This section gathers most common errors you can face,
while writing PHP scripts.
function myfunc($argument) { echo $argument + 10; } $variable = 10; echo "myfunc($variable) = " . myfunc($variable); |
pre ?php echo "This should be the first line."; ? ?php echo "This should show up after the new line above."; ? /pre |
1. I would like to write
a generic PHP script that can handle data coming from
any form. How do I know which POST method variables are
available?
Make sure that the
track_vars feature is enabled in your php.ini file. Since PHP 4.0.3, this
feature is always on. When
track_vars is on, it creates some associative
arrays, the most important here is: $_POST (this used to be called $HTTP_POST_VARS in PHP versions prior 4.1.0). So, to write
a generic script to handle POST method variables you
would need something similar to the following:
foreach ($_POST as $var = $value) { echo "$var = $value br \n"; } |
2. I need to
convert all single-quotes (') to a backslash followed
by a single-quote. How can I do this with a regular
expression?
First off, take a look at the
addslashes() function. It will do exactly what
you want. You should also have a look at the
magic_quotes_gpc directive in your php.ini file.
4. Hey, what happened
to my newlines?
pre ?php echo "This should be the first line."; ? ?php echo "This should show up after the new line above."; ? /pre |
In PHP, the ending for a block of code is either
"? " or "? \n" (where \n means a newline). So in
the example above, the echoed sentences will be on one
line, because PHP omits the newlines after the block
ending. This means that you need to insert an extra
newline after each block of PHP code to make it print
out one newline.
Why does PHP do this? Because when formatting
normal HTML, this usually makes your life easier
because you don't want that newline, but you'd have to
create extremely long lines or otherwise make the raw
page source unreadable to achieve that effect.
5. I get the
message 'Warning: Cannot send session cookie - headers
already sent...' or 'Cannot add header information -
headers already sent...'.
The functions header(),
setcookie() and the session functions need to
add headers to the output stream. But headers can only
be sent before all other content, check if your script
is sending headers after having already sent
content.
The getallheaders() function will do
this if you are running PHP as an Apache module. So,
the following bit of code will show you all the request
headers:
$headers = getallheaders(); foreach ($headers as $name = $content) { echo "headers[$name] = $content br \n"; } |
The security model of IIS is at fault here. This is
a problem common to all CGI programs running under IIS.
A workaround is to create a plain HTML file (not parsed
by PHP) as the entry page into an authenticated
directory. Then use a META tag to redirect to the PHP
page, or have a link to the PHP page. PHP will then
recognize the authentication correctly. With the ISAPI
module, this is not a problem. This should not effect
other NT web servers. For more information, see:
http://support.microsoft.com/support/kb/articles/q160/4/22.asp.
8. My PHP script works
on IE and Lynx, but on Netscape some of my output is
missing. When I do a "View Source" I see the content in
IE but not in Netscape.
Netscape is more strict regarding html tags (such
as tables) then IE. Running your html output through a
html validator, such as
validator.w3.org, might be helpful. For example, a
missing /table might cause this.
Also, both IE and Lynx ignore any NULs (\0) in the HTML stream, Netscape does
not. The best way to check for this is to compile the
command line
version of PHP (also known as the CGI version) and run
your script from the command line. In *nix, pipe it
through od -c and look for any
\0 characters. If you are on
Windows you need to find an editor or some other
program that lets you look at binary files. When
Netscape sees a NUL in a file it will typically not
output anything else on that line whereas both IE and
Lynx will.
You need to turn off the short tags by setting
short_tags to 0 in your
php.ini file, or by using the appropriate Apache
directive. You could even use a File section to
do this selectively.
10. How can I use PHP with FrontPage or some
other HTML editor that insists on moving my code
around?
One of the easiest things to do is to enable using
ASP tags in your PHP code. This allows you to use the
ASP-style % and % code delimiters. Some of the
popular HTML editors handle those more intelligently
(for now). To enable the ASP-style tags, you need to
set the
asp_tags php.ini
variable, or use the appropriate Apache directive.
11. Where can I find a
complete list of pre-set variables available to me, and
why are these not documented in the PHP
documentation?
The best way is to stick a
?php phpinfo(); ? part on a page and load
it up. This will show you all sorts of information
about your PHP setup, including a list of both
environment variables and also special variables set by
your web server. This list can't really be documented
in the PHP documentation because it will change from
one server to another.
12. 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?
Environment variables are normal global variables,
so you must either declare them as global variables in
your function (by using "global
$DOCUMENT_ROOT;", for example) or by using the
global variable array (ie, "$GLOBALS["DOCUMENT_ROOT"]").
注: Since PHP 4.1.0 you can also use the superglobal array $_SERVER which is available in every function. For example, you can now use $_SERVER["DOCUMENT_ROOT"] instead of $DOCUMENT_ROOT.