Variable handling 函数
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is_bool

(PHP 4, PHP 5)

is_bool — 检测变量是否是布尔型

描述

bool is_bool ( mixed $var )

如果 var 是 boolean 则返回 TRUE。

Example #1 is_bool() 示例

<?php
$a = false;
$b = 0;

// 因为 $a 是布尔型，所以结果为真
if (is_bool($a)) {
    print "Yes, this is a boolean";
}

// 因为 $b 不是布尔型，所以结果为非真
if (is_bool($b)) {
    print "Yes, this is a boolean";
}
?>

参见 is_array()、is_float()、is_int()、is_integer()、is_string() 和 is_object()。

Variable handling 函数
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PHP手册
PHP手册 - N: 检测变量是否是布尔型

用户评论:

Spektrum (27-Jun-2011 09:21)

If you want to convert a string representation of a boolean ,like "yes", "on", "true", "false",etc..., to an actual boolean, you can try this:

<?php
$myString = "On";
$b = filter_var($myString, FILTER_VALIDATE_BOOLEAN);
?>

This will return TRUE for "1", "true", "on" and "yes". Returns FALSE otherwise.

kim at steinhaug dot com (26-Aug-2009 06:48)

Seems this is a most wanted function, so here is my version of it. I have been using this one for several years no and it works perfect for my needs. I have added "sloppy" human logic to it, and you could easily extend to your flavour. Like in norway some would use "ja" and "nei" instead of "yes" and "no".

<?php
/**
 * Checks a variable if it is true or false, humanlike.
 * We account for values as 'on', '1', '' and so on.   
 * Finally, for some reare occurencies we account with 
 * crazy logic to fit some arrays and objects.         
 *                                                     
 * @author Kim Steinhaug, <kim@steinhaug.com>          
 * @param mixed $var, the variable to check            
 *                                                     
 * Example:                                            
 * $test = 'true';                                     
 * if(_bool($test)){ echo 'true'; } else { echo 'false'; }
 */
function _bool($var){
  if(is_bool($var)){
    return $var;
  } else if($var === NULL || $var === 'NULL' || $var === 'null'){
    return false;
  } else if(is_string($var)){
    $var = trim($var);
    if($var=='false'){ return false;
    } else if($var=='true'){ return true;
    } else if($var=='no'){ return false;
    } else if($var=='yes'){ return true;
    } else if($var=='off'){ return false;
    } else if($var=='on'){ return true;
    } else if($var==''){ return false;
    } else if(ctype_digit($var)){
      if((int) $var)
        return true;
        else
        return false;
    } else { return true; }
  } else if(ctype_digit((string) $var)){
      if((int) $var)
        return true;
        else
        return false;
  } else if(is_array($var)){
    if(count($var))
      return true;
      else
      return false;
  } else if(is_object($var)){
    return true;// No reason to (bool) an object, we assume OK for crazy logic
  } else {
    return true;// Whatever came though must be something,  OK for crazy logic
  }
}
?>

moty66 at gmail dot com (20-Aug-2009 10:18)

Here is the function which I use when pasring boolean variables from config files

<?php
function boolVal($var) {
    switch ($var) {
        case $var == true:
        case $var == 1:
        // case $var == '1': // no need for this, because we used
                             // $val == 1 not $var === 1
        case strtolower($var) == 'true':
        case strtolower($var) == 'on':
        case strtolower($var) == 'yes':
        case strtolower($var) == 'y':
            $out = 1;
            break;
        default: $out = 0;
    }
   
    return $out;
}

?>

I am woundering why php does not have a function to do this

Motaz Abuthiab

sam+nospam at samuellevy dot com (02-Feb-2009 12:30)

Just another little function which doesn't exist yet, but I find mighty useful, especially when working with AJAX and APIs.

