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Subject: Re: Inconsistent float to string vs. string to float casting
From: salsi@icosaedro.it (Umberto Salsi)
Message-ID: <php.internals-103642@news.php.net>

cmbecker69@gmx.de ("Christoph M. Becker") wrote:

> Hi!
> 
> Regarding the decimal separator (aka. decimal point), the behavior of
> casting float to string is inconsistent with casting string to float.
> [...]

I'm shocked... Lot of code here assumes (float) does the exact reverse of
(string); forunately most servers are configures with the default locale
"C", but I'm still concerned for libraries portability.

Did you filed a bug for that?


Anyway, here is some test code I wrote:


<?php  // test-float-cast.php

/**
 * Performs string to float and float to string tests vs. locale.
 * @param string $loc LC_NUMERIC locale to set for the test.
 */
function test($loc)
{
=09if( setlocale(LC_NUMERIC, $loc) =3D=3D=3D FALSE )
=09=09throw new RuntimeException("setlocale() failed");
=09
=09// Cast float to string test:
=09$exp =3D "0.5";
=09$got =3D (string) 0.5;
=09if( $got !=3D=3D $exp )
=09=09echo "FAILED with LC_NUMERIC=3D$loc, (string) 0.5: got $got, exp $exp\=
n";
=09
=09// Cast string to float test:
=09$exp =3D 0.5;
=09$got =3D (float) "0.5";
=09if( $got !=3D=3D $exp )
=09=09echo "FAILED with LC_NUMERIC=3D$loc, (float) \"0.5\": got $got, exp $e=
xp\n";
=09
=09// printf() formatting of float:
=09$exp =3D "0.500000";
=09$got =3D sprintf("%f", 0.5);
=09if( $got !=3D=3D $exp )
=09=09echo "FAILED with LC_NUMERIC=3D$loc, sprintf(\"%f\", 0.5): got $got, e=
xp $exp\n";
}

test("C");
test("de");


Output:
FAILED with LC_NUMERIC=3Dde, (string) 0.5: got 0,5, exp 0.5
FAILED with LC_NUMERIC=3Dde, sprintf("%f", 0.5): got 0,500000, exp 0.500000

The second failed test is expected, as printf, scanf and co. are intended
to be locale-aware.

But the first one? Is there any simple, efficient and safe way to convert
back a string into float?


Regards,
 ___ 
/_|_\  Umberto Salsi
\/_\/  www.icosaedro.it