Diese Seite bei php.net
The PHP manual text and comments are covered by the Creative Commons Attribution 3.0 License © the PHP Documentation Group - Impressum - mail("TO:Reinhard Neidl",...)
Vergleichs-Operatoren erlauben es - wie der Name schon sagt - zwei Werte zu vergleichen. Wenn Sie an Beispielen verschiedener auf Typen bezogener Vergleiche interessiert sind, können Sie sich PHP type comparison tables anschauen.
| Beispiel | Name | Ergebnis |
|---|---|---|
| $a == $b | Gleich | Gibt TRUE zurück, wenn $a gleich $b ist. |
| $a === $b | Identisch | Gibt TRUE zurück wenn $a gleich $b ist und beide vom gleichen Typ sind (eingeführt in PHP 4). |
| $a != $b | Ungleich | Gibt TRUE zurück, wenn $a nicht gleich $b ist. |
| $a <> $b | Ungleich | Gibt TRUE zurück, wenn $a nicht gleich $b ist. |
| $a !== $b | Nicht identisch | Gibt TRUE zurück, wenn $a nicht gleich $b ist, oder wenn beide nicht vom gleichen Typ sind (eingeführt in PHP 4). |
| $a < $b | Kleiner Als | Gibt TRUE zurück, wenn $a kleiner als $b ist. |
| $a > $b | Größer Als | Gibt TRUE zurück, wenn $a größer als $b ist. |
| $a <= $b | Kleiner Gleich | Gibt TRUE zurück, wenn $a kleiner oder gleich $b ist. |
| $a >= $b | Größer Gleich | Gibt TRUE zurück, wenn $a größer oder gleich $b ist. |
Ein weiter Vergleichs-Operator ist der "?:"- oder Trinitäts-Operator.
<?php
// Beispielanwendung für den Trinitäts-Operator
$action = (empty($_POST['action'])) ? 'standard' : $_POST['action'];
// Obiges ist mit dieser if/else-Anweisung identisch
if (empty($_POST['action'])) {
$action = 'standard';
} else {
$action = $_POST['action'];
}
?>
Siehe auch strcasecmp(), strcmp(), Array-Operatoren und den Abschnitt über Typen.
Replying to the comment on Aug 6, 2010, the comparisons return TRUE because they are recognized as numerical strings and are converted to integers. If you try "abc" == " abc", it will return FALSE as expected. To avoid the type conversions, simply use the identity operator (===).
I discover after 10 years of PHP development something awfull : even if you make a string comparison (both are strings), strings are tested like integers and leading "space" character (even \n, \r, \t) is ignored ....
I spent hours because of leading \n in a string ... it hurts my developper sensibility to see two strings beeing compared like integers and not like strings ... I use strcmp now for string comparison ... so stupid ...
Test code :
<?php
test("1234", "1234");
test("1234", " 1234");
test("1234", "\n1234");
test("1234", "1234 ");
test("1234", "1234\n");
function test($v1, $v2) {
echo "<h1>[".show_cr($v1)."] vs [".show_cr($v2)."]</h1>";
echo my_var_dump($v1)."<br />";
echo my_var_dump($v2)."<br />";
if($v1 == $v2) {
echo "EQUAL !";
}
else {
echo "DIFFERENT !";
}
}
function show_cr($var) {
return str_replace("\n", "\\n", $var);
}
function my_var_dump($var) {
ob_start();
var_dump($var);
$dump = show_cr(trim(ob_get_contents()));
ob_end_clean();
return $dump;
}
?>
Displays this ->
[1234] vs [1234]
string(4) "1234"
string(4) "1234"
EQUAL !
[1234] vs [ 1234]
string(4) "1234"
string(5) " 1234"
EQUAL !
[1234] vs [\n1234]
string(4) "1234"
string(5) "\n1234"
EQUAL !
[1234] vs [1234 ]
string(4) "1234"
string(5) "1234 "
DIFFERENT !
[1234] vs [1234\n]
string(4) "1234"
string(5) "1234\n"
DIFFERENT !
