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<H1>PHP3 Frequently Asked Questions</H1>
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<P>This is a list of Frequently Asked Questions about PHP3 and
their answers. If you have suggestions or additions, send them to
<CODE>php3@php.il.eu.org</CODE>.
<HR>
<H2>General Information</H2>
<H3>What is PHP3?</H3>
<P>From the <A href="http://www.php.net/manual/manual.html">manual</A>:
<BLOCKQUOTE>
<P>Professional Home Pages Version 3.0 is an HTML-embedded scripting
language. Much of its syntax is borrowed from C, Java and Perl with a
couple of unique PHP-specific features thrown in. The goal of the language
is to allow web developers to write dynamically generated pages quickly.
</BLOCKQUOTE>
<H3>What is its relation to PHP/FI?</H3>
PHP3 is the successor to PHP/FI 2.0.
<H3>What are the differences between PHP3 and PHP/FI 2.0?</H3>
<P>For a complete list of the changes, read the <A href="changes.php3">CHANGES</A>
file included in the PHP3 distribution. Some highlights:
<UL>
<LI>All-new parser.
<LI>Persistent database connections.
</UL>
<H3>I heard it's possible to access Microsoft SQL Server from PHP3. How?</H3>
<P>On Windows 95/NT machines, you can simply use the included ODBC support
and the correct ODBC driver.
<P>On Unix machines, you can use the Sybase-CT driver to access Microsoft
SQL Servers because they are (at least mostly) protocol-compatible. Sybase
has made a <a href="/extra/ctlib-linux-elf.tar.gz">free version of the necessary libraries for Linux systems</a>.
For other Unix operating systems, you need to contact Sybase for the correct
libraries (which cost money).
<H3>Can I access Microsoft Access databases?</H3>
<P>Yes. You already have all the tools you need if you are running
entirely under Windows 95 or NT, where you can use ODBC and Microsoft's
ODBC drivers for Microsoft Access databases. From other platforms, you
would need to have a server running Windows NT (or possibly Windows 95)
which you connected to using ODBC drivers from your other platform and
<A href="http://www.openlinksw.com/">OpenLink Software's ODBC Agent</A>
software, which runs US$4,000.
<P>Some better alternatives are to use an SQL server that has Windows ODBC
drivers and use that to store the data, which you can then access from
Microsoft Access (using ODBC) and PHP3 (using the built-in drivers), or
to use an intermediary file format that Access and PHP3 both understand,
such as flat-files or dBase databases.
<H3>I saw PHP3 offers persistent database connections. What does that mean?</H3>
<p>Persistent connections are SQL links that do not close when the
execution of your script ends. When a persistent connection is requested,
PHP checks if there's already an identical persistent connection (that
remained open from earlier) - and if it exists, it uses it. If it does
not exist, it creates the link. An 'identical' connection is a connection
that was opened to the same host, with the same username and the same
password (where applicable).
<p>People who aren't thoroughly familiar with the way Web servers work and
distribute the load may mistake persistent connects for what they're not.
In particular, they do NOT give you an ability to open 'user sessions' on
the same SQL link, they do NOT give you an ability to build up a transaction
efficently, and they don't do a whole lot of other things. In fact, to be
extremely clear about the subject, persistent connections don't give you ANY
functionality that wasn't possible with their non-persistent brothers.
<p>Why?
<p>This has to do with the way the way Web servers work. We can divide
PHP to three main types. First, PHP in its CGI mode. In CGI mode, there's
no difference between persistent and non persistent connects. The reason is
simple - a CGI binary terminates as soon as the execution of your script ends.
Obviously, when it dies, any resource it may have 'owned', including any type
of SQL link, dies with it (in practice PHP is nicer and properly closes the
SQL link right before it dies, but even if it didn't, the link wouldn't have
been reusable).
<p>The second way of running PHP is as a plugin for a *multithreaded* server.
Currently, this is only theoratical - Shane has a thread safe ISAPI module
in the works, and NSAPI/Win32 will probably follow soon after the ISAPI one
works right. Multithreaded servers are a bit different in what they enable
developers to do, even though as far as I can tell right now, PHP's behavior
would be identical to the one of *multiprocess* servers. See below.
<p>The last, and most popular way of running PHP is as a plugin to the
multiprocess server - apache. A quick guide to the way apache (usually)
works - apache has one 'parent' process, that doesn't answer to requests.
Its job is to coordinate between its children. The children, which are
spawned by the parent, are the processes that answer to HTTP requests. The
load of the requests is divided among all of the children. That is, two
subsequent hits on the same page are likely to be handled by TWO DIFFERENT
PROCESSES. This is the key issue here. There are plenty of processes that
make the 'Web server', and the load is distributed among them.
