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Re: empty - not empty()

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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.

>> 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.

-- 
*****************************
 Chuck Anderson • Boulder, CO
  http://cycletourist.com
 Turn Off, Tune Out, Drop In
*****************************

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Thread

empty - not empty() bill <nobody@spamcop.net> - 2011-12-19 10:09 -0500
  Re: empty - not empty() "J.O. Aho" <user@example.net> - 2011-12-19 18:48 +0100
    Re: empty - not empty() Chuck Anderson <cycletourist@invalid.invalid> - 2011-12-19 18:14 -0700
      Re: empty - not empty() bill <nobody@spamcop.net> - 2011-12-20 08:14 -0500
        Re: empty - not empty() "M. Strobel" <sorry_no_mail_here@nowhere.dee> - 2011-12-20 17:40 +0100
          Re: empty - not empty() bill <nobody@spamcop.net> - 2011-12-20 18:44 -0500

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