PHP case problem: function names and class names are not distinguished, variable names are distinguished_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. Variable names are case-sensitive

Copy code The code is as follows:

$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 code The code is as follows:

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

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, uppercase letters are recommended
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

PHP variable names are case-sensitive, while function names are not case-sensitive. This is a small detail that is often overlooked by novices. The test is as follows.

PHP variable name case sensitivity test:

Copy code The code is as follows:

$aaa = "jb51.net";
$AAA = "JB51.CN";
echo $aaa.'-'.$AAA; //jb51.net-JB51.CN
?>

PHP function name case-insensitive test:

Copy code The code is as follows:

function bbb(){
echo 'abc ';
}
function BBB(){
echo "Abc";
}
?>

The above code will report an error: ( ! ) Fatal error: Cannot redeclare BBB()

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