Sorting out case-sensitive issues in PHP_PHP tutorial

PHP's handling of case-sensitive issues is messy, and problems may occasionally occur when writing code, so I'll summarize it here.
But I am not encouraging everyone to use these rules. It is recommended that everyone always adhere to "case sensitivity" and follow unified coding standards.
1. Case sensitivity
1. Variable names are case-sensitive
All variables are case-sensitive, including ordinary variables and $_GET, $_POST, $_REQUEST, $_COOKIE , $_SESSION, $GLOBALS, $_SERVER, $_FILES, $_ENV, etc.;

Copy code The code is as follows:

< ;?php
$abc = 'abcd';
echo $abc; //output 'abcd'
echo $aBc; //no output
echo $ABC; //no output

2. Constant names are case-sensitive by default and are usually written in uppercase
(but I couldn’t find a configuration item that can change this default, please solve)

Copy the code The code is as follows:

1 define("ABC","Hello World");
echo ABC; //Output Hello World
echo abc; //Output abc

3. php.ini configuration item instructions are case-sensitive
For example, file_uploads = 1 cannot be written as File_uploads = 1
two , case-insensitive
4. Function names, method names, and class names are not case-sensitive, but it is recommended to use the same name as when defined

Copy code The code is as follows:

function show(){
echo "Hello World";
}
show(); / /Output Hello World Recommended writing method
SHOW(); //Output Hello World

Copy code The code is as follows:

class cls{
static function func(){
echo "hello world";
}
}
Cls::FunC( ); //Output hello world

5. Magic constants are not case-sensitive. It is recommended to use uppercase letters
including: __LINE__, __FILE__, __DIR__, __FUNCTION__, __CLASS__, __METHOD__, __NAMESPACE__.

Copy code The code is as follows:

echo __line__; //Output 2
echo __LINE__; //Output 3

6. NULL, TRUE and FALSE are not case sensitive

Copy code The code is as follows:

$a = null;
$b = NULL;
$c = true;
$d = TRUE;
$e = false;
$f = FALSE;
var_dump($a == $b); //Output boolean true
var_dump($c == $d); //Output boolean true
var_dump ($e == $f); //Output boolean true

7. Type coercion, case-insensitive, including:
* (int), (integer) – converted to Integer type
* (bool), (boolean) – converted to Boolean type
* (float), (double), (real) – converted to floating point type
* (string) – converted to character String
* (array) – converted to array
* (object) – converted to object

Copy code The code is as follows:

$a=1;
var_dump($a); //Output int 1
$b=(STRING)$a;
var_dump($b ); //Output string '1' (length=1)
$c=(string)$a;
var_dump($c); //Output string '1' (length=1)

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