Re: [PHP] How can an elephant count for nothing?
I guess the main reason for PHP to behave like this is to make life easier for many everyday situations. EXAMPLE: User input via GET or POST - usually string You compare it to some value - int/string or whatever So if a user posts '17' (string) and you compare it to 17 (int), unless you are using ===, PHP won't complain. -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] How can an elephant count for nothing?
While PHP has a lot of nice features, it also has some traps which I am forever falling into. One which I find particularly hard to understand is how mixed mode comparisons work. For instance $string = 'elephant'; If($string == 0) returns true; If($string != 0) returns false; If($string === 0) returns false; I know that in this case I should use 'If($string == '')', but I still manage to forget. Can anyone explain clearly why comparing a string with zero gives this apparently anomalous result? when comparing string with integer, the interpreter first converts string into an integer before comparison takes place. Virgil http://www.jampmark.com -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
[PHP] How can an elephant count for nothing?
While PHP has a lot of nice features, it also has some traps which I am forever falling into. One which I find particularly hard to understand is how mixed mode comparisons work. For instance $string = 'elephant'; If($string == 0) returns true; If($string != 0) returns false; If($string === 0) returns false; I know that in this case I should use 'If($string == '')', but I still manage to forget. Can anyone explain clearly why comparing a string with zero gives this apparently anomalous result? -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] How can an elephant count for nothing?
Clancy wrote: While PHP has a lot of nice features, it also has some traps which I am forever falling into. One which I find particularly hard to understand is how mixed mode comparisons work. For instance $string = 'elephant'; If($string == 0) returns true; If($string != 0) returns false; If($string === 0) returns false; I know that in this case I should use 'If($string == '')', but I still manage to forget. Can anyone explain clearly why comparing a string with zero gives this apparently anomalous result? I'm not certain, but I suspect it's because the interpreter attempts to convert elephant to an integer first. /Per -- Per Jessen, Zürich (-0.6°C) -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] How can an elephant count for nothing?
Clancy schreef: While PHP has a lot of nice features, it also has some traps which I am forever falling into. One which I find particularly hard to understand is how mixed mode comparisons work. For instance $string = 'elephant'; If($string == 0) returns true; If($string != 0) returns false; If($string === 0) returns false; I know that in this case I should use 'If($string == '')', but I still manage to forget. Can anyone explain clearly why comparing a string with zero gives this apparently anomalous result? it's called auto-casting (or auto-typecasting) and it's 'by design' ... welcome to the world of dynamic typing. try this to see it working: php -r ' var_dump((integer)elephant); var_dump((float)elephant); var_dump((bool)elephant); var_dump((array)elephant); var_dump((object)elephant); var_dump((bool)(integer)elephant); ' you can avoid auto-casting if needed, in a variety of ways: php -r ' $foo = elephant; if (!empty($foo)) echo $foo found!\n; if (strlen($foo)) echo $foo found!\n; if (is_string($foo) strlen($foo)) echo $foo found!\n; if ($foo !== ) echo $foo found!\n; if ($foo === elephant) echo $foo found!\n; ' those last 2 show how to use 'type-checked' equality testing. -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] How can an elephant count for nothing?
Can anyone explain clearly why comparing a string with zero gives this apparently anomalous result? ?php $string = 'oleyphoont'; var_dump((int)$string, $string == 0, $string == 1); ? -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] How can an elephant count for nothing?
Have you tried with a mouse? -- Dotan Cohen http://what-is-what.com http://gibberish.co.il א-ב-ג-ד-ה-ו-ז-ח-ט-י-ך-כ-ל-ם-מ-ן-נ-ס-ע-ף-פ-ץ-צ-ק-ר-ש-ת ا-ب-ت-ث-ج-ح-خ-د-ذ-ر-ز-س-ش-ص-ض-ط-ظ-ع-غ-ف-ق-ك-ل-م-ن-ه-و-ي А-Б-В-Г-Д-Е-Ё-Ж-З-И-Й-К-Л-М-Н-О-П-Р-С-Т-У-Ф-Х-Ц-Ч-Ш-Щ-Ъ-Ы-Ь-Э-Ю-Я а-б-в-г-д-е-ё-ж-з-и-й-к-л-м-н-о-п-р-с-т-у-ф-х-ц-ч-ш-щ-ъ-ы-ь-э-ю-я ä-ö-ü-ß-Ä-Ö-Ü
Re: [PHP] How can an elephant count for nothing?
Jochem Maas wrote:
Clancy schreef:
While PHP has a lot of nice features, it also has some traps which I am forever falling
into. One which I find particularly hard to understand is how mixed mode comparisons work.
For instance
$string = 'elephant';
If($string == 0) returns true;
If($string != 0) returns false;
If($string === 0) returns false;
I know that in this case I should use 'If($string == '')', but I still manage to forget.
