Some non-predefined arrays in php

In PHP development, predefined arrays are one of the data structures often used by programmers. Predefined arrays in PHP are represented by a special character in front of the variable name. For example: $_GET, $_POST, and $_COOKIE are all PHP predefined arrays. However, sometimes we encounter arrays that are not PHP's predefined arrays. How should we deal with these unusual arrays? This article will introduce you to some non-predefined arrays.

1. $GLOBALS
   $GLOBALS is a global variable array that contains references to all global variables in the script. This means that $GLOBALS can be used from anywhere to access any global variable. For example:

$var1 = 'Hello';
$var2 = 'World';

function myFunc() {
    echo $GLOBALS['var1'] . ' ' . $GLOBALS['var2'];
}

myFunc(); // 输出：Hello World

2. $HTTP_RAW_POST_DATA
   This array contains the original POST request data. Before PHP 5.6, when using the HTTP protocol to submit data, this array can directly obtain the data submitted in the POST request. However, starting from PHP 5.6 version, this array has been deprecated. If you need to get POST request data, you should use the $_POST array.
3. $http_response_header
   This array contains the response header information of the HTTP request and is generally used to obtain the status code of the HTTP request. For example:

$fileContent = file_get_contents('http://www.example.com/');
print_r($http_response_header);

// 输出：
// Array
// (
//     [0] => HTTP/1.1 200 OK
//     [1] => Date: Thu, 23 Sep 2021 13:28:50 GMT
//     [2] => Server: Apache
//     [3] => X-Powered-By: PHP/7.4.23
//     ...
// )

4. $argv and $argc
   are two arrays used to obtain the command line parameters passed to the PHP script when it is started. The $argc array contains the number of parameters, and the $argv array contains the parameter list. For example, execute the following script on the command line:

php myScript.php arg1 arg2 arg3

In the script, you can obtain parameter information through $argc and $argv:

<?php
// myScript.php
echo "参数个数：" . $argc . "\n";
echo "参数列表：";
print_r($argv);
?>

Output:

参数个数：4
参数列表：Array
(
    [0] => myScript.php
    [1] => arg1
    [2] => arg2
    [3] => arg3
)

5. $php_errormsg
   This array contains the error message that triggered the latest error. For example:

$fileHandle = fopen('not-exist-file.txt', 'r');
if (!$fileHandle) {
    echo $php_errormsg;
}

Output: "fopen(not-exist-file.txt): failed to open stream: No such file or directory"

Summary
The above is PHP Some non-predefined arrays in include: $GLOBALS, $HTTP_RAW_POST_DATA, $http_response_header, $argv, $argc, and $php_errormsg. Understanding the purpose of these arrays can help us better program PHP.

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