In PHP, is
if(!$foo)
equivalent with
if($foo != true)
or with
if($foo !== true)
or is it even something completly different of both?
Note that,
== OR != compares the values of variables for equality, type casting as necessary. === OR !== checks if the two variables are of the same type AND have the same value.
This answer will give you better explanation of this concept:
https://stackoverflow.com/a/80649/3067928
if(!$foo)
is the equivalent to
if($foo != true)
so
$foo = null;
if(!$foo){
echo "asd";
}
will ouptut "asd"
Its not the same
!= is No equal (Returns true if is not equal)
!== is Not identical (Returns true if is not equal , or they are not of the same type)
$a != $b
TRUE if $a is not equal to $b after type juggling.
$a !== $b
TRUE if $a is not equal to $b, or they are not of the same type.
See type juggling in PHP for more info on type juggling.
Sources : php.net
Related
Why do these 2 statements not output the same result?
The only reason I can imagine is operator precedence which appears to the same for == and ===.
$a = (bool) 4 == 4;
$b = (bool) 4 === 4;
var_dump($a); // bool(true)
var_dump($b); // bool(false)
Yes, operator precedence is the same for == and ===. Clearly the difference here is the operator itself.
First we have to acknowledge that type casting has a higher precedence than these two comparison operators. So, in reality, you're doing:
$a = (TRUE == 4);
$b = (TRUE === 4);
When you do a == you're simply trying to see if the values are equal. Only values of the same type can be compared. Since you start with a boolean, the number 4 will therefore also be turned into a boolean. This is called type juggling. We already know that (bool)4 is TRUE. So $a must be TRUE.
However, when you do a === there is no type juggling, instead it will only return TRUE if the two operands have the same value and type. Since a boolean isn't the same type as an integer $b must be FALSE.
<?php
$test = "-3,-13";
if ($test == -3) {
echo "yay";
} else {
echo "nay";
}
?>
why it always runs through if condition and not going in else condition? I am new to php so do not know what's going on here.
The string is converted into an integer "-3, 46, blala" -> -3 , then the condition is evaluated.
Use the === operator to avoid conversion.
Most of the time, you do not want to let php do the conversion in your place (security problem). Rather, the request is refused.
As PHP documentation says
Example Name Result
$a == $b Equal TRUE if $a is equal to $b after type juggling.
$a === $b Identical TRUE if $a is equal to $b, and they are of the same type.
When we compare a number with a string, the string is converted to a number and the comparison performed numerically.
var_dump(0 == "a"); // 0 == 0 -> true
var_dump("1" == "01"); // 1 == 1 -> true
https://www.php.net/manual/en/language.operators.comparison.php
I saw
if($output !== false){
}
It's an exclamation mark with two equals signs.
It almost works like not equal. Does it has any extra significance?
They are the strict equality operators ( ===, !==) , the two operands must have the same type and value in order the result to be true.
For example:
var_dump(0 == "0"); // true
var_dump("1" == "01"); // true
var_dump("1" == true); // true
var_dump(0 === "0"); // false
var_dump("1" === "01"); // false
var_dump("1" === true); // false
More information:
PHP Comparison Operators
PHP’s === Operator enables you to compare or test variables for both equality and type.
So !== is (not ===)
!== checks the type of the variable as well as the value. So for example,
$a = 1;
$b = '1';
if ($a != $b) echo 'hello';
if ($a !== $b) echo 'world';
will output just 'world', as $a is an integer and $b is a string.
You should check out the manual page on PHP operators, it's got some good explanations.
See this question: How do the equality (==) and identity (===) comparison operators differ?.
'!==' is the strict version of not equal. I.e. it will also check type.
yes, it also checks that the two values are the same type. If $output is 0, then !== will return false, because they are not both numbers or booleans.
I have been programming in PHP for a while but I still dont understand the difference between == and ===. I know that = is assignment. And == is equals to. So what is the purpose of ===?
It compares both value and type equality.
if("45" === 45) //false
if(45 === 45) //true
if(0 === false)//false
It has an analog: !== which compares type and value inequality
if("45" !== 45) //true
if(45 !== 45) //false
if(0 !== false)//true
It's especially useful for functions like strpos - which can return 0 validly.
strpos("hello world", "hello") //0 is the position of "hello"
//now you try and test if "hello" is in the string...
if(strpos("hello world", "hello"))
//evaluates to false, even though hello is in the string
if(strpos("hello world", "hello") !== false)
//correctly evaluates to true: 0 is not value- and type-equal to false
Here's a good wikipedia table listing other languages that have an analogy to triple-equals.