<?php
/** Checks a variable to see if it should be considered a boolean true or false.
 *     Also takes into account some text-based representations of true of false,
 *     such as 'false','N','yes','on','off', etc.
 * @author Samuel Levy <sam+nospam@samuellevy.com>
 * @param mixed $in The variable to check
 * @param bool $strict If set to false, consider everything that is not false to
 *                     be true.
 * @return bool The boolean equivalent or null
 */
function boolval($in, $strict=false) {
    $out = null;
    // if not strict, we only have to check if something is false
    if (in_array($in,array('false', 'False', 'FALSE', 'no', 'No', 'n', 'N', '0', 'off',
                           'Off', 'OFF', false, 0, null), true)) {
        $out = false;
    } else if ($strict) {
        // if strict, check the equivalent true values
        if (in_array($in,array('true', 'True', 'TRUE', 'yes', 'Yes', 'y', 'Y', '1',
                               'on', 'On', 'ON', true, 1), true)) {
            $out = true;
        }
    } else {
        // not strict? let the regular php bool check figure it out (will
        //     largely default to true)
        $out = ($in?true:false);
    }
    return $out;
}
?>

It may be pretty inefficient, but it does the job.

bb at kingdom dot cjb dot net (27-Jun-2007 10:57)

@ emmanuel del grande

You don't need to break when you return...

function bool($var) {
    switch (strtolower($var)) {
        case ("true"): return true;
        case ("false"): return false;
        default: die("whatever you want it to tell");
    }
}

kevin at metalaxe dot com (05-Jun-2007 09:32)

@ emanueledelgrande at email dot it

http://us.php.net/manual/en/language.types.type-juggling.php

(bool) or (boolean) is allowed for type casting a variable. No function like intval, etc but the functionality exists.

emanueledelgrande at email dot it (22-May-2007 05:12)

I think there's a hole in the PHP typecasting methods:
you have the (int) function, the (float) function and the (string) function, but no function to force a string variable into the boolean type.

It's obvious that forcing unconditionally the type of variables into arrays and objects is inappropriate, but boolean type is the most basic one for each programming language, that's why I guessed that a (bool) function already existed.

Moreover, with the increasing trend of RSS data streaming, the parsing of an XML string into an object often requires to typecast as boolean values the content of XML tags, normally returned as string by the object method get_content().

I wrote the following function, which also uses a "native PHP style" error message:

<?php
// strings tyecasting as boolean values:
function bool($var) {
    switch (strtolower($var)) {
        case ("true"):
            return true;
            break;
        case ("false"):
            return false;
            break;
        default:
            die("<br />\n<b>Warning:</b> Invalid argument supplied for ".__FUNCTION__." function in <b>".__FILE__."</b> on line <b>".__LINE__."</b>: the argument can contain only 'true' or 'false' values as a string.<br />\n");
    }
}
?>

Here it is a small example:

<?php
$xmlResponse = "<?xml version=\"1.0\" encoding=\"utf-8\"?>";
$xmlResponse .= "<Result>";
$xmlResponse .= "<AuthError>false</AuthError>";
$xmlResponse .= "<TransferStatus>true</TransferStatus>";
$xmlResponse .= "</Result>";

if (! $responseDoc = domxml_open_mem($xmlResponse, DOMXML_LOAD_PARSING, $XmlParsingError)) {
    echo "Error while parsing the XML string:<br />".print_r($XmlParsingError, TRUE);
} else {
    $ResultNode = $responseDoc->get_elements_by_tagname('Result');
   
    $AuthError = $ResultNode[0]->get_elements_by_tagname('AuthError');
    $auth_error = bool($AuthError[0]->get_content());
   
    $TransferStatus = $ResultNode[0]->get_elements_by_tagname('TransferStatus');
    $transfer_status = bool($TransferStatus[0]->get_content());
   
    if (! $auth_error) { echo "Auth OK<br />"; } else { echo "Auth error<br />"; }
    if ($transfer_status) { echo "Transfer OK<br />"; } else { echo "Transfer error<br />"; }
}

?>

It would be useful this function to be implemented in the core of PHP5.

(21-Apr-2006 12:12)

Small caveat to rh's post: back in PHP 3, "0" would be considered non-empty (i.e., empty would return false), even though (bool) on "0" would also evaluate to false; thus, they would not be complete opposites for someone using PHP 3.

rh at richardhoward dot net (22-May-2005 07:17)

punkpuke is wrong here; what he means to say is that empty($x) is the opposite of (bool)$x.  is_bool($x) returns true where $x === false.