布尔型

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

注: 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

jasper at jtey dot com
08-Jun-2006 05:16


A correction to my previous note below, with regards to the following code snippet:

<?php

// lower case vowel check (incorrect)

$c = "u";

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

?>



The portion containing '$c == "a"||"e"||"i"||"o"||"u"' should be '$c == "a"|| $c == "e"|| $c == "i"|| $c == "o"|| $c == "u"' instead.  The correct code is therefore:



<?php

// lower case vowel check (corrected)

$c = "u";

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

?>

jasper at jtey dot com
06-Jun-2006 03:51


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

$c = "u";

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

?>

alex dot baldacchino at email dot it
17-May-2006 12:48


About bnab at southphlattewebdesign dot com concern, I think that's globally a casting and backward compatibility matter: as this manual states, a boolean TRUE is converted to string "1" and this is meaningful being the number 1 a - let's say - "historical" true value, while a FALSE value is converted to an empty string for some reason (I guess that may be for concatenation reason or because of an internal representation of strings with the empty string as the first/main false value and the non empty "0" string being a sort of legacy/completness secondary false value).



This is the echo behaviour with boolean types, but let's note that boolean type have been introduced in php 4, while the preg_match function was introduced previously, in php 3.0.9, so it's returned type is integer and possible results are 0 for false and 1 for true (being this a "historical", or if preferred "(ANSI) C-like" convention), so in this case the echo function is not yet converting a boolean value to a string, but a number to a string, and number convertion rules applies. In order to preserve compatibility with such a convention, a numerical value of 0 is interpreted as a boolean false in a, let's say, boolean context, as well as the string "0", so to have a correct 0 (number) -> "0" (string) -> false (boolean) -> 0 (number, again) conversion.

bnab at southphlattewebdesign dot com
11-May-2006 07:05


Assignment of a boolean value:



I beat my head on this one: Depending upon how the boolean value is assigned, it determines the actual boolean value on a FALSE value - integer, empty string etc...



Take the following example:

<?php

$x;

$i = true;

echo $i.' I should be true or 1<br><br>'; //value = 1

$i = false;

echo $i.' I should be false or 0<br><br>'; //value = ''

$i = isset($x);

echo $i.' I should be false, as X has no value<br><br>'; //value = ''

$x = 'a string';

$i = preg_match('/str/',$x);

echo $i.' I should be true on match<br><br>'; //value = 1

$i = preg_match('/trinsg/', $x);

echo $i.' I should be false on no match'; //value = 0

?>



The preg_match is false on the second time around, and thus is now assigned the boolean false value of 0.  While in trying to create a boolean literal with value false, it gets assigned as an empty string false value.  Further, I run the isset check and it assigns the empty string, while preg_match assigns the 0 value.



Maybe others grasped this simple little difference in the fact that you need to evaluate on the boolean itself, rather than the value as depending upon the assignment method, the value for FALSE can have one of several true values.

25-Jan-2006 08:00


Just a supplement to johnjc-phpdoc's post:



This 

if ( strpos($needle,$haystack) !== false )



is not the same as 

if (!strpos($needle,$haystack) === false )



for the reason he states, namely, strpos does not evaluate to true, ever.

johnjc-phpdoc at publicinfo dot net
02-Nov-2005 01:38


The === and !== are not fully documented in either the Comparison Operator or Booleans type sections. They are talked about a bit more in the sections on strpos() and array_search() but they refer you to the section on Booleans for further information. 



I am putting my contribution on === and !== in the Booleans section with pointers to it from the comment areas of other sections.



This refers only to the use of === and !== with functions like strpos() and array_search() which may a needle at character 0 in a string or element 0 in an array. Because the 0 returned by the function evaluates to == 'false' === and !== are used.  You can say 

<?php if ( strpos($needle,$haystack) !== false ) { print "found it\n"; } ?>

and you can say

<?php if ( strpos($needle,$haystack) === false ) { print "didn't find it\n"; } ?>

but you cannot say

<?php if ( strpos($needle,$haystack) === true ) { print "found it \n"; } ?>

nor can you say 

<?php if ( strpos($needle,$haystack) !== true ) { print "didn't find it\n"; } ?>



This is because strpos() and array_search do not return 'true' when successful and the numbers they return do not evaluate to === true.  So you cannot use 'true' in any way with these functions.



I frequently find myself adding string elements to an array as I find them and using the growing array as my record of what has already been done such as

<?php if ( array_search($needle,$haystack) !== false ) { print "done one of those already\n"; } ?>

or

<?php if ( array_search($needle,$haystack) === false ) { print "got a new one\n"; array_push($haystack,$needle) } ?>



The more natural way to say this would have been the other way around:

<?php if ( array_search($needle,$haystack) === true ) { print "done one of those already\n"; } ?>

or

<?php if ( array_search($needle,$haystack) !== true ) { print "got a new one\n"; array_push($haystack,$needle) } ?>

because you don't go around saying, "if this is not false", you say "if this is true".



But that won't work. Now I've had it explained to me it makes sense that the function doesn't return 'true' because it returns a number value instead. And given that === checks the type you can't have the number evaluate to '=== true'. But the result for the user of PHP is counter-intuitive and so deserves specific documenting.

x123 (at) bestof (dash) inter (dot) net
16-Nov-2004 04:24


another correction to the preceding "correction":

"as the documention states" is right,

"any non-empty string is true" is wrong : (bool) "0" === false !

(but "00" and "0.0" etc. are true!)



So watch out, you can NOT test for non-empty strings using e.g.



<?php

if (is_string($s))

  if ($s) echo " '$s' is a non-empty string";

  else echo " '$s' is an empty string"; // wrong for $s='0' !

else echo " $s is not a string ";

?>



indeed, for $s='0' this would print: " '0' is an empty string"

which is wrong, of course.

This is particularly "dangerous" in connection with MySQL

which prints FALSE by default as 0,

which comes back from a FORM POST as string '0',

while PHP prints FALSE as empty string (!);

a similar problem is to preserve a NULL value through a FORM post....

adama at NO-UBE dot augustinefam dot org
24-May-2003 01:13


Just a correction to the 29-Apr-2003 10:49 posting. The first section of the comment, where



 $myBool = true ;  print( $myBool ) ;

 is indistinguishable from

 print( "" ) ;

 likewise,

 $myBool = false ; print( $myBool ) ;

 is indistinguishable from

 print( 1 ) ;



is backwards. It should actually be 



 $myBool = true ;  print( $myBool ) ;

 is indistinguishable from

 print( 1 ) ; //corrected

 likewise,

 $myBool = false ; print( $myBool ) ;

 is indistinguishable from

 print( "" ) ; //corrected



The posting makes a good point, though. Don't expect the contents of a string to mean something special. As the documentation states, any non-empty string is true, including "false" since it is simply a non-empty string.

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