I prefer writing (!$a == 'hello') much more than ($a != 'hello'), but I wondered about the performance.
So I did a benchmark:
<?php
for($bench = 0; $bench < 3; $bench++)
{
$start = microtime(true);
$a = 1;
for($i = 0; $i < 100000000; $i++)
{
if(!$a == 'hello') $b++;
}
$end = microtime(true);
echo "Used time: " . ($end-$start) . "\n";
}
?>
and it results with
# if($a != 'hello')
Used time: 12.552895069122
Used time: 12.548940896988
Used time: 12.470285177231
# if(!$a == 'hello')
Used time: 7.6532161235809
Used time: 7.6426539421082
Used time: 7.6452689170837
I am posting another hint about formatting of conditional expression blocks. It does take more lines, but lines starting with "?" and ":" allow to distinguish ternary operator quite quickly.
<?php
// Single ternary operator
$sentence = $value == 1
? 'You have one egg.'
: 'You have '.$value.' eggs.';
// Nested ternary operators
$sentence = $value == 1
? 'You have one egg.'
: ($value == 0
? 'You have no eggs.'
($value == 2
? 'You have two eggs.'
: 'You have '.$value.' eggs.'
);
?>
PS: In case on wondering about concatenation "." operator inside the expression: concatenation has higher priority than ternary operator, so it is evaluated first.
a function to help settings default values, it returns its own first non-empty argument :
make your own eor combos !
<?php
/*
* Either Or
*
* usage: $foo = eor(test1(),test2(),"default");
* usage: $foo = eor($_GET['foo'], foogen(), $foo, "bar");
*/
function eor() {
$vars = func_get_args();
while (!empty($vars) && empty($defval))
$defval = array_shift($vars);
return $defval;
}
?>
Boolean switch usege
<?php
class User_Exception extends Exception{}
class User{
public function register($login,$pass,$passCheck)
switch(false){
case(strlen($pass) >= 5):
throw new User_Exception("Password must be at last 5 chars length");
case($pass == $passCheck):
throw new User_Exception("Password is not confirmed!");
case(strlen($login) >= 5):
throw new User_Exception("Login must be at last 5 chars length");
//Do other checks
default:
//Do registration
return true;
}
}
//...
}
?>
I couldn't find much info on stacking the new ternary operator, so I ran some tests:
<?php
echo 0 ?: 1 ?: 2 ?: 3; //1
echo 1 ?: 0 ?: 3 ?: 2; //1
echo 2 ?: 1 ?: 0 ?: 3; //2
echo 3 ?: 2 ?: 1 ?: 0; //3
echo 0 ?: 1 ?: 2 ?: 3; //1
echo 0 ?: 0 ?: 2 ?: 3; //2
echo 0 ?: 0 ?: 0 ?: 3; //3
?>
It works just as expected, returning the first non-false value within a group of expressions.
When it comes to formatting structure of the conditional statements, I found this to work best and retain logic in views...
<?php
$z = 2;
$text = ($z===1 ? 'ONE'
: ($z===2 ? 'TWO'
: ($z===3 ? 'THREE'
: 'MORE' )));
echo($text); // RESULT='TWO'
// LONGHAND
$z = 2;
$text = ($z===1?'ONE' : ($z===2?'TWO' : ($z===3?'THREE' : 'MORE')));
echo($text); // RESULT='TWO'
?>
Since this is expected to test logic, and nothing more, only use it to test logic.
To test order, if you ever forget...
<?php
$z = 1;
$text = ($z===1 ? 'FIRST : OUTTER'
: ($z===1 ? 'SECOND : INNER'
: ($z===1 ? 'THIRD : LAST'
: 'FAIL EVAL DEFAULT' )));
echo($text); // RETURN='FIRST : OUTTER'
$z = 2;
$text = ($z===1 ? 'FIRST : OUTTER'
: ($z===1 ? 'SECOND : INNER'
: ($z===1 ? 'THIRD : LAST'
: 'FAIL EVAL DEFAULT' )));
echo($text); // RETURN='FAIL EVAL DEFAULT'
?>
(IF ? THEN : ELSE)
(IF ? THEN : ELSE(IF ? THEN : ELSE(IF ? THEN : ELSE))
That can't be read from inside to out, unlike a math formula, because the logic in comparison is not the same. In math nesting, you need the solution to the deepest nested element first. In logic comparison, you always start outside before you compare inside. (Logically, IF there is no door THEN you need something ELSE to get inside. Oh, there is a window... We are inside, now IF there is a fridge THEN open it or ELSE you starve.)
