IMHO this is not a bug. However, I leave it to Johannes/Andrey to review and close the issue.

bind_param() is about binding variables not constant values:
"stmt->bind_param() ? Binds variables to a prepared statement as parameters".

The signature of the function tells you that you have to pass input parameter variables by reference:
bool mysqli_stmt_bind_param  ( mysqli_stmt $stmt  , string $types  , mixed &$var1  [, mixed &$...  ] )

Using references to "real variables" instead of "constant values" does work fine. 

Note the small difference between references to variables in PHP and memory pointer in C. In PHP your references have to point to existing variables. You can't make them point to arbitrary places in memory like in C. If a PHP function asks you to provide a reference to an existing variable, you must not try to pass a (constant) value to it. But this is exactly what you do in your call_user_func_array() example.

Use the function like this:

$int = 1;
mysqli_stmt_bind_param($stmt, 'i', $int);
$stmt->bind_param('i', $int);

And, if you want to use call_user_func_array(), the syntax is:

$int = 1;
$format = 'i';
$params = array(0 => $format, 1 => &$int);
call_user_func_array('mysqli_stmt_bind_param', $params);
call_user_func_array(array($stmt, 'bind_param'), $params);

// - or - 

$int = 1;
$params = array(0 => 'i', 1 => &$int);
call_user_func_array('mysqli_stmt_bind_param', $params);
call_user_func_array(array($stmt, 'bind_param'), $params);

// - or - 

$int = 1;
call_user_func_array('mysqli_stmt_bind_param', array('i', &$int));

Neither of the following does work with PHP 5_3. Recall that the function is about binding variables not binding (constant) values, recall that you have to pass a reference to a variable:

WRONG: mysqli_stmt_bind_param($stmt, 'i', 1);
WRONG: call_user_func_array('mysqli_stmt_bind_param', array('i', 1));

Forgot to say: IMHO this should be reported over at Zend Framework but not here. I've tested 5_2, 5_3, 6_0 and I see no differences in handling.

Hold on, a PHP internals expert should have a look. sort() is another example of a function which uses pass by reference.

The manual says about call_user_func_array():
"Note: Referenced variables in param_arr  are passed to the function by a reference, others are passed by a value. In other words, it does not depend on the function signature whether the parameter is passed by a value or by a reference. "

From a discussion with Johannes:

sapi/cli/php -r '$a = array(2, 1); var_dump(call_user_func_array("sort", array($a)));'

PHP 5.2 -> bool(true)
PHP 5.3 -> NULL

Looks like its not a mysqli issue but rather a general PHP issue.

I understand now why this isn't supposed to work, but it is with PHP 5.2  

This "new" behavior make this bind_param function a lot less attractive when using it in situations like ZF does: binding an unknown number of parameters to a statement (like in any Object-Relational Mapper). There is no way now other than using the very ugly eval() to dynamically create the required number of variables to bind with bind_param.

Besides, this method is never suppposed to return NULL, (doc says boolean return, TRUE on success, FALSE on failure). This is why I almost immediately thought that was a bug.

Another fact is the doc example is very strange with calling stmt_bind_param with variables _before_ having them created. This is very "special" coding style.

My final thought: The old behavior (PHP 5.2) is really useful because there is no other way to do the same with the new one except using eval() as an ugly workaround, and the new behavior is returning an undocumented (and useless) value.

I really don't know if I have to file a new bug report in 5_2 about the incorrect behavior of bind_param (which is IMHO the most useful one).

Thank you anyway for the explanation, I'm now waiting for the final opinions about this.

It seems you posted your comment before I finished writing mine. Good to see that I'm not going crazy because I just tested the case with sort and got the same bug as you! Should I change the category for this bug? If so, which one?

I suggest that we leave the bug status as is for the moment. From what I know some PHP hackers are already discussing the case and Johannes (Schl?ter) will take care that it does not get forgotten.

Your comment on the example in the documentation is welcome. I agree with you that, for example, a code comment might be help beginners understand the example better.

