$_SERVER[‘REQUEST_TIME‘]	Returns the timestamp of the start of the request (such as 1377687496)
$_SERVER[‘QUERY_STRING‘]	Returns the query string if the page is accessed via a query string
$_SERVER[‘HTTP_ACCEPT‘]	Returns the Accept header from the current request
$_SERVER[‘HTTP_ACCEPT_CHARSET‘]	Returns the Accept_Charset header from the current request (such as utf-8,ISO-8859-1)
$_SERVER[‘HTTP_HOST‘]	Returns the Host header from the current request
$_SERVER[‘HTTP_REFERER‘]	Returns the complete URL of the current page (not reliable because not all user-agents support it)
$_SERVER[‘HTTPS‘]	Is the script queried through a secure HTTP protocol
$_SERVER[‘REMOTE_ADDR‘]	Returns the IP address from where the user is viewing the current page
$_SERVER[‘REMOTE_HOST‘]	Returns the Host name from where the user is viewing the current page
$_SERVER[‘REMOTE_PORT‘]	Returns the port being used on the user‘s machine to communicate with the web server
$_SERVER[‘SCRIPT_FILENAME‘]	Returns the absolute pathname of the currently executing script
$_SERVER[‘SERVER_ADMIN‘]	Returns the value given to the SERVER_ADMIN directive in the web server configuration file (if your script runs on a virtual host, it will be the value defined for that virtual host) (such as [email protected])
$_SERVER[‘SERVER_PORT‘]	Returns the port on the server machine being used by the web server for communication (such as 80)
$_SERVER[‘SERVER_SIGNATURE‘]	Returns the server version and virtual host name which are added to server-generated pages
$_SERVER[‘PATH_TRANSLATED‘]	Returns the file system based path to the current script
$_SERVER[‘SCRIPT_NAME‘]	Returns the path of the current script
$_SERVER[‘SCRIPT_URI‘]	Returns the URI of the current page

PHP $_REQUEST

PHP $_REQUEST is used to collect data after submitting an html form.

Example

<html>

<body>

<form method="post" action="<?
php echo $_SERVER[‘PHP_SELF‘];?>">

Name: <input type="text" name="fname">

<input type="submit">

</form>

<?php 

$name = $_REQUEST[‘fname‘]; 

echo $name; 

?>

</body>

</html>

PHP $_POST

PHP $_POST is widely used to collect form data after submitting an HTML form with method="post". $_POST is also widely used to pass variables.

Example

<html>

<body>

<form method="post" action="<?php echo $_SERVER[‘PHP_SELF‘];?>">

Name: <input type="text" name="fname">

<input type="submit">

</form>

<?php 

$name = $_POST[‘fname‘]; 

echo $name; 

?>

</body>
</html>