A quick way to do mysql bit comparison in php is to use the special character it stores . e.g
<?php
if ($AvailableRequests['OngoingService'] == '')
echo '<td>Yes</td>';
else
echo '<td>No</td>';
?>
"Array with fewer members is smaller, if key from operand 1 is not found in operand 2 then arrays are uncomparable, otherwise - compare value by value (see following example)."
The example covers this behaviour, but it isn't immediately obvious, so:
If you're doing loose comparisons in PHP, note that they differ from checking each value individually like $value1==$value2 by adding what amounts to an empty($value1)==empty($value2) check into the mix. I found this out by investigating some (to me) bizarre behaviour.
[Note that the example contains no ==, just > and <. It's its absence that perceivedly 'causes empty() to fire'.]
I was also pleasantly surprised to see PHP recurse. Also clear if you keep in mind that the example implies another function call to itself with > and < if both operands are arrays, but IMO definitely worth stating.
It might also be worth noting that the order of array keys doesn't matter, even if a foreach() would see a 'different' array. Again, covered by the example, but might be worth stressing.
Note: The ternary shortcut currently seems to be of no use in dealing with unexisting keys in an array, as PHP will throw an error. Take the following example.
<?php
$_POST['Unexisting'] = $_POST['Unexisting'] ?: false;
?>
PHP will throw an error that the "Unexisting" key does not exist. The @ operator does not work here to suppress this error.
U can even add a variable on that if u wish:
($Profile['skinstyle']=='0')? $lol = "selected":"";
then call it out.. alot faster. if u use EOF.. and such like on ibp :(
Here is some ternary trick I like to use for selecting a default value in a set of radio buttons. This example assumes that a prior value was known and that we are offering a user the chance to edit that prior value. If no prior value was actually known, no default value will be set.
<form>
<input type='radio' name='gender' value='m' <?=($gender=='m')?"checked":""?>>Male
<input type='radio' name='gender' value='f' <?=($gender=='f')?"checked":""?>>Female
</form>
When a "=" directly follows a "<?" (no space allowed in between -- the trick does not work with "<?php"), the right side of the operand (here, the result of the ternary operation) is printed out as text into the surrounding HTML code. If using "<?php" form, you will need to do "<?php echo exp1?exp2:exp3 ?>" instead.
Note that an expression where a boolean variable and a string are compared with the equal operator, will always come out true as a string is technically true. For example:
<?php
$variable = true;
if ($variable == "something") {
//This code will be excecuted
}
?>
To get around this use the identical operator ===, as the types are not the same.
The cast from null to boolean is documented (on the page describing the boolean type: null->false), and so is the cast from boolean to integer (on the page describing the integer type: false->0), but the cast from null to integer is undefined and the fact that it is currently implemented by casting from null to boolean and then from boolean to integer is explicitly documented (on the page describing the integer type) as something that should not be relied on (so null==0 is true only by accident, but ((int)(bool)null)==0 is true per specification).
Perhaps as well as a "Converting to integer" section on the integer type page there should also be a "Converting from integer" section; similarly for the other types.
Hi all:
I found this and maybe it can help you, i didn't found it documented anywhere :
Assuming you have a function that returns an array or a null value in failure and you do something like this
<?php
function myfunction()
{
if($something==$other)
{
return array(0=>array(0=>array('valor'=>$other)));
}else{
return null;
}
}
$x = myfunction();
var_dump($x); //can be null
if($x[0][0]['value'] < 1)
{
echo "nok";
}else{
echo "ok";
}
?>
If the function returns null then you get "nok" printed.
