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:
如需设置常量,请使用 define() 函数 - 它使用三个参数:
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 <> | 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 <=>=> | 如果 $x 小于或者等于 $y,则返回 true。 |
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:
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 $_post is widely used to collect form data after submitting an html form with method="post". $_post is also widely used to pass variables.
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