This question already has answers here:
php - Why can't you define a constant named EMPTY
(4 answers)
Closed 4 years ago.
Could you please tell me why this code throws a parse error if the name of the constant is EMPTY, but if I change it to EMPTY2 or SUBSTR it does work.
define('EMPTY', '');
if (empty(EMPTY)) {
echo 'hello world';
}
Because, as stated in this Quora answer, PHP function names are case-insensitive, so EMPTY collides with the built-in function empty().
PHP manual mentions this in a small note right after Example #3 in the subsection about User-defined functions:
Note: Function names are case-insensitive, though it is usually good form to call functions as they appear in their declaration.
Related
This question already has answers here:
Reference Guide: What does this symbol mean in PHP? (PHP Syntax)
(24 answers)
Closed 7 years ago.
I want to know about meaning of $$val; what is the actual meaning is?i tried to find meaning of this in google but not understand properly. Please help me in this situations.
For example: suppose i have one variable which has $$value;
meaning of $$value?
You didn't put the language, but I'll assume you mean PHP
That's a variable variable.
That means you ware asking for the value of the variable whose name.is the first variable.
Here's an example, since that's quite confusing:
$foo = "Hi";
$bar = "world";
$world = "Hello!";
echo $$bar; // "Hello!"
php fiddle: http://ideone.com/Ve4YOO
Reference: https://secure.php.net/manual/en/language.variables.variable.php
This question already has answers here:
What does it mean to start a PHP function with an ampersand?
(3 answers)
Closed 7 years ago.
I'm using a CMS package written in PHP. In one of it's core files I saw following line that is for defining a function in a class body.
public static function &getLib($sClass, $aParams = array()) {
// Code
}
I didn't understand why the function name 'getLib' has been prepended with the ampersand(&) sign? I've never seen such thing before.
Can someone please explain me in detail why such thing has been done and what's the benefit it has over simply using the function name?
It means the function should return a reference to a variable rather than just the value itself.
This question already has answers here:
Does function definition order matter?
(7 answers)
Closed 1 year ago.
The following code runs in PHP
<?php
$foo = "Chocolate milkshake";
go($foo);
function go($param) {
echo $param;
}
?>
// Output: chocolate milkshake
See this Demo http://codepad.viper-7.com/ToApZa
This code runs without errors and prints specified output, why?
I thought this "function hoisting" only occurred in JavaScript
It doesn't matter where you declare your functions in PHP in most cases, as you've just proved :)
Take a look at this page for more details. The key point:
Functions need not be defined before they are referenced, except when a function is conditionally defined as shown in the two examples below.
This question already has answers here:
Reference Guide: What does this symbol mean in PHP? (PHP Syntax)
(24 answers)
Closed 8 years ago.
Can you please explain to me the differences between two functions:
function &a(){
return something;
}
and
function b(){
return something;
}
Thanks!
The first returns a reference to something, the second a copy of something.
In first case, when the caller modify the returned value, something will be modified as a global variable do.
In the second case, modifying a copy as no effect to the source.
An ampersand before a function name means the function will return a reference to a variable instead of the value.
According to this LINK
Returning by reference is useful when you want to use a function to find to which
variable a reference should be bound. Do not use return-by-reference to increase
performance. The engine will automatically optimize this on its own. Only return
references when you have a valid technical reason to do so.
This question already has answers here:
What is the difference between a language construct and a "built-in" function in PHP?
(4 answers)
Closed 8 years ago.
PHP has a large number of batteries-included functions, e.g. functions on arrays. Some of these, like each, are present in get_defined_functions()['internal']. Others, like reset and many others, are not present at all. However, they are treated as functions in every other way: they are not documented as "language constructs" or keywords; I can call them using the "variable function" feature; function_exists("reset") returns true; if I try to redefine them (e.g. function reset() { ... }), I get an error about redeclaration, rather than a syntax error; and so on.
Why are these functions not listed by get_defined_functions? Are they not actually functions? If not, what are they? If they are functions, then what actually is it that get_defined_functions is listing? In either case, how do I list the things that don't appear in get_defined_functions?
Quite a short answer: Reset is present in get_defined_functions()['internal'].
Look at [1532] in this fiddle: http://phpfiddle.org/main/code/h5n-ndx