Description:
------------
Originally tested with PHP 5.3.3.7+squeeze8 with Suhosin-Patch (cli) (built: Feb 
10 2012 13:05:56) from Debian repository, confirmed with latest from Debian's 
git repository (announced as 5.4.0).

The sscanf() function, when given variables into which to put its results, is 
documented as returning the number of assigned values: 
http://php.net/manual/en/function.sscanf.php

Usage, however, shows that it can return -1 if the input string does not match 
the pattern - see test script. I'm not sure if this is a documentation error or 
an actual function bug (it seems odd that a prefix match should affect the 
return value), but either way, the disconnect is confusing.

The issue seems to arise from ext/standard/scanf.c lines 687-695 (in latest 
cloned from git), in which different treatment is given to mismatch and 
underflow, and then line 1200 triggers the -1 return in the case of underflow.

My original code (very similar to the test script attached) was using "if 
(sscanf(....)) do_stuff" - had I known about negative returns, a more correct 
line of code would say "if (sscanf(...)>0) do_stuff" instead.


Test script:
---------------
<?php
$_POST = array('foobar1'=>5, 'foobar2'=>7, 'foo'=>'Do some Fooage', 'other'=>42);
foreach ($_POST as $k=>$v)
{
	$ret=sscanf($k,'foobar%d',$id);
	echo "key $k -> id $id, value $v - sscanf returned $ret\n";
}


Expected result:
----------------
According to the documentation, the foobar1 and foobar2 lines should have a 
return value of 1, because $id was assigned to; the other two should have a 
return value of 0.

Actual result:
--------------
The foo line has a return value of -1, unexpected according to the documentation.