Update: 0 isn't using the default value, after testing it was the condition that was failing as suggested by the answers.
function test($value='A') {
if ($value != 'A') {
echo 'OK';
}
else {
echo 'NOT OK';
}
}
test(); // Outputs NOT OK
test('A'); // Outputs NOT OK
test(0); // Outputs NOT OK, Should output OK?
test('0'); // Outputs OK
test(null); // Outputs OK
test(false); // Outputs OK
This is kind of throwing one of my functions. I was surprised to see only 0 does this and null works fine. Does anyone know why PHP is interpreting 0 as the default value?
In PHP, comparing a string 'A' with a number 0 causes a change of the string to a number. In this case 'A' gets converted to 0, so of course 0 == 0.
See here for details.
For completeness, the fix, from the same linked documentation is
use strict comparison operators (===, !==)
comparison operators
Change your test to:
if ($value !== 'A') {
When you use == or != to compare a number and a string, it coerces the string to a number. The string 'A' converts to 0, so they're equal.
As you using loosely comparison operator PHP is trying to implicitly convert the 0 into the string. Use !== for strict comparison.
DEMO.
Related
Why below code is printing the "here", it should be "there"
$a = "171E-10314";
if($a == '0')
{
echo "here";
}
else
{
echo "there";
}
PHP automatically parses anything that's a number or an integer inside a string to an integer. "171E-10314" is another way of telling PHP to calculate 171 * 10 ^ -10314, which equates to (almost) 0. So when you do $a == '0', the '0' will equate to 0 according to PHP, and it returns true.
If you want to compare strings, use the strcmp function or use the strict comparator ===.
when you use the == comparison, PHP tries to cast to different data types to check for a match like that
in your case:
'0' becomes 0
"171E-10314" is still mathematically almost 0 but I think PHP just rounds it to 0 due to the resolution of float.
check this link for a visual representation:
http://www.wolframalpha.com/input/?i=171E-10314
As per the answers given I tried to convert the string into numerical:
$a = "171E-10314" + 0;
print $a;
And I got output as 0.
Thats why it is printing here.
Use === /*(this is for the 30 character)*/
PHP is thinking that null is 0 when the character in $position doesn't exist.
$statusentery = $_POST[status];
$position = strpos($statusentery,"<");
if ($position == 0){
echo "Sorry, for security purposes we do not
allow characters such as <";
exit;
}
For example, if $statusentery was equal to "Howdy there", it would return "Sorry, for security purposes we do not allow characters such as <". (unexpected)
If $statusentery was equal to "Howdy there <" it would return blank (expected).
How to make it work so that when I enter "Howdy there", it didn't do the if loop, but when I enter "< howdy there>", it did the if loop?
Because 0 can means "false" in PHP, $postition will be false when it doesn't exist. So you'll need to use the following:
if ($position === 0){
Using the triple equal sign in PHP verifies that the compared values have the same data type. A lot more information can be found here: http://php.net/manual/en/language.operators.comparison.php
From: http://php.net/manual/es/function.strpos.php
WARNING
As strpos may return either FALSE (substring absent) or 0 (substring
at start of string), strict versus loose equivalency operators must be
used very carefully.
To know that a substring is absent, you must use:
=== FALSE
To know that a substring is present (in any position including 0), you
can use either of:
!== FALSE (recommended)
-1 (note: or greater than any negative number)
To know that a substring is at the start of the string, you must use:
=== 0
To know that a substring is in any position other than the start, you
can use any of:
0 (recommended) != 0 (note: but not !== 0 which also equates to FALSE) != FALSE (disrecommended as highly confusing)
Also note that you cannot compare a value of "" to the returned value
of strpos. With a loose equivalence operator (== or !=) it will return
results which don't distinguish between the substring's presence
versus position. With a strict equivalence operator (=== or !==) it
will always return false.
So the code must be:
$statusentery = $_POST[status];
$position = strpos($statusentery,"<");
if ($position === 0){
echo "Sorry, for security purposes we do not allow characters such as <";
exit;
}
This is a tricky function. As stated in the strpos manual:
Warning This function may return Boolean false, but may also return a
non-Boolean value which evaluates to false. Please read the section on
Booleans for more information. Use the === operator for testing the
return value of this function.
I use this comparison, which works well without even a notice level warning:
if ($position > -1)
Returns boolean false when the string is not found, which is evaluable as a number, thus comparing whether the value is greater than -1 actually works well. In case any match is found, even at position 0 the above comparison will be passed.
