运算符
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比较运算符

比较运算符，如同它们名称所暗示的，允许对两个值进行比较。还可以参考 PHP 类型比较表看不同类型相互比较的例子。

比较运算符
例子 名称 结果
$a == $b 等于 TRUE，如果 $a 等于 $b。
$a === $b 全等 TRUE，如果 $a 等于 $b，并且它们的类型也相同。（PHP 4 引进）
$a != $b 不等 TRUE，如果 $a 不等于 $b。
$a <> $b 不等 TRUE，如果 $a 不等于 $b。
$a !== $b 非全等 TRUE，如果 $a 不等于 $b，或者它们的类型不同。（PHP 4 引进）
$a < $b 小与 TRUE，如果 $a 严格小于 $b。
$a > $b 大于 TRUE，如果 $a 严格 $b。
$a <= $b 小于等于 TRUE，如果 $a 小于或者等于 $b。
$a >= $b 大于等于 TRUE，如果 $a 大于或者等于 $b。

如果比较一个整数和字符串，则字符串会被转换为整数。如果比较两个数字字符串，则作为整数比较。此规则也适用于 switch 语句。

<?php
var_dump(0 == "a"); // 0 == 0 -> true
var_dump("1" == "01"); // 1 == 1 -> true
var_dump("1" == "1e0"); // 1 == 1 -> true
switch ("a") {
case 0:
    echo "0";
    break;
case "a": // never reached because "a" is already matched with 0
    echo "a";
    break;
}
?>

对于多种类型，比较运算符根据下表比较（按顺序）。

比较多种类型
运算数 1 类型 运算数 1 类型 结果
null 或 string string 将 NULL 转换为 ""，进行数字或词汇比较
bool 或 null 任何其它类型 转换为 bool，FALSE < TRUE
object object 内置类可以定义自己的比较，不同类不能比较，相同类和数组同样方式比较属性（PHP 4 中），PHP 5 有其自己的说明
string，resource 或 number string，resource 或 number 将字符串和资源转换成数字，按普通数学比较
array array 具有较少成员的数组较小，如果运算数 1 中的键不存在于运算数 2 中则数组无法比较，否则挨个值比较（见下例）
array 任何其它类型 array 总是更大
object 任何其它类型 object 总是更大

Example #1 标准数组比较代码

<?php
// 数组是用标准比较运算符这样比较的
function standard_array_compare($op1, $op2)
{
    if (count($op1) < count($op2)) {
        return -1; // $op1 < $op2
    } elseif (count($op1) > count($op2)) {
        return 1; // $op1 > $op2
    }
    foreach ($op1 as $key => $val) {
        if (!array_key_exists($key, $op2)) {
            return null; // uncomparable
        } elseif ($val < $op2[$key]) {
            return -1;
        } elseif ($val > $op2[$key]) {
            return 1;
        }
    }
    return 0; // $op1 == $op2
}
?>

参见 strcasecmp()，strcmp()，数组运算符和类型一章。

三元运算符

另一个条件运算符是“?:”（或三元）运算符 。

Example #2 赋默认值

<?php
 // Example usage for: Ternary Operator
 $action = (empty($_POST['action'])) ? 'default' : $_POST['action'];

 // The above is identical to this if/else statement
 if (empty($_POST['action'])) {
     $action = 'default';
 } else {
     $action = $_POST['action'];
 }

 ?>
表达式 (expr1) ? (expr2) : (expr3) 在 expr1 求值为 TRUE 时的值为 expr2，在 expr1 求值为 FALSE 时的值为 expr3。

Note: 注意三元运算符是个语句，因此其求值不是变量，而是语句的结果。如果想通过引用返回一个变量这点就很重要。在一个通过引用返回的函数中语句 return $var == 42 ? $a : $b; 将不起作用，以后的 PHP 版本会为此发出一条警告。

Note:

建议避免将三元运算符堆积在一起使用。当在一条语句中使用多个三元运算符时会造成 PHP 运算结果不清晰： Is is recommended that you avoid "stacking" ternary expressions. PHP's behaviour when using more than one ternary operator within a single statement is non-obvious:

Example #3 不清晰的三元运算符行为

<?php
// 乍看起来下面的输出是 'true'
echo (true?'true':false?'t':'f');

// 然而，上面语句的实际输出是't'，因为三元运算符是从左往右计算的

// 下面是与上面等价的语句，但更清晰
echo ((true ? 'true' : 'false') ? 't' : 'f');

// here, you can see that the first expression is evaluated to 'true', which
// in turn evaluates to (bool)true, thus returning the true branch of the
// second ternary expression.
?>

运算符
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PHP手册 - N: 比较运算符

用户评论:

Jeremy Swinborne (29-Mar-2012 04:06)

Beware of the consequences of comparing strings to numbers.  You can disprove the laws of the universe.

echo ('X' == 0 && 'X' == true && 0 == false) ? 'true == false' : 'sanity prevails';

This will output 'true == false'.  This stems from the use of the UNIX function strtod() to convert strings to numbers before comparing.  Since 'X' or any other string without a number in it converts to 0 when compared to a number, 0 == 0 && 'X' == true && 0 == false

lennartackermans at gmail dot com (24-Dec-2011 01:50)

Be cautious when using === and !== operators and be sure that you understand their meanings. ($a === TRUE) is not the same as ($a !== FALSE). When testing the return value of a function that may return boolean false or a value of another type (like strpos()), do not test for boolean true.

