型
At http://www.blueshoes.org/en/developer/syntax_exam/, is available a test where you can try your knowledge about boolean expressions. Hope it helps!
論理型 (boolean)
論理型は、最も簡単な型です。boolean は、真偽の値を表します。 この値は、TRUE または FALSE のどちらかになります。
注意: 論理型は、PHP 4 で導入されました。
構文
boolean リテラルを指定するには、キーワード TRUE または FALSE を指定してください。 両方とも大文字小文字に依存しません。
<?php
$foo = True; // 値TRUEを$fooに代入する
?>
通常、boolean 型の値を返す演算子を使用してから、 制御構造にその結果を渡します。
<?php
// == は、boolean型を返す演算子
if ($action == "show_version") {
echo "バージョンは1.23です。";
}
// これは冗長
if ($show_separators == TRUE) {
echo "<hr>\n";
}
// 上の例は次のように簡単に書くことができます。
if ($show_separators) {
echo "<hr>\n";
}
?>
boolean への変換
boolean に明示的に変換を行うには、キャスト (bool) または (boolean) を使用します。しかし、演算子、関数、制御構造が boolean 型の引数を必要とする場合には、値は自動的に変換されるため、 多くの場合はキャストは不要です。
型の相互変換 も参照ください。
boolean に変換する場合、次の値は FALSE とみなされます。
- boolean の FALSE
- integer の 0 (ゼロ)
- float の 0.0 (ゼロ)
- 空の文字列、 および文字列の "0"
- 要素の数がゼロである 配列
- メンバ変数の数がゼロである オブジェクト (PHP 4のみ)
- 特別な値 NULL (値がセットされていない変数を含む)
- 空のタグから作成された SimpleXML オブジェクト
その他の値は全て TRUE とみなされます (全ての resourceを含みます)。
警告
-1 は、他のゼロでない数と同様に (正負によらず) TRUE とみなされます。
<?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論理型 (boolean)
maykelsb [ta] yahoo [tod] com [tod] br
01-Feb-2008 01:54
01-Feb-2008 01:54
Wackzingo
27-Jan-2008 04:39
27-Jan-2008 04:39
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.
$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
16-Jan-2008 01:00
16-Jan-2008 01:00
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 05:05
06-Jan-2008 05:05
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 07:37
27-Sep-2007 07:37
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');
$s = !!"testing"; // This will === true; (as expected)
/*
Note: normal casting rules apply so a !!"0" would evaluate to an === false
*/
?>
openspecies
13-Jul-2007 06:22
13-Jul-2007 06:22
function is_odd($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 08:03
23-May-2007 08:03
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
30-Apr-2007 12:21
30-Apr-2007 12:21
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 05:45
Jasper probably meant:
$a = 2;
$b = 3;
$aBiggerThanB = $a > $b;
andy at txtnation dot com
25-Feb-2007 07:31
25-Feb-2007 07:31
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 10:51
05-Jun-2006 10:51
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";
?>