<p>What does that have to do with persistent connections? Everything. That
explains why there's no added functionality in persistent connections. When
you open a persistent connection, you can't do something like beginning a
transaction, and hope that the next time the user submits a page you'd just
continue the transaction. You can't lock tables and hope that the next hit
by the user will unlock the tables. The two requests are most likely to be
handled by two different processes!
<p>If persistent connections don't have any added functionality, what are
they good for?
<p>The answer here is extremely simple - efficiency. Persistent connections
are good if the overhead to create a link to your SQL server is high.
Whether or not this overhead is really high depends on many factors. Like,
what kind of database it is, whether or not it sits on the same computer on
which your web server sits, how loaded the machine the SQL server sits on is
and so forth. The bottom line is that IF that connection overhead is high,
persistent connects help you. They simply connect only once for the entire
lifespan of the httpd child, instead of once per hit that child processes.
Make sure you understand - this means that for every child that opened a
persistent connection will have its own open persistent connection to the
server. That is, if you had 20 different httpd processes that ran a script
that included a pconnect(), you'd have 20 different connections to the SQL
server, one from each child.
<p>An important summary. pconnects were designed to have 1::1 mapping to
regular connects. That means that you should ALWAYS be able to replace
persistent connect with a non-persistent connect, and it won't change the
way the script behaves. It MAY and probably will change the efficiency of
the script, but not its behavior!
<H3>Is there a PHP3 mailing list?</H3>
<P>Of course! To subscribe, send mail to
<CODE>php3-subscribe@php.il.eu.org</CODE>. You don't need to include
anything special in the subject or body of the message.
<P>To unsubscribe, send mail to
<CODE>php3-unsubscribe@php.il.eu.org</CODE>.
<H3>Help! I can't seem to subscribe to the mailing list!</H3>
<H3>Help! I can't seem to unsubscribe from the mailing list!</H3>
<P>If you have problems subscribing to or unsubscribing from the PHP3
mailng list, it may be because the mailing list software can't figure
out the correct mailing address to use. If your email address was
<CODE>joeblow@example.com</CODE>, you can send your subscription request
to <CODE>php3-subscribe-joeblow=example.com@php.il.eu.org</CODE>,
or your unsubscription request to
<CODE>php3-unsubscribe-joeblow=example.com@php.il.eu.org</CODE>.
<H3>Is there an archive of the mailing list anywhere?</H3>
<P>Yes, it's located at <A
href="http://www.tryc.on.ca/php3.html">http://www.tryc.on.ca/php3.html</A>.
<HR>
<H2>Obtaining PHP3</H2>
<H3>Where can I obtain PHP3?</H3>
<P>You can download PHP3 from any of the members of the
PHP3 network of sites. These can be found at <A
href="http://www.php.net/">http://www.php.net/</A>.
You can also use anonymous CVS to get the absolute latest
version of the source. For more information, go to <A
href="http://www.lerdorf.on.ca/php3.cgi">http://www.lerdorf.on.ca/php3.cgi</A>.
<H3>Where can I get libraries needed to compile some of the optional
PHP3 extensions?</H3>
<P>Note: Those marked with * are not thread-safe libraries, and should
not be used with PHP3 as a server module in the multi-threaded Windows web
servers (IIS, Netscape). This does not matter in Unix environments, yet.
<UL>
<LI>LDAP (unix): <A href="ftp://terminator.rs.itd.umich.edu/ldap/ldap-3.3.tar.Z">ftp://terminator.rs.itd.umich.edu/ldap/ldap-3.3.tar.Z</A>
<LI>LDAP* (win): <A href="ftp://terminator.rs.itd.umich.edu/ldap/windows/winldap.zip">ftp://terminator.rs.itd.umich.edu/ldap/windows/winldap.zip</A><br>
There is also a free LDAP server at: <A href="ftp://ftp.critical-angle.com/pub/cai/slapd/">ftp://ftp.critical-angle.com/pub/cai/slapd/</A>.
<LI>Berkeley DB2 (Unix/Win): <A href="http://www.sleepycat.com/">http://www.sleepycat.com/</A>
<LI>SNMP (Unix): <A href="http://www.ece.ucdavis.edu/ucd-snmp/">http://www.ece.ucdavis.edu/ucd-snmp/</A> (Note: PHP3 uses the native SNMP interface in Windows.)
