Note :
this bug doesn't appear when you specify a drive letter.

<?php
mkdir('C:\toto\tata\titi', 0777, true);
?>

When the top directory doesn't exist, the code tries to create directory with empty name because on the previous step we changed first "/" to '\0'.
IMO the simplest way is to check if the first character is 0 and change it to DEFAULT_SLASH.
Not sure how it would work on Windows though.

Index: main/streams/plain_wrapper.c
===================================================================
RCS file: /repository/php-src/main/streams/plain_wrapper.c,v
retrieving revision 1.47
diff -u -p -d -r1.47 plain_wrapper.c
--- main/streams/plain_wrapper.c        20 Jun 2005 15:59:12 -0000      1.47
+++ main/streams/plain_wrapper.c        23 Jun 2005 20:06:47 -0000
@@ -1091,6 +1091,9 @@ static int php_plain_files_mkdir(php_str
                                break;
                        }
                }
+               if (*buf == 0) {
+                       *buf = DEFAULT_SLASH;
+               }
                if (p == buf) {
                        ret = php_mkdir(dir, mode TSRMLS_CC);
                } else if (!(ret = php_mkdir(buf, mode TSRMLS_CC))) {

Please try using this CVS snapshot:

  http://snaps.php.net/php5-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php5-win32-latest.zip

No feedback was provided for this bug for over a week, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".

I have the same bug with PHP 5.0.4 and the given snapshot. But other PHP developpers in my development team does not get the error message while using the same PHP version than mine. The problem occurs on my computer with PHP 5.1 too. 

The only difference I can figure out between those developers and I is that I am still using Windows XP SP1 while they are using Windows XP SP2. Can this be the cause of the bug ?

I have made a little test and I figure out taht giving the full path is not required but that you have to use the backslashes instead of the slashes to make the recursive mkdir work :

<code>
mkdir ('toto/tutu/titi', 0777, true); # FAILS

mkdir ('toto\tutu\titi', 0777, true); # WORKS
</code>

But when not in recursive mode, mkdir works with either slashes or backslashes.

I see this bug on Mac OS X 10.4.5 with PHP 5.1.2.

I've also noticed what I assume is a related problem with creating directories in the current directory. For example, if I run the script below in /tmp, the second (and fifth) mkdir will fail.

<?php
// e.g. running in /tmp                                                         
mkdir('new1', 0700, true);            // works                                        
mkdir('new2/sub', 0700, true);        // fails                                        
mkdir('/tmp/new3/sub', 0700, true);   // works                                    
mkdir('../tmp/new4/sub', 0700, true); // works                                  
mkdir('/new5/sub', 0700, true); // fails, confirming 
                                // the original bug.
?>

Please try using this CVS snapshot:

  http://snaps.php.net/php5.2-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php5.2-win32-latest.zip

No feedback was provided for this bug for over a week, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".

It still does not work with '/' and recursive mode under windows :

<code>
<?php
mkdir ('toto/tutu/titi', 0777, true );
?>
</code>

Warning: mkdir(): No such file or directory in C:\var\downloads\php5.2-win32-latest\test_mkdir.php on line 2

and

<code>
<?php
    mkdir ('C:/var/downloads/php5.2-win32-latest/toto/tutu/titi', 0777, true );
?>
</code>

Using '\' works :

<code>
<?php
    mkdir ('toto\tutu\titi', 0777, true );
?>
</code>

and

<code>
<?php
    mkdir ('C:\var\downloads\php5.2-win32-latest\toto\tutu\titi', 0777, true );
?>
</code>

work fine.

There is no problem in non-recursive mode and the following works fine :

<code>
$path = 'tata/toto/tutu/titi';

$parts = explode( '/', $path );
$trail = '';

foreach( $parts as $part )
{
	$trail .= $part . '/';
	if ( file_exists( $trail ) )
	{
		return false;
	}
	else
	{
		if ( is_dir( dirname( $trail ) ) )
		{
			mkdir ( $trail, 0777 );
		}
	}
}
</code>

This issue is fixed under Windows with PHP 5.2.0

Thank you for your bug report. This issue has already been fixed
in the latest released version of PHP, which you can download at 
http://www.php.net/downloads.php