As far as I see NULL values are always less than 1, and the fact that I request a sub array ([0][0]['value']) doesn't give me any notice nor warning.
Hope this helps anybody.
Greetings
Most of the time, you may be content with your conditionals evaluating to true if they are evaluating a non-false, non-zero value. You may also like it when they evaluate to false when you use the number 0.
However, there may be times where you want to make a distinction between a non-false value and a boolean true. You may also wish to make a distinction between a boolean false and a zero.
The identity operator can make this distinction for you.
<?php
$a = 'some string';
$b = 123;
$c = 0;
if($a && $b && (!$c))
{ echo "True.\n"; } else { echo "False.\n"; }
if($a == true && $b == true && $c == false)
{ echo "True.\n"; } else { echo "False.\n"; }
if($a === true || $b === true || $c === false)
{ echo "True.\n"; } else { echo "False.\n"; }
?>
The above code outputs the following:
True.
True.
False.
As you can see, in the first two cases, $a and $b are considered true, while $c is considered false. If this wasn't the case, neither of the first two conditionals would have echoed "True."
In the last case, I've cleverly used the || operator to demonstrate that both $a and $b do not evaluate to true with the identity operator, nor does $c evaluate to false.
The === operator can be used to distinguish boolean from non-boolean values.
This seems a bit odd to me, but PHP can convert two strings into integers during comparison. For example: "700" == "+700" return true even though they are totally different strings.
Use === or strcmp when comparing two strings to ensure that they remain as strings during comparison.
Note that the "ternary operator" is better described as the "conditional operator". The former name merely notes that it has three arguments without saying anything about what it does. Needless to say, if PHP picked up any more ternary operators, this will be a problem.
"Conditional Operator" is actually descriptive of the semantics, and is the name historically given to it in, e.g., C.
Be careful when using the ternary operator!
The following will not evaluate to the expected result:
<?php
echo "a string that has a " . (true) ? 'true' : 'false' . " condition in. ";
?>
Will print true.
Instead, use this:
<?php
echo "a string that has a " . ((true) ? 'true' : 'false') . " condition in. ";
?>
This will evaluate to the expected result: "a string that has a true condition in. "
I hope this helps.
If you need nested ifs on I var its important to group the if so it works.
Example:
<?php
//Dont Works
//Parse error: parse error, unexpected ':'
$var='<option value="1" '.$status == "1" ? 'selected="selected"' :''.'>Value 1</option>';
//Works:
$var='<option value="1" '.($status == "1" ? 'selected="selected"' :'').'>Value 1</option>';
echo $var;
?>
Note that typecasting will NOT prevent the default behavior for converting two numeric strings to numbers when comparing them.
e.g.:
<?php
if ((string) '0123' == (string) '123')
print 'equals';
else
print 'doesn\'t equal';
?>
Still prints 'equals'
As far as I can tell the only way to avoid this is to use the identity comparison operators (=== and !==).
Since php 5.2 the operator == for object vs object is not recursion safe, it will cause a fatal error if one of the objects contains a refernce to it self (indirect refferences also counts here).
If you are just checking if two object pointers points to the same object use === instead and aviod this issue (you might get a minimal speed bost too).
When you want to know if two arrays contain the same values, regardless of the values' order, you cannot use "==" or "===". In other words:
<?php
(array(1,2) == array(2,1)) === false;
?>
To answer that question, use:
<?php
function array_equal($a, $b) {
return (is_array($a) && is_array($b) && array_diff($a, $b) === array_diff($b, $a));
}
?>
A related, but more strict problem, is if you need to ensure that two arrays contain the same key=>value pairs, regardless of the order of the pairs. In that case, use:
<?php
function array_identical($a, $b) {
return (is_array($a) && is_array($b) && array_diff_assoc($a, $b) === array_diff_assoc($b, $a));
}
?>
Example:
<?php
$a = array (2, 1);
$b = array (1, 2);
// true === array_equal($a, $b);
// false === array_identical($a, $b);
$a = array ('a' => 2, 'b' => 1);
$b = array ('b' => 1, 'a' => 2);
// true === array_identical($a, $b)
// true === array_equal($a, $b)
?>
(See also the solution "rshawiii at yahoo dot com" posted)
You should be very careful when using == with an result set returned from a query that can be an empty array, multi-dimensional array or a boolean false value (if the query failed to execute). In PHP, an empty array is equivalent to true.
