类型
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PHP手册

布尔类型

这是最简单的类型。boolean 表达了真值，可以为 TRUE 或 FALSE。

Note: 布尔类型是 PHP 4 引进的。

语法

要指定一个布尔值，使用关键字 TRUE 或 FALSE。两个都不区分大小写。

<?php
$foo = True; // assign the value TRUE to $foo
?>

通常你用某些运算符返回 boolean 值，并将其传递给控制流程。

<?php
// == 是一个操作符，它检测两个变量是否相等，并返回一个布尔值
if ($action == "show_version") {
    echo "The version is 1.23";
}

// 这样做是不必要的...
if ($show_separators == TRUE) {
    echo "<hr>\n";
}

// ...因为可以使用下面这种简单的方式：
if ($show_separators) {
    echo "<hr>\n";
}
?>

转换为布尔值

要明确地将一个值转换成 boolean，用 (bool) 或者 (boolean) 来强制转换。但是很多情况下不需要用强制转换，因为当运算符，函数或者流程控制结构需要一个 boolean 参数时，该值会被自动转换。

参见类型戏法。

当转换为 boolean 时，以下值被认为是 FALSE：

所有其它值都被认为是 TRUE（包括任何资源）。

Warning

-1 和其它非零值（不论正负）一样，被认为是 TRUE！

<?php
var_dump((bool) "");        // bool(false)
var_dump((bool) 1);         // bool(true)
var_dump((bool) -2);        // bool(true)
var_dump((bool) "foo");     // bool(true)
var_dump((bool) 2.3e5);     // bool(true)
var_dump((bool) array(12)); // bool(true)
var_dump((bool) array());   // bool(false)
var_dump((bool) "false");   // bool(true)
?>
类型
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PHP手册
PHP手册 - N: 布尔类型

用户评论:

pablo at loop-sistemas dot com dot ar (09-Aug-2011 08:22)

altough it may be obvious to some, special value NaN evaluates to true, as it not in the false list

the same goes with INF and -INF

frank at interactinet dot com (02-May-2011 06:15)

Be careful when assigning a value in the if statement, for example:

 if($var = $arg)

$var might be assigned "1" instead of the expected value in $arg.

<?php

public function myMethod()
{
return 'test';
}

public function myOtherMethod()
{
return null;
}

if($val = $this->myMethod())
{
 // $val might be 1 instead of the expected 'test'
}

if( ($val = $this->myMethod()) )
{
// now $val should be 'test'
}

// or to check for false
if( !($val = $this->myMethod()) )
{
// this will not run since $val = 'test' and equates to true
}

// this is an easy way to assign default value only if a value is not returned:

if( !($val = $this->myOtherMethod()) )
{
$val = 'default'
}

?>

oscar at oveas dot com (01-Dec-2010 11:17)

Dunno if someone else posted this solution already, but if not, here's a useful and function to convert strings to strict booleans.
Note this one only checks for string and defaults to the PHP (boolean) cast where e.g. -1 returns true, but you easily add some elseifs for other datatypes.

<?php
function toStrictBoolean ($_val, $_trueValues = array('yes', 'y', 'true'), $_forceLowercase = true)
{
    if (is_string($_val)) {
        return (in_array(
             ($_forceLowercase?strtolower($_val):$_val)
            , $_trueValues)
        );
    } else {
        return (boolean) $_val;
    }
}
?>

ledadu at gmail dot com (27-Oct-2010 04:56)

Function to sort array by elements and count of element (before php 5.3) (not use Lambda Functions, and Closures)

<?php

//-----------------------------

function arraySortByElements($array2sort,$sortField,$order,$iscount=false) {
    
        $functionString='
        if ('.($iscount?'true':'false').'){
              if(count($a["'.$sortField.'"]) > count($b["'.$sortField.'"])) return 1*'.$order.';
            if(count($a["'.$sortField.'"]) < count($b["'.$sortField.'"])) return -1*'.$order.';
          }else{
            if($a["'.$sortField.'"] > $b["'.$sortField.'"]) return 1*'.$order.';
            if($a["'.$sortField.'"] < $b["'.$sortField.'"]) return -1*'.$order.';
          }
        return 0;';
       
     usort($array2sort, create_function('$a,$b',$functionString));
     return $array2sort;
}

//-----------------------------

//init Array for testing :
$testArray = array(
          array('name' => 'Lenny', 'note' => 5, 'listId' => array(654,987,32165)),
          array('name' => 'Olivier', 'note' =>3, 'listId' => array(2)),
          array('name' => 'Gregory', 'note' => 1, 'listId' => array(45,58)),
          array('name' => 'Clement', 'note' => 2, 'listId' => array(584,587,741,14781,147))
        );