The following script will only output "Not false":

<?php

$a = 5;

if ($a === TRUE) {
    echo "True";
}  

if ($a !== FALSE) {
    echo "Not false";
}
?>

j-a-n at gmx dot de (13-Oct-2011 10:32)

Please be careful when comparing strings with floats, especally when you are using the , as decimal.

<?php
var_dump($alt);
var_dump($neu);
var_dump($alt == $neu);
?>

string(9) "590217,73"
float(590217,73)
bool(false)

not the float is cast to a string and then string-compared, but the string is cast to a float and then float-compared.

to compare as strings use strval!

<?php
var_dump(strval($alt));
var_dump(strval($neu));
var_dump(strval($alt) == strval($neu));
?>

string(9) "590217,73"
string(9) "590217,73"
bool(true)

Cuong Huy To (10-Jul-2011 03:48)

In the table "Comparison with Various Types", please move the last line about "Object" to be above the line about "Array", since Object is considered to be greater than Array (tested on 5.3.3)

(Please remove my "Anonymous" post of the same content before. You could check IP to see that I forgot to type my name)

Anonymous (10-Jul-2011 02:23)

In the table "Comparison with Various Types", please move the last line about "Object" to be above the line about "Array", since Object is considered to be greater than Array (tested on 5.3.3)

Mark Simon (16-Jun-2011 10:20)

The use of 5.3’s shortened ternary operator allows PHP to coalesce a null or empty value to an alternative:

$value = $planA ?: $planB;

My own server doesn’t yet run 5.3. A nice alternative is to use the “or” operator:

$value = $planA or $value = planB;

email at kleijn dot jp (03-May-2011 03:58)

Maybe i am overlooking something but it seems to me that using unset(string) inside a ternary operator creates an error.

(($var1==0 && $var2==0)?unset($var3):$var3=$var1+$var2);

result:
Parse error: syntax error, unexpected T_UNSET

using the traditional form of IF...ELSE works normal.

if($var1==0 && $var2==0) { unset($var3); }
else { $var3=$var1+$var2; }

result:
This unsets var3 or creates a sum of var1+var2 for var3

JP Kleijn
Netherlands

zak at minion dot net (21-Apr-2011 07:18)

be careful when trying to concatenate the result of a ternary operator to a string

<?php
print '<div>'.(FALSE) ? 'TRUE [bad ternary]' : 'FALSE [bad ternary]';
print '<br><br>';
print '<div>'.((FALSE) ? 'TRUE [good ternary]' : 'FALSE [good ternary]');
?>

yields:

TRUE [bad ternary]

FALSE [good ternary]

this is because the ternary evaluates '<div>'.(FALSE) not (FALSE) - so the end result is TRUE

me at lx dot sg (24-Sep-2010 03:08)

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 (===).

arnaud at arnapou dot net (06-Aug-2010 09:12)

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 !

mail at markuszeller dot com (04-Aug-2010 09:40)

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

michal dot kocarek at brainbox dot cz (23-May-2010 07:05)

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.

alan dot g at nospam dot net (09-May-2010 08:44)

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;
}

 

?>

taras dot bogach at gmail dot com (31-Mar-2010 03:46)

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;
    }
  }
  //...
}
?>

crazy888s at hotmail dot com (02-Feb-2010 06:32)

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.

ISAWHIM (30-Jan-2010 06:53)

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.)

kapoor_rajiv at hotmail dot com (13-Oct-2009 02:09)

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>';

?>

pinkgothic at gmail dot com (18-Sep-2009 12:28)

"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.

Anonymous (04-Aug-2009 06:44)

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.

monkuar at gmail dot com (28-Jul-2009 12:45)

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 :(

Anonymous (08-Feb-2009 02:37)

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.

mruivo at gmail dot com (21-Dec-2008 03:13)

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.

Hayley Watson (27-Oct-2008 04:45)

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.

jescribens at urbangolem dot com (04-Apr-2008 05:13)

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

Amaroq (25-Feb-2008 11:13)

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.

ken at smallboxsoftware net (15-Nov-2007 04:20)

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.

Hayley Watson (10-Apr-2007 06:38)

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.

thomas dot oldbury at tgohome dot com (27-Feb-2007 05:37)

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.

fernandoleal at dragoncs dot com (03-Feb-2007 07:19)

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;
?>

stepheneliotdewey at gmail [period] com (07-Jan-2007 02:49)

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 !==).

(04-Jan-2007 03:11)

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).

bishop (26-Oct-2006 11:49)

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)

pcdinh at phpvietnam dot net (10-Aug-2006 05:50)

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.

Alex (17-May-2006 03:49)

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).

adam at caucho dot com (09-May-2006 06:49)

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...

rshawiii at yahoo dot com (18-Jan-2006 07:36)

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
}
?>

sam at liddicott dot com (01-Nov-2005 03:42)

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;
  }
}
?>

(07-Sep-2005 09:09)

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

sven dot heyll at web dot de (05-Dec-2004 09:19)

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 />";
?>

(02-Dec-2004 11:47)

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.

darkcryst at gmail dot com (21-Oct-2004 11:35)

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...

hiroh2k at yahoo dot com (19-Oct-2004 07:05)

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.

jeronimo at DELETE_THIS dot transartmedia dot com (02-Jul-2004 12:01)

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

?>

webmaster __AT__ digitalanime __DOT__ nl (13-Apr-2004 11:31)

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.

user@example (04-Apr-2004 11:17)

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....!!

jwhiting at hampshire dot edu (09-Dec-2003 11:31)

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...