布尔型

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

注意: 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。


// == is an operator which test
// equality and returns a boolean
if ($action == "show_version") {
    echo "The version is 1.23";
}

// this is not necessary...
if ($show_separators == TRUE) {
    echo "<hr>\n";
}

// ...because you can simply type
if ($show_separators) {
    echo "<hr>\n";
}

转换为布尔值

要明示地将一个值转换成 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：

布尔值 FALSE
整型值 0（零）
浮点型值 0.0（零）
空白字符串和字符串 "0"
没有成员变量的数组
没有单元的对象（仅适用于 PHP 4）
特殊类型 NULL（包括尚未设定的变量）

所有其它值都被认为是 TRUE（包括任何资源）。

警告

-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)
?>

add a note User Contributed Notes

openspecies
13-Jul-2007 03:22


function is_odd($x) { return ($x & 1); //integer }

function is_even($x) { return (!($x & 1)); //integer }



if(is_even(10) === TRUE) 

  // NO



function is_odd($x) { return (bool) ($x & 1); //boolean }

function is_even($x) { return  (bool) (!($x & 1)); //boolean }



if(is_even(10) === TRUE) 

  // YES



$str = 'Hello World!';



if($str === TRUE) 

  // ecetera



@+

Schraalhans Keukenmeester
23-May-2007 05:03


Re: andy at txtnation dot com

<quote> The braces are of course optional </quote>



Nothing optional about the 'braces'  here.

'(  )' are parentheses. '{  }' are braces. But we get the point.



<?php

$num = 10;

$isEven = !($num % 2);

echo ($isEven) ? 'Even' : 'Odd';

//outputs : Even

$isEven = !$num % 2;

echo ($isEven) ? 'Even' : 'Odd';

//outputs : Odd (with ANY number != 0 !!)

?>



Operator precedence and implicit casts at work:

$num = 10;

!$num       => (implicit cast to bool) $num: (bool) 10 = true

!true       => negate true : false

false % 2   => (implicit cast to int) false : (int) false = 0

0 % 2       => remainder of 0 intdiv 2 : 0

$isEven = 0 => integer assignment : 0

($isEven) ? => (implicit cast to bool) 0 : (bool) 0 = false

echo (false) ? 'Even' : 'Odd' => condition false : 'Odd'



Wether or not PHP actually performs the (bool) casts under the hood is irrelevant to the outcome here.

terminatorul at gmail dot com
29-Apr-2007 09:21


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.

12-Mar-2007 03:45


Jasper probably meant:

$a = 2; 

$b = 3; 

$aBiggerThanB = $a > $b;

andy at txtnation dot com
25-Feb-2007 05:31


Re: comment from jasper at jtey dot com



It is better to not explicitly test for default values. PHP knows the default values, and so should any programmer worth her/his salt.



Same example rewritten:



<?php

$num = 10;

$isEven = !($num % 2);

?>



The braces are off course optional.

jasper at jtey dot com
05-Jun-2006 07:51


The following expressions are equivalent:


<?php


// setting true


$flag = true;


$flag = True;


$flag = TRUE;


$flag = 1==1;





// setting false


$flag = false;


$flag = False;


$flag = FALSE;


$flag = 1==2;


?>





The moral of the story is that boolean operators return a boolean value, i.e., "1==1" returns a boolean value of true.  Someone who is not aware of this may write a block of code such as:


<?php


// even number?


$num = 10;


if($num % 2 == 0){


  $isEven = true;


}


else{


  $isEven = false;


}


?>





when all that is needed is:


<?php


$num = 10;


$isEven = $num % 2 == 0;


?>





Other examples, for illustrative purposes:


<?php


// two numbers


$a = 2;


$b = 3;


$aBiggerThanB = 2 > 3; // $aBiggerThanB is set to false





// lower case vowel check (corrected)


$c = "u";


$isVowel = $c == "a"|| $c == "e"|| $c == "i"|| $c == "o"|| $c == "u";


?>

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