PHP handling of case-sensitive issues is messy, writing code may occasionally problem, so here to summarize.
But I'm not encouraging you to use these rules. We recommend that you always adhere to the "case sensitive" and follow the Uniform Code specification.
first, case sensitive
1. Variable names are case-sensitive
All variables are case-sensitive, including common variables as well as $_get, $_post, $_request, $_cookie, $_session, $GLOBALS, $_server, $_files, $_env, etc.;
Copy CodeThe 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 not found can change this default configuration item, solve)
Copy CodeThe code is as follows:
1 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 as File_uploads = 1
second, the case is not sensitive
4. The function name, method name, class name are not case-sensitive, but the same name as the definition is recommended
Copy CodeThe code is as follows:
Function Show () {
echo "Hello World";
}
Show (); Output Hello World recommended notation
SHOW (); Output Hello World
Copy CodeThe code is as follows:
Class cls{
static function func () {
echo "Hello World";
}
}
Cls::func (); Output Hello World
5. Magic constants are case-insensitive, recommended capitalization
Include: __line__, __file__, __dir__, __function__, __class__, __method__, __namespace__.
Copy CodeThe code is as follows:
Echo __line__; Output 2
Echo __line__; Output 3
6. NULL, TRUE, false case insensitive
Copy CodeThe 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 casting, case insensitive, including:
* (int), (integer) – Converted to integral type
* (BOOL), (Boolean) – converted to Boolean
* (float), (double), (real) – convert to floating-point type
* (String) – converted to a string
* (Array) – Convert an array
* (Object) – Convert to Object
Copy CodeThe 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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