<?php
$myArray = array();
// check if there is any error with the query
if ($myArray == false)
{
echo "Yes";
}
?>
return Yes
Use === instead.
I think everybody should read carefully what "jeronimo at DELETE_THIS dot transartmedia dot com" wrote. It's a great pitfall even for seasoned programmers and should be looked upon with a great attention.
For example, comparing passwords with == may result in a very large security hole.
I would add some more to it:
The workaround is to use strcmp() or ===.
Note on ===:
While the php documentation says that, basically,
($a===$b) is the same as ($a==$b && gettype($a) == gettype($b)),
this is not true.
The difference between == and === is that === never does any type conversion. So, while, according to documentation, ("+0.1" === ".1") should return true (because both are strings and == returns true), === actually returns false (which is good).
Note: according to the spec, PHP's comparison operators are not transitive. For example, the following are all true in PHP5:
"11" < "a" < 2 < "11"
As a result, the outcome of sorting an array depends on the order the elements appear in the pre-sort array. The following code will dump out two arrays with *different* orderings:
<?php
$a = array(2, "a", "11", 2);
$b = array(2, "11", "a", 2);
sort($a);
var_dump($a);
sort($b);
var_dump($b);
?>
This is not a bug report -- given the spec on this documentation page, what PHP does is "correct". But that may not be what was intended...
You can't just compare two arrays with the === operator
like you would think to find out if they are equal or not. This is more complicated when you have multi-dimensional arrays. Here is a recursive comparison function.
<?php
/**
* Compares two arrays to see if they contain the same values. Returns TRUE or FALSE.
* usefull for determining if a record or block of data was modified (perhaps by user input)
* prior to setting a "date_last_updated" or skipping updating the db in the case of no change.
*
* @param array $a1
* @param array $a2
* @return boolean
*/
function array_compare_recursive($a1, $a2)
{
if (!(is_array($a1) and (is_array($a2)))) { return FALSE;}
if (!count($a1) == count($a2))
{
return FALSE; // arrays don't have same number of entries
}
foreach ($a1 as $key => $val)
{
if (!array_key_exists($key, $a2))
{return FALSE; // uncomparable array keys don't match
}
elseif (is_array($val) and is_array($a2[$key])) // if both entries are arrays then compare recursive
{if (!array_compare_recursive($val,$a2[$key])) return FALSE;
}
elseif (!($val === $a2[$key])) // compare entries must be of same type.
{return FALSE;
}
}
return TRUE; // $a1 === $a2
}
?>
Don't be deceived into thinking that === compares objects for identity, it does not. It does a recusrive comparison which fails if there are recusrive object references involved, and will report as identical two different object instances that happen to merely have the same value.
