Q: How do I use addslashes() and stripslashes() when dealing with HTML
forms and database INSERTs, UPDATEs and SELECTs?
Q: How do I handle single quotes in user input, I am getting errors
trying
to INSERT and UPDATE.
Q: Why do I have backslashes in my form data?
Q: What do I need to do to "sanitize" user input so it is
database-safe?
A. It depends on the setting of the php.ini directive
"magic_quotes_gpc". By default, magic_quotes_gpc is On.
If magic_quotes_gpc is On:
Use stripslashes() for data which originates from an HTML form and is
shown in an HTML page after a roundtrip to the server.
Do not use addslashes().
If magic_quotes_gpc is Off:
Use addslashes() when INSERTing or UPDATEing data into the database.
Do not use stripslashes().
You can check the magic_quotes_gpc setting with the
get_magic_quotes_gpc() function.
Contrary to popular belief, it should never be necessary to use
stripslashes() on data which originates from a database SELECT. The
slashes which are added manually with addslashes(), or automagically
when magic_quotes_gpc is On, are only used to properly escape the data
before an INSERT or UPDATE and are themselves not stored in the
database.
Refer:
http://www.php.net/addslashes http://www.php.net/stripslashes http://www.php.net/get_magic_quotes_gpc
------------------
Q. I'm getting extra \ in my form field
A. You are using Get/Post/Cookie (GPC) data without stripping the
magically [1] added quotes (which are on by default).
If aren't getting the data from GPC magic_quotes_runtime might be
on (off by default)
Q. When to escape?
A. Only use the right escape method at the moment it is needed.
What the right escape method actually is depends on where the data
will be used. If you are inserting the string $bar into eg mysql
you should escape it with mysql_real_escape_string() [2]
$query="UPDATE foo SET bar='".mysql_real_escape_string($bar)."'";
the same base shoule be htmlescaped [3] when used in html
echo "<a
href='foo.php?bar=".urlencode($bar)."'>".htmlspeci alchars($bar,ENT_QUOTES)."</a>";
(also note that $bar needs to be urlescaped [4] if used in an URL)
So in oorder to make this work you should always keep the raw
unescaped values (this is why (IMHO) magic_quotes is evil). To make
sure you are actually working with the raw values you should
sanitize
GPC data with something like this (untested and incomplete code):
function slashed($t)
{
if(get_magic_quotes_gpc())
{
if(is_array($t) && count($t))
for($i=0;$i<count($t);$i++)
$t[$i]=slashed($t[$i]);
else
$t=stripslashes($t);
}
return $t;
}
$_GET=slashed($_GET);
$_POST=slashed($_POST);
$_REQUEST=slashed($_REQUEST);
$_COOKIE=slashed($_COOKIE);
Q. When and how to sanitize data
A. Like escaping it depends on usage. If know data in a sql row should
be an int, you could do something like this:
$query="UPDATE foo SET bar='".((int)$bar)."'";
If the data should contain a dutch style postalcode:
if(!preg_match("/^\d{4}\s*[A-Za-z]{2}$/",trim($zip))
die("error in zip");
But IMHO you shouldn't try to fix obviously wrong data.
[1]
http://www.php.net/magicquotes
[2]
http://www.php.net/mysql_real_escape_string
[3]
http://www.php.net/htmlspecialchars
[4]
http://www.php.net/urlencode
+++++
@revision 1 Initial
@revision 2 Merged Kenneth Downs comments. Shortened document URLs
@revision 3 Shortened document URLs. Brining Daniel Tryba's
<news:42*********************@news6.xs4all.nl> entry here so that it
won't be get orphaned
@author Jan Pieter Kunst, Kenneth Downs, Daniel Tryba
@todo grammar checking by native English speaker. Maybe the 'Q' should
be something like "Why do I have backslashes in my form data"? Not
sure.
@todo Bring this question to main FAQ Thread. (missed this one in Rev
5). Merge the Q&A's appropriately