The manual example works because PHP implicitly creates a variable for you whenever you start to use one. There's no need in PHP to sort of declare a variable before you use it. So, on the one hand it might make sense to change the example like this:

$bind_param = null;
mysqli_stmt_bind_param(..., &$bind_param)

... on the other hand, there's no need for the assignment operation. Its a PHP feature that you can start using variables ad-hoc and PHP does all the magic for you behind the scenes to make this possible. In that sense the extra line is nothing but overhead. 

A beginner might appreciate to see the line '$bind_param = null' before the call to mysqli_stmt_bind_param() to sort of better visualize the "pass by reference" requirement but an experienced PHP hacker might remove the line from the code because its not needed. 

Maybe the bottom line is to write even more "verbose" examples?

Gabriel you don't need to use eval() to solve this issue.. I'll try to explain by making your first example work the way you're thinking.  I changed some variable names for convenience but it's the same example.

$my = new mysqli('localhost', 'test', 'test', 'testdb');

$stmt = $my->prepare('INSERT INTO `car` (`brand`, `brand_id`,
`car_type`) VALUES (?, ?, ?)');

$params = array('sss', 'GMC', 1, 'SUV');

//Okay I'll assume that the above is what I have to work with.
$types = $params[0];
unset($param[0]);
$i = 0;
foreach ($params as $param) {
   $bind_name = 'bind' . $i;
   $$bind_name = $param;
   $bind_names[] = &$$bind_name;
}
$bind_params[] = $types;
$bind_params[] = array_merge($bind_params, $bind_names)
//Added code ends here.

$return = call_user_func_array(array($stmt, 'bind_param'), $bind_params);

var_dump($return);

$stmt->execute();

echo $stmt->errno, ':', $stmt->error;

So now you got yourself a working code.  With the same method of binding, you can make yourself the ultimate lazy query function that handles this situation:
$params = array('sss', 'GMC', 1, 'SUV');

query('INSERT INTO `car` (`brand`, `brand_id`,
`car_type`) VALUES (?, ?, ?)', $params);

or this is my preference but it doesn't handle BLOB types:

query('INSERT INTO `car` (`brand`, `brand_id`,
`car_type`) VALUES (?, ?, ?)', $brand, $brand_id, $car_type);

Anyways my point is I do agree with this logic though the doc explanation "call_user_func_array" is MISLEADING.  I couldn't figure it out until I saw uw.php.net's examples.  The whole binding scenario is pretty tough and inflexible.  Still needs to be looked over by an expert =)

It's been a long time I haven't seen dynamic variables ($$var) in PHP code. I consider that such language constructs are what make PHP code sometime very unreadable, and creates very hard-to-find bugs. Nice workaround though :-)

And you're right, the binding scenario is totally illogical and inflexible. I think the normal scenario is creating the variables (or an array of constant variables such as "array('abc', '3, 'test')", and then binding these with the prepared statement, but not like in the bind_param doc example which does a binding with auto-created variables, then assigns them some data. Besides, using undefined variables in a function call causes PHP  to throw a Notice in E_ALL error mode, doesn't it? (Maybe it's different with references, but undocumented)

Note this is not the first time I see some very strange PHP behavior when using references (PHP-like pointers), not to mention how hard it is to do debugging with them.

Or maybe I'm completely wrong in the way I write my own PHP code logic?

Anyway, I'm a bit out of this bug report's context. We still have a bug in the way call_user_func_array returns functions passing variables by reference.

This bug has been fixed in CVS.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
 
Thank you for the report, and for helping us make PHP better.

As Ulf (uw) said above: mysqli_stmt_bind_param() expects the parameters to be references.It worked (more or less) by accident in previous versions. But Dmitry now added a Warning so it won't fail silently; with a current snapshot you'll get a error like "Warning: Parameter 1 to mysqli_stmt::bind_param() expected to be a reference, value give in ...". see eyitsjunk at gmail dot com's comment to see how you can set the references right.

A fix for the Zend Framework has been proposed: http://framework.zend.com/issues/browse/ZF-2529