You can see the stated problem at: http://bugs.php.net/bug.php?id=35053
My workaround is php::CompareObjects($a,$b)
<?php
# static class to hold methods to encapsulate php deficiencies in various versions
class php {
# in === on objects in php4 does a dumb recusrive check instead
function CompareObject(&$a,&$b) {
$value='Bah! Stupid===';
$key="bah".rand(0,1000);
while(isset($a->$key)) $key.=rand(0,9);
if (isset($b->$key)) return FALSE;
$a->$key=$value;
$result=($a->$key===$b->$key);
unset($a->$key);
return $result;
}
}
?>
The following contrasts the trinary operator associativity in PHP and Java. The first test would work as expected in Java (evaluates left-to-right, associates right-to-left, like if stmnt), the second in PHP (evaluates and associates left-to-right)
<?php
echo "\n\n######----------- trinary operator associativity\n\n";
function trinaryTest($foo){
$bar = $foo > 20
? "greater than 20"
: $foo > 10
? "greater than 10"
: $foo > 5
? "greater than 5"
: "not worthy of consideration";
echo $foo." => ".$bar."\n";
}
echo "----trinaryTest\n\n";
trinaryTest(21);
trinaryTest(11);
trinaryTest(6);
trinaryTest(4);
function trinaryTestParens($foo){
$bar = $foo > 20
? "greater than 20"
: ($foo > 10
? "greater than 10"
: ($foo > 5
? "greater than 5"
: "not worthy of consideration"));
echo $foo." => ".$bar."\n";
}
echo "----trinaryTestParens\n\n";
trinaryTestParens(21);
trinaryTestParens(11);
trinaryTest(6);
trinaryTestParens(4);
?>
Output:
######----------- trinary operator associativity
----trinaryTest
21 => greater than 5
11 => greater than 5
6 => greater than 5
4 => not worthy of consideration
----trinaryTestParens
21 => greater than 20
11 => greater than 10
6 => greater than 5
4 => not worthy of consideration
Hi folks,
to the float comparison problem...
This worked for me:
<?php
//! compare two floating point values, return true if they are equal
//! (enough) or false otherwise
function float_equal($f1, $f2)
{
return ($f1 > $f2) ? (false) : (!($f1 < $f2));
}
// compare floats
$f1 = 0.037;
$f2 = 1000387.978;
echo "$f1 and $f2 are ".(float_equal($f1,$f2)?("equal"):("not equal"))."<br />";
$f1 = 0.3;
$f2 = 0.3;
echo "$f1 and $f2 are ".(float_equal($f1,$f2)?("equal"):("not equal"))."<br />";
?>
Concerning floats: It is simply pointless to compare a float with the value "0.3". The number 0.3 is not exactly representable in binary. Period. So is the number 0.1, and an infinite number of others numbers. Just like 1/3 is not exactly representable in decimal. How would you code the test for your float to be one third? Maybe $myFloat == 0.33333333333 Hmm: you see: Everyone would agree that this test is not accurate.
The test $myFloat == 0.3 is making exactly the same mistake.
So the float which you think should be 0.3 is really something very close to it; if you print it in decimal, the conversion will end up with the closest decimal representation, which may well be "0.3". But "0.3" is also the "right display decimal" for hundreds of float values.
The correct way to "compare" floats is: ( $myFloat - 0.3 ) < $EPSILON where $EPSILON is something like 1e-10, depending on your application. Approximate algorithms are the only right way to treat floats, which are only approximate by themselves.
be REALLY careful when comparing float values. PHP, like most languages, is vunerable to he problems of floating point precision.
Do NOT compare floats directly, and this also means any decimal value at all.
The headaches finding out if $var = 0.3 caused me are unbelievable. even though the stored variable WAS 0.3 it was still ignoring it - this was to do with the internal float not recognising it as 0.3 even though it *displayed* it as 0.3 when echo'd or printed... basically it was stored imprecisly, but not able to display it as such.
I ended up having to compare after multiplying by 10, rounding, and then dividing by 10... rediculous, but sadly the only way I could find to reliably do it. The round seemed to remove the break in the float...
jesus that took me ages to find...
if you want to use the ?: operator, you should be careful with the precedence.
Here's an example of the priority of operators:
<?php
echo 'Hello, ' . isset($i) ? 'my friend: ' . $username . ', how are you doing?' : 'my guest, ' . $guestusername . ', please register';
?>
This make "'Hello, ' . isset($i)" the sentence to evaluate. So, if you think to mix more sentences with the ?: operator, please use always parentheses to force the proper evaluation of the sentence.
<?php
echo 'Hello, ' . (isset($i) ? 'my friend: ' . $username . ', how are you doing?' : 'my guest, ' . $guestusername . ', please register');
?>
for general rule, if you mix ?: with other sentences, always close it with parentheses.
