[RESOLVED] header("Location: filename.php");

ATS16805

i'm trying to get a better understanding of some sample code in a beginners book i'm reading. i'd rather not move on until i figure this out. it's really pretty simple-- just an html form to enter an e-mail address, and then that data is inserted into a table.

although the book claims that this is "not complicated", i'm trying to disect it, and i'm encountering difficulty. from my beginner's perspective, i think there's a lot going on here.

there are several IF / ELSE statments to determine what the output will be. four seperate outputs: one to indicate a successful subscription, one to indicate that the email is already in the db, one to indicate a successful unsubscribe, and one to indicate unsuccessful unsubscribe because the address couldn't be found. there are also allowances for forms submitted w/out any data, so that it will return to the form instead of submitting a NULL value. this is where i'm getting confused because i think the code is malfunctioning, unless i've mistyped something somewhere.

take a look at this, the code (i've paraphrased it) to handle empty form submission:

else if (($_POST[hiddenfield] == "xyz") && ($_POST[radiobutton1] == "buttonvalue1")) {
   //trying to insert record; validate textfield
   if ($_POST[textfield] == "") {
       header("Location: filename.php");
       exit;

if i try this by submitting an empty form, i get the following:
[INDENT]Warning: Cannot modify header information - headers already sent by (output started at c:\program files\apache group\apache\htdocs\webroot\filename.php:19) in c:\program files\apache group\apache\htdocs\webroot\filename.php on line 64
[/INDENT]

any idea what's causing this warning? something i should look for elsewhere in the code?

jonno946

probably the most commonly asked question on this forum.

use the search button 😉

ATS16805

after reading several threads regarding redirects and code causing the "Cannot modify header information" error, i still don't get it.

i mean, before i even did some research, the very nature of the error, and the code (at least in my script) seems to describe what's going on-- that the same header info can't be sent more than once, or is it that it can not be received more than once...

regardless, i don't understand why this book would have laid out the code this way, if it inevitably was going to cause an error. the script is set up to check for $_POST[ab] != [cd] .

since at the point in which that comparison operator is used, the html form embeded in the PHP has not yet been submitted, so $_POST[ab] will have a NULL value every time the page is loaded. this is part of an IF statement in which, when the result of that comparison is returned TRUE, it jumps to the end of the script to an html block in which a variable holding the entire html form is displayed by a single line of PHP w/in that HTML block such that the form is then ECHOed , ready to submit the text fields for reprocessing in this same page.

once the form is submitted, now $POST[ab] == [cd] because of the hidden form value. so, the $POST[ab] != [cd] now returns FALSE and the ELSE IF statements are checked as shown in my first post.

so, i see what's going on... that it is using the same page to display different results depending upon the values of the text field and radio buttons. it doesn't make sense that the book i'm using would contain erroneous code-- at least it doesn't indicate "notice the error produced by line...", know what i mean? no solution is offered, and no error is discussed.

i've searhced php.net for header(), but i didn't find a solution there either. from what i've read here and at php.net's manual, it seems to me that i would practically have to rewrite a lot of the code, or use a separate page.

i'm not discounting the fact that i could be missing something, or that i may have mistyped some code as i copied it from the book, but it still doesn't make sense to me that the code would work otherwise. the header("Location: filename.php"); is used more than once in the script, so it's obviously suppsed to be there as entered. i'm stumped.

when you suggested i do a search, what did you have in mind i use as keywords?

Drakla

no output before your php tags - not even spaces, newlines, tabs - no output in any of the scripts that you include / require if they're before the location, as output causes headers to end and be sent.

LoganK

Jonno - what's on line 36 of showthread.php? Is there something that can be construed as an error or did you just make up a random number to make it look like there's an error with your sig?

ATS16805

Drakla, thank you very much for the explanation.

I'm afraid that, although searching the threads is indeed the best way to start when encountering an obstacle, sometimes the info one needs is more specific to his or her unique situation, and even though something is usually learned during the hunting process, when the hunter is confused about the very thing he is hunting or does not know even what he is hunting, it makes it a bit more difficult.

i would never have thought to look at the output, as Drakla suggested. i was searching for
errors in the logic, going over and over the same != vs == comparision in the IF/ELSE , and coming up w/ nothing.

(maybe i'm still in the dark? but i think i at least know how to approach this error... it's like in the movies when the guy goes in for an apendectomy, and comes out w/ female parts-- i was trying to give my script a similar change!)

ATS16805

okay. i've examined this script over and over, and i can't figure out what is wrong with it.

