| Re: empty - not empty() [message #176318 is a reply to message #176312] |
Tue, 20 December 2011 23:44  |
bill
Messages: 310
Registered: October 2010
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Senior Member |
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On 12/20/2011 11:40 AM, M. Strobel wrote:
> Am 20.12.2011 14:14, schrieb bill:
>> On 12/19/2011 8:14 PM, Chuck Anderson wrote:
>>> J.O. Aho wrote:
>>>> bill wrote:
>>>> > searching the manual gives lots of hits, none of which appear
>>>> > relevant (at
>>>> > least by the title).
>>>> >
>>>> > I had the following code in a scheduling class:
>>>> >
>>>> > if ($ptNum == "empty") {
>>>> > $ptNum = 0;
>>>> > $status= "e";
>>>> > }
>>>> >
>>>> > I pass the string "empty" to the function as a patient number
>>>> > if we are
>>>> > creating an empty appointment slot.
>>>> >
>>>> > now, this fails because with a patient number of 0 the if
>>>> > returns true.
>>>> >
>>>> > I am aware of the function empty() that would work like that,
>>>> > but do not
>>>> > understand why the compare fails with the constant, "empty."
>>>>
>>>> I assume you are comparing 0 and not the string "0", this makes
>>>> you are comparing integer with string, there ain't any type
>>>> conversion done.
>>>
>>> Actually, it is because there *is* an automatic type conversion
>>> done when comparing a string to an int.
>>>
>>> "If you compare a number with a string or the comparison involves
>>> numerical strings, then each string is converted to a number and
>>> the comparison performed numerically."
>>>
>>> ... http://us.php.net/manual/en/language.operators.comparison.php
>>>
>>>> The zero is always equal to a string,
>>>
>>> Not true.
>>> "If the string starts with valid numeric data, this will be the
>>> value used. Otherwise, the value will be 0 (zero)."
>>>
>>> ....
>>> http://us.php.net/manual/en/language.types.string.php#language.types.string .conversion
>>>
>>>
>>>
>>>> there is a slightly more information at
>>>>
>>>> http://php.net/manual/en/language.operators.comparison.php
>>>
>>> You might want to take a closer look at that page.
>>>
>>> The literal string "empty" does not begin with a numerical
>>> character so it will be converted to the integer 0.
>>
>> Thank you, that makes sense.
>>>
>>>> > the regular compare is true with the numeric value of zero.
>>>> I fixed the function by making it a strict compare, but would
>>>> like to know why
>>>>
>>>> I would say it's not the right way to compare, use strcmp,
>>>> is_numeric and so on, to make a proper compare instead of using
>>>> the comparison operator.
>>>>
>>>
>>> I think you have that backwards. The identical (strict)
>>> comparison is far more efficient than a function call and this
>>> it's intended usage. "===" compares value and type (so no type
>>> conversion). Hence the string "empty" does not equal (===) the
>>> integer 0.
>>>
>> Glad to know that I stumbled onto the right way to do it.
>> Your comments are much appreciated and enlightening.
>>
>> bill
>>
>
> Comparison in PHP, like in many scripting languages, has its
> special cases, the same as javascript.
>
> There is one link to php comparison that I use very often, and it
> is very difficult to find, you will see very concise tables about
> the different compares:
>
> http://de3.php.net/manual/en/types.comparisons.php
thank you, that is very helpful.
bill
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