For converted Perl programmers: use strict comparison operators (===, !==) in place of string comparison operators (eq, ne). Don't use the simple equality operators (==, !=), because ($a == $b) will return TRUE in many situations where ($a eq $b) would return FALSE.
For instance...
"mary" == "fred" is FALSE, but
"+010" == "10.0" is TRUE (!)
In the following examples, none of the strings being compared are identical, but because PHP *can* evaluate them as numbers, it does so, and therefore finds them equal...
<?php
echo ("007" == "7" ? "EQUAL" : "not equal");
// Prints: EQUAL
// Surrounding the strings with single quotes (') instead of double
// quotes (") to ensure the contents aren't evaluated, and forcing
// string types has no effect.
echo ( (string)'0001' == (string)'+1.' ? "EQUAL" : "not equal");
// Prints: EQUAL
// Including non-digit characters (like leading spaces, "e", the plus
// or minus sign, period, ...) can still result in this behavior, if
// a string happens to be valid scientific notation.
echo (' 131e-2' == '001.3100' ? "EQUAL" : "not equal");
// Prints: EQUAL
?>
If you're comparing passwords (or anything else for which "near" precision isn't good enough) this confusion could be detrimental. Stick with strict comparisons...
<?php
// Same examples as above, using === instead of ==
echo ("007" === "7" ? "EQUAL" : "not equal");
// Prints: not equal
echo ( (string)'0001' === (string)'+1.' ? "EQUAL" : "not equal");
// Prints: not equal
echo (' 131e-2' === '001.3100' ? "EQUAL" : "not equal");
// Prints: not equal
?>
WARNING!!!!
Let's say, we have this little script:
<?php
$username = 'Me';
$guestusername = 'Guest';
echo 'Hello, ' . isset($i) ? 'my friend: ' . $username . ', how are you doing?' : 'my guest, ' . $guestusername . ', please register';
?>
What you want:
If $i is set, display:
Hello, my friend: Me, how are you doing?
If not, display:
Hello, my guest, Guest, please register
BUT, you DON'T get that result!
If $i is set, you get this:
my friend: Me, how are you doing? (so, there's not "Hello, " before it)
If $i is NOT set, you get this:
my friend: Me, how are you doing?
So... That's the same!
You can solve this by using the "(" and ")" to give priority to the ternary operator:
<?php
$username = 'Me';
$guestusername = 'Guest';
echo 'Hello, ' . (isset($i) ? 'my friend: ' . $username . ', how are you doing?' : 'my guest, ' . $guestusername . ', please register');
?>
When $i is set, you get this:
Hello, my friend: Me, how are you doing? (expected)
When $i is NOT set, you get this:
Hello, my guest, Guest, please register (expected too)
So.. Please, don't be dumb and ALWAYS use the priority-signs (or.. How do you call them?), ( and ).
By using them, you won't get unneeded trouble and always know for sure your code is doing what you want: The right thing.
With Nested ternary Operators you have to set the logical parentheses to get the correct result.
<?php
$test=true;
$test2=true;
($test) ? "TEST1 true" : ($test2) ? "TEST2 true" : "false";
?>
This will output: TEST2 true;
correct:
<?php
$test=true;
$test2=true;
($test) ? "TEST1 true" : (($test2) ? "TEST2 true" : "false");
?>
Anyway don't nest them to much....!!
note: the behavior below is documented in the appendix K about type comparisons, but since it is somewhat buried i thought i should raise it here for people since it threw me for a loop until i figured it out completely.
just to clarify a tricky point about the == comparison operator when dealing with strings and numbers:
('some string' == 0) returns TRUE
however, ('123' == 0) returns FALSE
also note that ((int) 'some string') returns 0
and ((int) '123') returns 123
the behavior makes senes but you must be careful when comparing strings to numbers, e.g. when you're comparing a request variable which you expect to be numeric. its easy to fall into the trap of:
if ($_GET['myvar']==0) dosomething();
as this will dosomething() even when $_GET['myvar'] is 'some string' and clearly not the value 0
i was getting lazy with my types since php vars are so flexible, so be warned to pay attention to the details...
Diese Seite bei php.net