<LI>GD* (Unix/Win): <A href="http://www.boutell.com/gd/#buildgd">http://www.boutell.com/gd/#buildgd</A>
<LI>mSQL (Unix): <A href="http://www.hughes.com.au/">http://www.hughes.com.au/</A>
<LI>mSQL* (Win) : <A HREF="http://blnet.com/msqlpc/">MSQL PC Home Page</a>
<LI>MySQL (Unix): <A href="http://www.tcx.se/">http://www.tcx.se/</A>
<LI>IMAP* (Win/Unix): <A HREF="ftp://ftp.cac.washington.edu/imap/imap-4.1.BETA.tar.Z">ftp://ftp.cac.washington.edu/imap/imap-4.1.BETA.tar.Z</a>
<LI>Sybase-CT (Linux, libc5): <a href="/extra/ctlib-linux-elf.tar.gz">Available locally</a>
</UL>
<H3>How do I get these libraries to work?</H3>
<P>You will need to follow instructions provided with the library. Some of
these libraries are detected automatically when you run the 'configure'
script of PHP3 (such as the GD library), and others you will have to
enable using '--with-EXTENSION' options to 'configure'. Run 'configure
--help' for a listing of these.
<H3>Are pre-compiled binary versions available?</H3>
<P>Yes, as long as you're looking for binaries for Windows 95 or NT.
They're available in the same place as the source.
<H3>I got the latest version of the PHP3 source code from the CVS
repository on my Windows 95/NT machine, what do I need to compile it?</H3>
<P>First, you will need Microsoft Visual C++ v5 (v4 may
do it also, but we do it with v5), and you will need to <A
href="http://www.php.net/win32/makeparser.zip">download Bison and
Flex</A>. You will need to put Bison and Flex somewhere in your path,
or add their location to your path. Then run the batch file 'makeparser'
before compiling with MSVC. You also may need to edit some settings
in the project settings. You should be familier enough with MSVC to
know what to do ;).
<HR>
<H2>Installation</H2>
<P>To install PHP3, follow the instructions in the INSTALL file located
in the distribution. Windows 95 and NT users should also read the
README.WIN32 file.
<H3>Common Problems</H3>
<DL>
<DT><B>
I got the latest version of PHP3 using the anonymous CVS service,
but there's no configure script!
</B></DT>
<DD>
You have to have the GNU autoconf package installed so you can
generate the configure script from configure.in. Just run
<CODE>autoconf</CODE> in the top-level directory after getting
the sources from the CVS server. (Also, unless you run configure
with the <CODE>--enable-maintainer-mode</CODE> option, the
configure script will not automatically get rebuilt when the
configure.in file is updated, so you should make sure to do that
manually when you notice configure.in has changed. One symptom
of this is finding things like @VARIABLE@ in your Makefile after
configure or config.status is run.
<P>
</DD>
<DT><B>
I'm having problems configuring PHP3 to work with Apache. It says
it can't find httpd.h, but it's right where I said it is!
</B></DT>
<DD>
You need to tell the configure/setup script the location of the
<EM>top-level</EM> of your Apache source tree. This means that
you want to specify '<CODE>--with-apache=/path/to/apache</CODE>'
and <EM>not</EM> '<CODE>--with-apache=/path/to/apache/src</CODE>'.
<P>
</DD>
<DT><B>
When I run configure, it says that it can't find the include files or
library for gdbm (or some other package)!
</B></DT>
<DD>
You can make the configure script looks for header files and libraries
in non-standard locations by specifying additional flags to pass to
the C compiler, such as:
<PRE>
CFLAGS=-I/path/to/include LDFLAGS=-L/path/to/library ./configure
</PRE>
If you're using a csh-variant for your login shell (why?), it would be:
<PRE>
env CFLAGS=-I/path/to/include LDFLAGS=-L/path/to/library ./configure
</PRE>
<P>
</DD>
<DT><B>
When it is compiling the file language-parser.tab.c, it gives me errors
that say 'yytname undeclared'.
</B></DT>
<DD>
You need to update your version of Bison. You can find the latest version
at <A href="ftp://prep.ai.mit.edu/pub/gnu/">ftp://prep.ai.mit.edu/pub/gnu/</A>.
<P>
</DD>
<DT><B>
When I run 'make', it seems to run fine but then fails when it
tries to link the final application complaining that it can't find
some files.
</B></DT>
<DD>
Some old versions of make that don't correctly put the compiled
versions of the files in the functions directory into that same
directory. Try running "<CODE>cp *.o functions</CODE>" and then
re-running 'make' to see if that helps. If it does, you should really
upgrade to a recent version of GNU make.
<P>
</DD>
<DT><B>
When linking PHP3, it complains about a number of undefined references.
</B></DT>
<DD>
Take a look at the link line and make sure that all of the appropriate
libraries are being included at the end. Common ones that you might have
missed are '-ldl' and any libraries required for any database support
you included.
