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[phplearn]php从头开始学习1_PHP教程

时间：2021-07-01 10:21:17 帮助过：8人阅读

[php learn] php 从头开始学习1

前言：大概在2006年的时候，学习过一段时间的php，并且当时做了一个下载的网站，后来由于读研究生阶段用的是java、j2ee相关，所以php就搁浅掉了，php这些年也发生了很大的变化，最大一个变化是支持面向对象了。

现在由于需要php做些东西，再次学习，从头开始！

Local和Global作用域：函数之外声明的变量拥有global作用域，只能在函数之外访问
PHP global关键字 global关键字用与访问函数外的全局变量 function myTest() { global $x,$y; $y=$x+$y;
}
myTest(); echo $y; ?>
PHP同时在名为$GLOBALS[index]的数组中存储了所有的全局变量。下标存为变量名，这个数组在函数内也可以访问，并且能够用于直接更新全局变量。
上面的例子可以重写为： function myTest() { $GLOBALS['y']=$GLOBALS['x']+$GLOBALS['y']; }
myTest(); echo $y;
?>

echo 和 print 之间的差异：

echo - 能够输出一个以上的字符串

print - 只能输出一个字符串，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 - 它使用三个参数：

首个参数定义常量的名称
第二个参数定义常量的值

可选的第三个参数规定常量名是否对大小写敏感。默认是 false。

常量输出不用带$

运算符	名称	例子	结果
==	等于	$x == $y	如果 $x 等于 $y，则返回 true。
===	全等（完全相同）	$x === $y	如果 $x 等于 $y，且它们类型相同，则返回 true。
!=	不等于	$x != $y	如果 $x 不等于 $y，则返回 true。
<>	不等于	$x <> $y	如果 $x 不等于 $y，则返回 true。
!==	不全等（完全不同）	$x !== $y	如果 $x 不等于 $y，且它们类型不相同，则返回 true。
>	大于	$x > $y	如果 $x 大于 $y，则返回 true。
<	大于	$x < $y	如果 $x 小于 $y，则返回 true。
>=	大于或等于	$x >= $y	如果 $x 大于或者等于 $y，则返回 true.
<=	小于或等于	$x <= $y	如果 $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

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

foreach ($colors as $value) {
echo "$value
";
}
?>

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

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 someone@w3schools.com)
$_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

_REQUEST

Example

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

空格符

用于匹配字母，数字或下划线字符

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[phplearn]php从头开始学习1_PHP教程