| Re: Implied cast differs from explicit cast [message #176669 is a reply to message #176657] |
Mon, 16 January 2012 10:48   |
alvaro.NOSPAMTHANX
Messages: 277
Registered: September 2010
Karma:
|
Senior Member |
|
|
El 16/01/2012 2:10, lb escribió/wrote:
> When converting some strings to int (or double), I am finding that
> an implied cast get different results from explicit cast. This happens
> when the string contains a hex representation. The implied cast converts
> the hex value, but the explicit cast returns 0. The manual under "String
> conversion to numbers" says nothing about it allowing hex values. This is
> with PHP-5.3.9 and older.
>
> Script:
> <?php
> $s1 = '0x12';
> $t1 = $s1 + 0;
> echo "Implied cast t1=$t1\n";
> $t2 = (int)$s1 + 0;
> echo "Explicit cast t2=$t2\n";
>
> Output:
> Implied cast t1=18
> Explicit cast t2=0
>
>
> I think this is odd. A side problem is that is_numeric('0x12') is true, but
> ((int)'0x12') is 0. Does anyone think this a bug?
Interesting subject... There are actually two different sections in the
PHP manual:
*************************************************************************
Explicit cast:
http://es2.php.net/manual/en/language.types.integer.php#language.types.inte ger.casting
«To explicitly convert a value to integer, use either the (int) or
(integer) casts. [...] A value can also be converted to integer with the
intval() function.»
It admit it's not 100% clear but I have the impression that the
underlying code is just the same and intval():
http://es2.php.net/manual/en/function.intval.php>
*************************************************************************
Implicit cast:
http://es2.php.net/manual/en/language.types.string.php#language.types.strin g.conversion
«When a string is evaluated in a numeric context, the resulting value
and type are determined as follows.»
First difference is that you don't necessarily get an integer:
«If the string does not contain any of the characters '.', 'e', or 'E'
and the numeric value fits into integer type limits (as defined by
PHP_INT_MAX), the string will be evaluated as an integer. In all other
cases it will be evaluated as a float.»
Second difference is that a standard C library is mentioned:
«For more information on this conversion, see the Unix manual page for
strtod(3).»
.... thus we can get further details:
http://linux.die.net/man/3/strtod
«The expected form of the (initial portion of the) string is optional
leading white space as recognized by isspace(3), an optional plus ('+')
or minus sign ('-') and then either (i) a decimal number, or (ii) a
hexadecimal number, or (iii) an infinity, or (iv) a NAN (not-a-number).»
*************************************************************************
I believe the most relevant difference is that:
- intval() accepts any base but does not guess (defaults to 10)
- strtod() only accepts base 10 and 16 and does guess
.... which explains your issue.
--
-- http://alvaro.es - Álvaro G. Vicario - Burgos, Spain
-- Mi sitio sobre programación web: http://borrame.com
-- Mi web de humor satinado: http://www.demogracia.com
--
|
|
|
|
Calendar
Search
Help
Members
Register
Login
Home
]