Can anyone explain clearly why comparing a string with zero gives this apparently
anomalous result?
it's called auto-casting (or auto-typecasting) and it's 'by design'
... welcome to the world of dynamic typing.
try this to see it working:
php -r '
var_dump((integer)"elephant");
var_dump((float)"elephant");
var_dump((bool)"elephant");
var_dump((array)"elephant");
var_dump((object)"elephant");
var_dump((bool)(integer)"elephant");
'
you can avoid auto-casting if needed, in a variety of ways:
php -r '
$foo = "elephant";
if (!empty($foo))
echo "$foo found!\n";
if (strlen($foo))
echo "$foo found!\n";
if (is_string($foo) strlen($foo))
echo "$foo found!\n";
if ($foo !== "")
echo "$foo found!\n";
if ($foo === "elephant")
echo "$foo found!\n";
'
those last 2 show how to use 'type-checked' equality
testing.
because intval("elephant") == 0;
intval will convert the string into integer , Strings
will most likely return 0 although this depends on the leftmost
characters of the string.
--
Laruence's Signature
惠
新宸 xinchen.hui | SYS | (+8610)82602112-7974 | :laruence
Re: [PHP] How can an elephant count for nothing?
惠新宸 wrote: Jochem Maas wrote: Clancy schreef: While PHP has a lot of nice features, it also has some traps which I am forever falling into. One which I find particularly hard to understand is how mixed mode comparisons work. For instance $string = 'elephant'; If($string == 0) returns true; If($string != 0) returns false; If($string === 0) returns false; I know that in this case I should use 'If($string == '')', but I still manage to forget. Can anyone explain clearly why comparing a string with zero gives this apparently anomalous result? it's called auto-casting (or auto-typecasting) and it's 'by design' ... welcome to the world of dynamic typing. try this to see it working: php -r ' var_dump((integer)elephant); var_dump((float)elephant); var_dump((bool)elephant); var_dump((array)elephant); var_dump((object)elephant); var_dump((bool)(integer)elephant); ' you can avoid auto-casting if needed, in a variety of ways: php -r ' $foo = elephant; if (!empty($foo)) echo $foo found!\n; if (strlen($foo)) echo $foo found!\n; if (is_string($foo) strlen($foo)) echo $foo found!\n; if ($foo !== ) echo $foo found!\n; if ($foo === elephant) echo $foo found!\n; ' those last 2 show how to use 'type-checked' equality testing. because intval(elephant) == 0; intval will convert the string into integer , Strings will most likely return 0 although this depends on the leftmost characters of the string. -- Baidu惠新宸 xinchen.hui* | * SYS *| * (+8610)82602112-7974 *|* Hi:laruence '2 elephants' != 0 -- Thanks! -Shawn http://www.spidean.com -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] How can an elephant count for nothing?
On Thu, 2009-02-12 at 13:12 +0200, Dotan Cohen wrote: Have you tried with a mouse? Non-strings equate to a boolean value of 1 when they are converted to a boolean value automatically (in the case of comparison queries) when they contain a value. Strings of 0 length are converted to a 0. In useful terms, 1 is true and 0 is false in the PHP world. As PHP is a loose-typed language you should really use the === operator if you need to compare variable mathc and type match. Ash www.ashleysheridan.co.uk -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] How can an elephant count for nothing?
On Thu, 12 Feb 2009 23:47:31 +0800, huixinc...@baidu.com (???) wrote: Jochem Maas wrote: Clancy schreef: While PHP has a lot of nice features, it also has some traps which I am forever falling into. One which I find particularly hard to understand is how mixed mode comparisons work. . you can avoid auto-casting if needed, in a variety of ways: php -r ' $foo = elephant; if (!empty($foo)) echo $foo found!\n; if (strlen($foo)) echo $foo found!\n; if (is_string($foo) strlen($foo)) echo $foo found!\n; if ($foo !== ) echo $foo found!\n; if ($foo === elephant) echo $foo found!\n; ' those last 2 show how to use 'type-checked' equality testing. because intval(elephant) == 0; intval will convert the string into integer , Strings will most likely return 0 although this depends on the leftmost characters of the string. This seems to be the nearest to the correct answer. In fact it appears that if you compare a string with an integer the effective value of the string is the value of the first character(s), if it/they are integers, or zero. elephant == 0; true an elephant == 0; true 1 elephant == 0; false 0 elephants == 0; true a herd of elephants == 0; true 7 elephants == 7; true elephants == ; true The next question is ' how is the order of conversion determined?' I thought it might have converted the second element to the same type as the first element, so I reversed the comparison, but I got exactly the same results, so perhaps it converts from the more complex type to the simpler type. Clearly the lesson is to be learnt is not to compare disparate types, unless you really have to. One situation where this is unavoidable is if you are searching an arbitrary set of strings for a given word. In this case it is essential to do the exact comparison, or you will get erroneous results. Thank you all for your suggestions. -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
