PHP Case PROBLEM: function name and class name are not distinguished, variable names distinguish _php skills

PHP for case sensitive problem processing is messy, write code may occasionally problem, so here is summed up.
But I am not encouraging everyone to use these rules. We recommend that you always adhere to the "case sensitive", follow the Uniform Code specifications.

1. Variable names are case-sensitive

Copy Code code 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 as uppercase
(but could not find a way to change this default configuration item, solve)

Copy Code code as follows:

<?php
Define ("ABC", "Hello World");
Echo ABC; Output Hello World
ECHO ABC; Output ABC

3. PHP.ini configuration item directives are case-sensitive
such as File_uploads = 1 cannot be written file_uploads = 1

4. Function name, method name, class name is case-insensitive
But it is recommended to use the same name as the definition

Copy Code code as follows:

<?php
Function Show () {
echo "Hello World";
}

Show (); Output Hello World recommended notation

Show (); Output Hello World

Copy Code code as follows:

<?php
Class cls{
static function func () {
echo "Hello World";
}
}
Cls::func (); Output Hello World

5. Magic constant case-insensitive, recommended uppercase
Include: __line__, __file__, __dir__, __function__, __class__, __method__, __namespace__.

Copy Code code as follows:

<?php
Echo __line__; Output 2
Echo __line__; Output 3

6. NULL, TRUE, false is case-insensitive

Copy Code code as follows:

<?php
$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, function names are case-insensitive, and are often overlooked in small details by novices, as tested below.

PHP variable name case sensitivity test:

Copy Code code as follows:

<?php
$AAA = "Jb51.net";
$AAA = "JB51." CN ";
echo $aaa. '-'. $AAA; jb51.net-jb51.cn
?>

PHP function name does not match case test:

Copy Code code as follows:

<?php
function bbb () {
Echo ' abc ';
}
function BBB () {
echo "ABC";
}
?>

The above code will be an error: (!) Fatal error:cannot redeclare BBB ()