<P>
If you're linking with Apache 1.2.x, did you remember to add the
appropriate information to the EXTRA_LIBS line of the Configuration
file and re-rerun Apache's Configure script? See the INSTALL file that
comes with the distribution for more information.
<P>
Some people have also reported that they had to add '-ldl' immediately
following 'libphp3.a' when linking with Apache.
<P>
</DD>
<DT><B>
I can't figure out how to build PHP3 with Apache 1.3.
</B></DT>
<DD>
<P>This is actually quite easy. Follow these steps carefully:
<UL>
<LI>Grab the latest Apache 1.3 distribution from <A href="http://www.apache.org/dist/">www.apache.org</A>.
<LI>Ungzip and untar it somewhere, for example /usr/local/src/apache_1.3b3.
<LI>Compile PHP3 by first running ./configure --with-apache=/<i>&lt;path&gt;</i>/apache_1.3b3 (substitute <i>&lt;path&gt;</i> for the actual path to your apache_1.3b3 directory.
<LI>Type 'make' followed by 'make install' to build PHP3 and copy the
necessary files to the Apache distribution tree.
<LI>Change directories into to your /<i>&lt;path&gt;</i>/apache_1.3b3/src directory and edit the <i>Configuration</i> file. At the end of the file, add: <tt>AddModule modules/extra/mod_php3.o</tt>.
<LI>Type: './Configure' followed by 'make'.
<LI>You should now have a PHP3-enabled httpd binary!
</UL>
<P>
</DD>
</DL>
<HR>
<H2>Using PHP3</H2>
<H3>Common Problems</H3>
<DL>
<DT><b>
I installed PHP3, but every time I load a document, I get the
message 'Document Contains No Data'! What's going on here?
</b></DT>
<DD>
This probably means that PHP3 is having some sort of problem
and is core-dumping. Look in your server error log to see if
this is the case, and then try to reproduce the problem with
a small test case. If you know how to use 'gdb', it is very
helpful when you can provide a backtrace with your bug report
to help the developers pinpoint the problem.
<P>
If your script uses the regular expression functions (<CODE>ereg()</CODE>
and friends), you should make sure that you compiled PHP3 and
Apache with the same regular expression package. (This should
happen automatically with PHP3 and Apache 1.3.)
<P>
</DD>
<DT><B>
I'm trying to access one of the standard CGI variables (such
as $DOCUMENT_ROOT or $HTTP_REFERER) in a user-defined function,
and it can't seem to find it. What's wrong?
</B></DT>
<DD>
Environment variables are now normal global variables, so you must
either declare them as global variables in your function (by using
"<CODE>global $DOCUMENT_ROOT;</CODE>", for example) or by using
the global variable array (ie, "<CODE>$GLOBALS["DOCUMENT_ROOT"]</CODE>".
<P>
</DD>
</DL>
<H3>I think I found a bug! Who should I tell?</H3>
<P>You should go to the PHP Bug Database and make sure
the bug isn't a known bug. If you don't see it in the database,
use the reporting form to report the bug. It is important to use
the bug database as opposed to just sending an email to one
of the mailing lists because by using the database the bug will
get an id assigned and it will then be possible for you to go back
later and check on the status of the bug. The bug database
can be found at <a href="http://ca.php.net/bugs.php3">http://ca.php.net/bugs.php3</a>.
<HR>
<H2>Migrating from PHP/FI 2.0</H2>
<H3>Common Problems</H3>
<DL>
<DT><B>
I converted my script from PHP/FI 2.0 to PHP3 syntax, but now it just
hangs! When I looked at the processes running on my server, there was
one process that was chewing up all of the CPU cycles!
</B></DT>
<DD>
You probably missed the semi-colon on a <CODE>while
(condition);</CODE> statement. This will cause PHP3 to spin out of
control because it is simply executing an empty body for your while
loop! Change the semi-colon to a colon and it should work correctly.
<P>
</DD>
<DT><B>
My user-functions don't work any more! I get a "Parse error (expecting '('"
on the first line of the function.
</B></DT>
<DD>
PHP3's function declaration now resembles C function declarations, so
your function should look like:
<PRE>
function printsum($a, $b) {
echo $a + $b;
}
</PRE>
<P>You can also use old-style function declarations by use the
'old_function' designation, like so:
<PRE>
old_function printsum $a, $b (
echo $a + $b;
);
</PRE>
<P>
</DD>
</DL>
<HR>
<H2>Credits</H2>
<P>This FAQ was originally written by Jim Winstead. It is currently
maintained by the PHP Development Team.
<P>
<SMALL>
<CODE>$Id$</CODE>
</SMALL>
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