//sorted Arrays :
        $testArrayByNameASC = arraySortByElements($testArray,'name',1);
        $testArrayByNoteDESC = arraySortByElements($testArray,'note',-1);
        $testArrayByCountlistIdDESC = arraySortByElements($testArray,'listId',-1,true);

?>

mobil dot boty at no dot spam dot gmail dot com (08-Jul-2010 10:33)

<?php
function test() {
     return TRUE;
}

$var = test();

// FASE instead of FALSE

if ($var == FASE) {
     echo 'function returned FALSE';
} else {
     echo 'function returned TRUE';
}

// will output : function returned FALSE
?>

   Just spent 10 mins trying to figure out why a function returned false when it didn't, so check your typing or use === instead of ==

fyrye at torntech dot com (14-Jun-2010 12:39)

Since I haven't seen it posted.
Here is a function that you can use if you have a need to force strict boolean values.
Hopefully this will save someone some time from searching for similar.
<?php
function strictBool($val=false){
    return is_integer($val)?false:$val == 1;
}
?>

Simply put, it verifies that the value passed is (bool)true otherwise it's false.

Examples:
__________________________________
<?php
$myBool = strictBool(true);
var_dump($myBool);
//returns (bool)true

$myar = array(0 => true);
$myBool = strictBool($myar[0]);
var_dump($myBool);
//returns (bool)true

$myBool = strictBool("hello");
var_dump($myBool);
//returns (bool)false

$myBool = strictBool(false);
var_dump($myBool);
//returns (bool)false

$myBool = strictBool(array(0 => "hello"));
var_dump($myBool);
//returns (bool)false

$myBool = strictBool(1);
var_dump($myBool);
//returns (bool)false

$myBool = strictBool();
var_dump($myBool);
//returns (bool)false
?>

mercusmaximus at yahoo dot com (06-Feb-2010 09:50)

Note that the comparison: (false == 0) evaluates to true and so will any value you set to false as well (without casting).

Symbol (11-Apr-2009 09:35)

Just a side note, doesn't really matters, the reason -1 is true and not false is because boolean type is treated as unsigned, so -1 would be for example, if it's unsigned int32 translate to hex: 0xFFFFFFFF and back to decimal: 4294967295 which is non-zero. there isn't really a "negative boolean". it's a binary thing. :o (since it used to be a bit and then there was only 0 and 1 as an option)

russell dot harper at springboardnetworks dot com (02-Apr-2009 02:27)

PHP is very fussy converting strings to booleans. The only ones it recognizes are '0' or '', everything else evaluates to TRUE, even 'false' and '0.0' are evaluated as true! I suppose this can't be fixed without breaking a lot of existing code.

Example:

<?php

print 'yes'."\t".((bool)'yes'? 1: 0)."\n";
print 'true'."\t".((bool)'true'? 1: 0)."\n";
print 'no'."\t".((bool)'no'? 1: 0)."\n";
print 'false'."\t".((bool)'false'? 1: 0)."\n";
print '1'."\t".((bool)'1'? 1: 0)."\n";
print '0'."\t".((bool)'0'? 1: 0)."\n";
print '0.0'."\t".((bool)'0.0'? 1: 0)."\n";
print ''."\t".((bool)''? 1: 0)."\n";

?>

Output:

yes     1
true    1
no      1
false   1
1       1
0       0
0.0     1
        0

ashafer01 at gmail dot com (26-Feb-2009 03:59)

A note when working with PostgreSQL - if you select a boolean field from the database, it returns 't' or 'f'. If you directly evaluate a variable storing a boolean from a PostgreSQL database, it will always return true.

For example...

<?php
$x = pg_query("SELECT someBool FROM atable");
$x = pg_fetch_array($x);
$x = $x['someBool'];

if ($x) echo "true";
else echo "false";
?>

...ALWAYS outputs true

admin at eexit dot fr (04-Nov-2008 08:27)

Beware of certain control behavior with boolean and non boolean values :

<?php
// Consider that the 0 could by any parameters including itself
var_dump(0 == 1); // false
var_dump(0 == (bool)'all'); // false
var_dump(0 == 'all'); // TRUE, take care
var_dump(0 === 'all'); // false

// To avoid this behavior, you need to cast your parameter as string like that :
var_dump((string)0 == 'all'); // false
?>

wbcarts at juno dot com (06-Oct-2008 07:59)

CODING PRACTICE...

