Note, that if no connection is open, mysqli_real_escape_string() will return an empty string!
mysqli::real_escape_string
mysqli_real_escape_string
(PHP 5, PHP 7)
mysqli::real_escape_string -- mysqli_real_escape_string — Escapes special characters in a string for use in an SQL statement, taking into account the current charset of the connection
Description
Object oriented style
string mysqli::real_escape_string
( string
$escapestr
)Procedural style
This function is used to create a legal SQL string that you can use in an SQL statement. The given string is encoded to an escaped SQL string, taking into account the current character set of the connection.
Caution
Security: the default character set
The character set must be set either at the server level, or with the API function mysqli_set_charset() for it to affect mysqli_real_escape_string(). See the concepts section on character sets for more information.
Parameters
-
link -
Procedural style only: A link identifier returned by mysqli_connect() or mysqli_init()
-
escapestr -
The string to be escaped.
Characters encoded are NUL (ASCII 0), \n, \r, \, ', ", and Control-Z.
Return Values
Returns an escaped string.
Examples
Example #1 mysqli::real_escape_string() example
Object oriented style
<?php
$mysqli = new mysqli("localhost", "my_user", "my_password", "world");
/* check connection */
if (mysqli_connect_errno()) {
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
$mysqli->query("CREATE TEMPORARY TABLE myCity LIKE City");
$city = "'s Hertogenbosch";
/* this query will fail, cause we didn't escape $city */
if (!$mysqli->query("INSERT into myCity (Name) VALUES ('$city')")) {
printf("Error: %s\n", $mysqli->sqlstate);
}
$city = $mysqli->real_escape_string($city);
/* this query with escaped $city will work */
if ($mysqli->query("INSERT into myCity (Name) VALUES ('$city')")) {
printf("%d Row inserted.\n", $mysqli->affected_rows);
}
$mysqli->close();
?>
Procedural style
<?php
$link = mysqli_connect("localhost", "my_user", "my_password", "world");
/* check connection */
if (mysqli_connect_errno()) {
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
mysqli_query($link, "CREATE TEMPORARY TABLE myCity LIKE City");
$city = "'s Hertogenbosch";
/* this query will fail, cause we didn't escape $city */
if (!mysqli_query($link, "INSERT into myCity (Name) VALUES ('$city')")) {
printf("Error: %s\n", mysqli_sqlstate($link));
}
$city = mysqli_real_escape_string($link, $city);
/* this query with escaped $city will work */
if (mysqli_query($link, "INSERT into myCity (Name) VALUES ('$city')")) {
printf("%d Row inserted.\n", mysqli_affected_rows($link));
}
mysqli_close($link);
?>
The above examples will output:
Error: 42000 1 Row inserted.
Notes
Note:
For those accustomed to using mysql_real_escape_string(), note that the arguments of mysqli_real_escape_string() differ from what mysql_real_escape_string() expects. The
linkidentifier comes first in mysqli_real_escape_string(), whereas the string to be escaped comes first in mysql_real_escape_string().
See Also
- mysqli_set_charset() - Sets the default client character set
- mysqli_character_set_name() - Returns the default character set for the database connection
add a note
User Contributed Notes 10 notes
tobias_demuth at web dot de ¶
10 years ago
Josef Toman ¶
6 years ago
For percent sign and underscore I use this:
<?php
$more_escaped = addcslashes($escaped, '%_');
?>
James ¶
2 months ago
To escape for the purposes of having your queries made successfully, and to prevent SQLi (SQL injection)/stored and/or reflected XSS, it's a good idea to go with the basics first, then make sure nothing gets in that can be used for SQLi or stored/reflected XSS, or even worse, loading remote images and scripts.
For example:
<?php
// Assume this is a simple comments form with a name and comment.
$name = mysqli_real_escape_string($conn, $_POST['name']);
$comments = mysqli_real_escape_string($conn, $_POST['comments']);
// Here is where most of the action happens. But see note below
// on dumping back out from the database
// We should use the ENT_QUOTES flag second parameter...
$name = htmlspecialchars($name);
$comments = htmlspecialchars($comments);
$insert_sql = "INSERT INTO tbl_comments ( c_id, c_name, c_comments ) VALUES ( DEFAULT, '" . $name . "', '" . $comments . "')";
$res = mysqli_query($conn, $insert_sql);
if ( $res === false ) {
// Something went wrong, handle it
}
// Now output page showing comments
?>
// Assume we're in a table with each row containing a name and comment
<?php
$res = mysqli_query($conn, "SELECT c_name, c_comments FROM tbl_comments ORDER BY c_name ASC");
if ( $res === false )
// Something went wrong
// Or as you like...
while ( $row = mysqli_fetch_array($res, MYSQLI_BOTH) ) {
// This will output safe HTML entities if they went in
// They will be displayed, but not interpreted
echo "<tr><td>" . $row['c_name'] . "</td>";
echo "<td>" . $row['c_comments'] . "</td></tr>";
// BUT, if you make this mistake...
echo "<tr><td>" . htmlspecialchars_decode($row['c_name']) . "</td>";
echo "<td>" . htmlspecialchars_decode($row['c_comments']) . "</td></tr>";
// ... then your entities will reflect back as the characters, so
// input such as this: "><img src=x onerror=alert('xss')>
// will display the 'xss' in an alert box in the browser.