It is true that === compares both value and type, but there is one case which hasn't been mentioned yet and that is when you compare objects with == and ===.
Given the following code:
class TestClass {
public $value;
public function __construct($value) {
$this->value = $value;
}
}
$a = new TestClass("a");
$b = new TestClass("a");
var_dump($a == $b); // true
var_dump($a === $b); // false
In case of objects === compares reference, not type and value (as $a and $b are of both equal type and value).
The PHP manual has a couple of very nice tables ("Loose comparisons with ==" and "Strict comparisons with ===") that show what result == and === will give when comparing various variable types.
It will check if the datatype is the same as well as the value
if ("21" == 21) // true
if ("21" === 21) // false
=== compares value and type.
== doesn't compare types, === does.
0 == false
evaluates to true but
0 === false
does not
Minimally, === is faster than == because theres no automagic casting/coersion going on, but its so minimal its hardly worth mentioning. (of course, I just mentioned it...)
It's a true equality comparison.
"" == False for instance is true.
"" === False is false
In PHP, ($myvariable==0)
When $myvariable is zero, the value of the expression is true; when $myvariable is null, the value of this expression is also true. How can I exclude the second case? I mean I want the expression to be true only when $myvariable is zero. Of course I can write
($myvariable != null && $myvariable == 0)
But is there other elegant way to do this?
$myvariable === 0
read more about comparison operators.
You hint at a deep question: when should an expression be true?
Below, I will explain why what you are doing isn't working and how to fix it.
In many languages null, 0, and the empty string ("") all evaluate to false, this can make if statements quite succinct and intuitive, but null, 0, and "" are also all of different types. How should they be compared?
This page tells us that if we have two variables being compared, then the variables are converted as follows (exiting the table at the first match)
Type of First Type of Second Then
null/string string Convert NULL to "", numerical/lexical comparison
bool/null anything Convert to bool, FALSE < TRUE
So you are comparing a null versus a number. Therefore, both the null and the number are converted to boolean. This page tells us that in such a conversion both null and 0 are considered FALSE.
Your expression now reads, false==false, which, of course, is true.
But not what you want.
This page provides a list of PHP's comparison operators.
Example Name Result
$a == $b Equal TRUE if $a equals $b after type juggling.
$a === $b Identical TRUE if $a equals $b, AND they are of the same type.
$a != $b Not equal TRUE if $a not equals $b after type juggling.
$a <> $b Not equal TRUE if $a not equals $b after type juggling.
$a !== $b Not identical TRUE if $a not equals $b, or they are not of the same type.
$a < $b Less than TRUE if $a is strictly less than $b.
$a > $b Greater than TRUE if $a is strictly greater than $b.
$a <= $b Less than/equal TRUE if $a is less than or equal to $b.
$a >= $b Greater than/equal TRUE if $a is greater than or equal to $b.
The first comparator is the comparison you are using now. Note that it performs the conversions I mentioned earlier.
Using the second comparator will fix your problem. Since a null and a number are not of the same type, the === comparison will return false, rather than performing type conversion as the == operator would.
Hope this helps.
To identify as null or zero by:
is_int($var) if a variable is a number or a numeric string. To identify Zero, use is_numeric($var) is also the solution or use $var === 0
is_null($var) if a variable is NULL
Try ($myvariable === 0) which will not perform type coercion.
Use the php function is_null( ) function along with the === operator. !== also works the way you'd expect.
The second solution wouldn't work either. The === operator is the solution to your problem.
If your zero could be a string, you should also considere checking the "zero string"
($myvariable === 0 || $myvariable === '0')
I hade faced a similar issue in one of my projects, with a minor difference that I was also using the values ZERO as a valid value for my condition. here's how I solved it using simple logic to separate NULL from zero and other values.
if (gettype($company_id) === 'NULL') {
$company = Company::where('id', Auth::user()->company_id)->first();
} else {
$company = Company::where('id', $company_id)->first();
}
$myvariable===0
$a === $b
Identical TRUE if $a is equal to $b, and they are of the same type
There's an is_null function, but this will just replace your $myvariable!=null
For my case i found this soulution and it works for me :
if ($myvariable === NULL) {
codehere...
}