Why does PHP return 0 when a logical AND returns FALSE, but does not return the 0 when a conditional AND returns FALSE? Witness:
php > function a(){
php { echo "a";
php { return FALSE;
php { }
php > function b(){
php { echo "b";
php { return TRUE;
php { }
php > echo (a() && b())."\n";
a
php >
php > echo (a() & b())."\n";
ab0
php >
Notice that the second echo statement ends with 0, yet the first does not. Why?
&& returns a boolean. The boolean false when cast to a string is '', an empty string.
& is a bitwise and (not a "conditional and", whatever that is), which produces a number (or binary blob, depending on the arguments) as a result. In this case, the operation results in the number 0.
In second case
php > echo (aa() & b())."\n";
is a bitwise AND. You need to use && for comparison
Actually, neither of the answers provided are fully correct. The right answer is threefold.
The "problem" here is that && is a short-circuit operator. So it basically moves from the left-most argument to the right most one-by-one. For each one it checks if it returns true, if not, it stops and WILL NOT execute the next statement. PHP Documentation on logical operators.
Ergo: in the first case, you see only a (and not b) due to shortcircuiting. Then you also don't see the 0 because it's a boolean (not an int).
Then in the 2nd case you see an integer 0 because he's using a bitwise AND instead of a logical.
Can anyone figure out why this might happen in PHP (am using v5.4):
$value = 0;
$existing_value = "Unknown";
if ($value == $existing_value) {
echo "$value == $existing_value";
} else {
echo "$value != $existing_value";
}
This outputs as 0 == Unknown
Interestingly, $value = "0" (i.e. set as a string), evaluates to be false
Is this a known behaviour? Have I missed something in the documentation on this? Debugging this was driving me crazy earlier today!
Thanks for your help in advance...
This is caused by the automatic type casting, PHP uses.
When comparing an int value with a string using just ==, the string will be casted to an int, which in your case results in a 0 and hence a true evaluation.
See the respective PHP documentation for more information.
To circumvent this, you could use === instead of ==. The former includes a type check, which will make your condition evaluate to false:
$value = 0;
$existing_value = "Unknown";
if ($value === $existing_value) {
echo "$value === $existing_value";
} else {
echo "$value !== $existing_value";
}
When you compare a number with a string in PHP, as you do here, the string is converted to a number. Since the string "Unknown" is not numeric, it's converted to the number 0.
If you check for equality with the === operator, it won't perform type conversion and it'll evaluate as false.
http://php.net/manual/en/language.operators.comparison.php
You should have a look at the comparison tables in PHP Especially the loose comparison (using ==) section as compared to the strict comparison (using ===) section.
this is code:
$s = 0;
$d = "dd";
if ($s == $d) {
var_dump($s);
die(var_dump($d));
}
result is:
int 0
string 'dd' (length=2)
Please explain why.
why ($s == $d) results as true?
Of course, if === is used it will results as false but why this situation requires ===?
Shouldn't it be returned false in both situations?
Because (int)$d equals with 0 and 0=0
you must use strict comparison === for different character tyes (string) with (int)
Your $d is automatically converted to (int) to have something to compare.
When you compare a number to a string, the string is first type juggled into a number. In this case, dd ends up being juggled into 0 which means that it equates to true (0==0).
When you change the code to:
<?php
$s = 1;
$d = "dd";
if ($s == $d)
{
var_dump($s);
die(var_dump($d));
}
?>
You will find that it doesn't pass the if statement at all.
You can more details by reading up on comparison operators and type juggling.
The string "dd" is converted to int, and thus 0.
Another example :
if ( "3kids" == 3 )
{
return true;
}
And yes, this returns true because "3kids" is converted to 3.
=== does NOT auto convert the items to the same type.
Also : 0 == false is correct, but 0 === false is not.
See : http://php.net/manual/en/language.types.type-juggling.php
The string will try to parsed into a number, returns 0 if it is not in right number format.
As seen in the php website :
http://php.net/manual/en/language.operators.comparison.php
var_dump(0 == "a"); // 0 == 0 -> true
In PHP, == should be pronounce "Probably Equals".
When comparing with ==, PHP will juggle the file-types to try and find a match.
A string with no numbers in it, is evaluated to 0 when evaluated as an int.
Therefore they're equals.