}
mysqli_free_result($res);
mysqli_close($conn);
?>
In most cases, you wouldn't want to go way overboard sanitizing untrusted user input, for instance:
<?php
$my_input = htmlspecialchars( strip_tags($_POST['foo']) );
?>
This will junk a lot of input you might actually want, if you're rolling your own forum or comments section and it's for web developers, for example. On the other hand, if legitimate users are never going to enter anything other than text, never HTML tags or anything else, it's not a bad idea.
The take-away is that mysqli_real_escape_string() is not good enough, and being overly-aggressive in sanitizing input may not be what you want.
Be aware that in the above example, it will protect you from sqli (run sqlmap on all your input fields and forms to check) but it won't protect your database from being filled with junk, effectively DoS'ing your Web app in the process.
So after protecting against SQLi, even if you're behind CloudFlare and take other measures to protect your databases, there's still effectively a DoS attack that could slow down your Web App for legitimate users and make it a nightmare filled with rubbish that some poor maintainer has to clean out, if you don't take other measures.
So aside from escaping your stings, and protecting against SQLi and stored/reflected XSS, and maliciously loaded images or JS, there's also checking your input to see if it makes sense, so you don't get a database full of rubbish!
It just never ends... :-)
zanferrari at gmail dot com ¶
2 years ago
When I submit data through Ajax I use a little function to reconvert the encoded chars to their original value. After that I do the escaping. Here the function:
function my_htmlentities($input){
$string = htmlentities($input,ENT_NOQUOTES,'UTF-8');
$string = str_replace('€',chr(128),$string);
$string = html_entity_decode($string,ENT_NOQUOTES,'ISO-8859-15');
return $string;
}
G.Zanferrari
arnoud at procurios dot nl ¶
11 years ago
Note that this function will NOT escape _ (underscore) and % (percent) signs, which have special meanings in LIKE clauses.
As far as I know there is no function to do this, so you have to escape them yourself by adding a backslash in front of them.
Anonymous ¶
1 year ago
If you wonder why (besides \, ' and ") NUL (ASCII 0), \n, \r, and Control-Z are escaped: it is not to prevent sql injection, but to prevent your sql logfile to get unreadable.
dave at mausner.us ¶
5 years ago
You can avoid all character escaping issues (on the PHP side) if you use prepare() and bind_param(), as an alternative to placing arbitrary string values in SQL statements. This works because bound parameter values are NOT passed via the SQL statement syntax.
anon ¶
9 months ago
if ($_SERVER['REQUEST_METHOD'] == "GET" && isset($_GET['value'])) {
$id = trim($link->real_escape_string($_GET['value']));
$sql = "DELETE FROM database WHERE IDItem = $id";
if (!$res = $link->query($sql)) {
$_SESSION['alertify'] = 'alertify.error("' . $link->error . '")';
} else {
$_SESSION['alertify'] = 'alertify.success("' . $value . ' was succesfully deleted")';
}
}
kit dot lester at mail dot com ¶
3 years ago
A PHP application I'm working on has many pages which (long story) need to share a PHP API that looks after a MySQL database. Easiest way was to have the app pages AJAX to the API .PHPs.
That means having the JavaScript of the AJAX encodeURIComponent(...) relevant bits of any data to be sent via HTTP POST and GET requests - space as %20 and so on.
But the SQL also needed real_escape_string(...) of the same data.
So I had the issue of whether to do the real_escape_string *before* or *after* encodeURIComponent? in other words in the application PHP or API PHP? Do either of the encodings mangle the other?
The real_escape_string would be "cleaner" in the API, both in principle, and because it needs an instance of mysqli class and there are are unlikely to be instances in the app.
(real_escape_string needs an instance because it's not a *static* function - I don't know why).
But I suspect that "in the API" is the mangle-avoiding place: the JavaScript encode gets undone by the HTTP call to whichever API element, then the element can safely real_escape_string what is to be put into the database.
Comments would be appreciated.
nmmm at nmmm dot nu ¶
2 years ago
Note unlike PDO string escape, MySQLi does not include apostrophes.
So, you probably want something like this:
function escape($s){
$s = $this->mysqli->real_escape_string($s);
return "'$s'";
}