Much of the confusion about booleans (but not limited to booleans) is the fact that PHP itself automatically makes a type cast or conversion for you, which may NOT be what you want or expect. In most cases, it's better to provide functions that give your program the exact behavior you want.
<?php

function boolNumber($bValue = false) {                      // returns integer
  return ($bValue ? 1 : 0);
}

function boolString($bValue = false) {                      // returns string
  return ($bValue ? 'true' : 'false');
}

$a = true;                                                  // boolean value
echo 'boolean $a AS string = ' . boolString($a) . '<br>';   // boolean as a string
echo 'boolean $a AS number = ' . boolNumber($a) . '<br>';   // boolean as a number
echo '<br>';

$b = (45 > 90);                                             // boolean value
echo 'boolean $b AS string = ' . boolString($b) . '<br>';   // boolean as a string
echo 'boolean $b AS number = ' . boolNumber($b) . '<br>';   // boolean as a number
echo '<br>';

$c = boolNumber(10 > 8) + boolNumber(!(5 > 10));            // adding booleans
echo 'integer $c = ' . $c .'<br>';

?>
Results in the following being printed...

 boolean $a AS string = true
 boolean $a AS number = 1

 boolean $b AS string = false
 boolean $b AS number = 0

 integer $c = 2

In other words, if we know what we want out of our program, we can create functions to accommodate. Here, we just wanted 'manual control' over numbers and strings, so that PHP doesn't confuse us.

Wackzingo (27-Jan-2008 02:39)

It is correct that TRUE or FALSE should not be used as constants for the numbers 0 and 1. But there may be times when it might be helpful to see the value of the Boolean as a 1 or 0. Here's how to do it.

<?php
$var1 = TRUE;
$var2 = FALSE;

echo $var1; // Will display the number 1

echo $var2; //Will display nothing

/* To get it to display the number 0 for
a false value you have to typecast it: */

echo (int)$var2; //This will display the number 0 for false.
?>

Steve (15-Jan-2008 11:00)

PHP does not break any rules with the values of true and false.  The value false is not a constant for the number 0, it is a boolean value that indicates false.  The value true is also not a constant for 1, it is a special boolean value that indicates true.  It just happens to cast to integer 1 when you print it or use it in an expression, but it's not the same as a constant for the integer value 1 and you shouldn't use it as one.  Notice what it says at the top of the page:

A boolean expresses a truth value.

It does not say "a boolean expresses a 0 or 1".

It's true that symbolic constants are specifically designed to always and only reference their constant value.  But booleans are not symbolic constants, they are values.  If you're trying to add 2 boolean values you might have other problems in your application.

Anonymous (06-Jan-2008 03:05)

Note that the symbolic constants TRUE and FALSE are treated differently.  I was told that this is a feature, not a bug.

echo false ;
echo (false) ;
echo false+false ;
echo (false+false) ;
echo intval(false) ;
echo '"'.false.'"' ;

echo true ;
echo (true) ;
echo true+true ;
echo (true+true) ;
echo intval(true) ;
echo '"'.true.'"' ;

should produce

00000"0"11221"1"

but instead produces

000""11221"1"

In other words, the only way to output the underlying zero or use it in a string is to use 'false+false' or pass it through intval().  No such tricks are required to get at the 1 that underlies true.

The whole idea of symbolic constants is that the underlying value *always* replaces them during translation, and thus anywhere you would otherwise have to use some obscure "magic number" such as 191, you can use a symbolic constant that makes sense, such as TOTAL_NATIONS. 

Exactly what php gets out of breaking this rule was not explained to me.

artktec at gmail dot com (27-Sep-2007 05:37)

Note you can also use the '!' to convert a number to a boolean, as if it was an explicit (bool) cast then NOT.

So you can do something like:

<?php
$t = !0; // This will === true;
$f = !1; // This will === false;
?>

And non-integers are casted as if to bool, then NOT.

Example:

<?php
$a = !array();      // This will === true;
$a = !array('a');   // This will === false;
$s = !"";           // This will === true;
$s = !"hello";      // This will === false;
?>

To cast as if using a (bool) you can NOT the NOT with "!!" (double '!'), then you are casting to the correct (bool).

Example:

<?php
$a = !!array();   // This will === false; (as expected)
/*
This can be a substitute for count($array) > 0 or !(empty($array)) to check to see if an array is empty or not  (you would use: !!$array).
*/

$status = (!!$array ? 'complete' : 'incomplete');

$s = !!"testing"; // This will === true; (as expected)
/*
Note: normal casting rules apply so a !!"0" would evaluate to an === false
*/
?>

terminatorul at gmail dot com (29-Apr-2007 10:21)

Beware that "0.00" converts to boolean TRUE !

You may get such a string from your database, if you have columns of type DECIMAL or CURRENCY. In such cases you have to explicitly check if the value is != 0 or to explicitly convert the value to int also, not only to boolean.