PHP study notes_5_Arrays and predefined variables (unfinished)

php has two types of arrays: index array and associative array. Their declaration methods are similar. There are mainly three declaration methods:

Declaration method:
array(); can declare any array, see the example below

<code><?php
    $temp= array(<span>1</span>,<span>2</span>,<span>3</span>);
    print_r($temp);<span>//这是打印数组的方法</span><span>/**
    输出的结果，Array90

    **/</span></code>

Note:
1. When null is used as a data key, it will be converted into an empty string;
2. When adding a value, the array subscript is the current maximum subscript plus 1. If the maximum subscript value is a negative number, when adding an element with an unspecified index, the index is 0;
3.

<code><span>$_POST</span>：接收表单以POST发送的数据
<span>$_GET</span>：接收表单以GET方式发送的数据
<span>$_REQUEST</span>：<span>$_GET</span>+<span>$_POST</span>+<span>$_COOKIE</span><span>$_FILES</span>：HTTP文件上传变量
<span>$_SERVER</span>：服务器与执行环境变量
<span>$_ENV</span>：环境变量
<span>$_SESSION</span>：会话变量
<span>$_COOKIE</span>：http cookie
<span>$_GLOBALE</span>:预定义变量的总集合
<span>$php_errormsg</span>：前一个错误信息（只在错误发生的作用域内可用，需要开启php.ini里track_error配置项）</code>

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