According to Drakla above, there should be no output before the PHP tags. I'm not exactly sure what that means, but i assume it essentially means that I should see no output before the PHP script runs. i didn't want to include the entire script, but i'm afraid i don't know what else to do. I could be wrong, but the way i see it, this script, which is my modified version of an example in a book which i will cite below is designed to show output not before all the PHP tags, but before some of them. The book is:
Meloni, Julie C. Sams Teach Yourself PHP, MySQL® and Apache All in One. Indianapolis: Sams Publishing, 2003.
There are exercises, workshops and activities at the end of each chapter, and Part V, Basic Projects is a comprehensive list of examples to demonstrate what has been learned up to this point. Chapter 17, Managing a Simple Mailing List, is the script in question. to make the application more practical, I modified the example MySQL table to include two more columns-- one for first name and one for last name. The book has only 2 columns, the not null, auto-incrementing primary Key ID, and the column for the subscribed email addresses. my code is as follows:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>Mailing List Entry Form</TITLE>
<link rel="stylesheet" type="text/css" href="stylesheets/phpstyle.css" media="all" />
</HEAD>
<!-- END HTML CSS BLOCK -->
</html>

<?php
//set up a couple of functions
function doDB() {
	global $conn;

//connect to server and SELECT DATABASE

$conn = mysql_connect("localhost", "myUserName", "MyPassword") 
	or die(mysql_error());
mysql_select_db("testDB",$conn) or die(mysql_error());
}

function emailChecker($email) {
	global $conn, $check_result;

//check that email is not already in list
//THIS FUNCTION IS USED AFTER 
//SUBSCRIBE EMAIL FIELD PASSES DATA
//$check_result STORES ID OF ROW

$check = "select id from subscribers where email = '$email'";
$check_result = mysql_query($check,$conn) or die(mysql_error());
}

//TESTING HIDDEN FORM FIELD:

if ($_POST[op] != "ds") {

//they do, so create FORM BLOCK

$display_block = "
<form method=POST action=\"$_SERVER[PHP_SELF]\">

	<p><strong>Your E-Mail Address:</strong><br>
		<input type=text name=\"email\" size=40 maxlength=150>
		<p>First Name<br>
		<input type=text name=\"firstname\" size=40 maxlength=150>
		<p>Last Name<br>
		<input type=text name=\"lastname\" size=40 maxlength=150>

		<p><strong>Action:</strong><br>
			<input type=radio name=\"action\" value=\"sub\" checked> subscribe
			<input type=radio name=\"action\" value=\"unsub\"> unsubscribe

			<input type=\"hidden\" name=\"op\" value=\"ds\">

				<p><input type=submit name=\"submiit\" value=\"Submit Form\"></p>
					</form>";
//END FORM BLOCK

} else if (($_POST[op] == "ds") && ($_POST[action] == "sub")) {

//IF SUBSCRIBE OPTION CHECKED
//ENSURE FORM 'EMAIL' FIELD PASSED DATA
//IF NO DATA, RELOAD PAGE

if ($_POST[email] == "") {
	header("Location: manage.php");
	exit;
}

//PASSED EMAIL FIELD DATA TEST
//connect to database

doDB();

//check that email is in list

emailChecker($_POST[email]);

//get number of results and do action

if (mysql_num_rows($check_result) < 1) {

	//ADD RECORD

	$sql = "insert into subscribers values
	('', '$_POST[email]', '$_POST[firstname]', '$_POST[lastname]')";
	$result = mysql_query($sql,$conn) or die(mysql_error());
	$display_block = "<p>Thanks for signing up!</p>";
} else {

	//PRINT FAIL MESSAGE
	//IF EMAIL FOUND IN TABLE

$display_block = "<p>You're already subscribed!</p>";
}
} else if (($_POST[op] == "ds") && ($_POST[action] == "unsub")) {

//IF UNSUB CHECKED
//ENSURE FORM 'EMAIL' FIELD PASSED DATA
//IF NOT, THEN RELOAD PAGE

if ($_POST[email] == "") {
	header("Location: manage.php");
	exit;
}

//IF FORM 'EMAIL' PASSED DATA
//connect to database
//COMPARE 'EMAIL' TO TABLE DATA

doDB();

//check that email is in list

emailChecker($_POST[email]);	

//get number of results and do action
//IF 'EMAIL' NOT FOUND
//THEN ROW EQUALS 'NULL' (< 1)

if (mysql_num_rows($check_result) < 1) {

	//print failure message
	//IF 'MAIL' WASN'T FOUND

	$display_block = "<p>Couldn't find your address!</p>
	<p>No action was taken.</p>";
} else {

	//unsubscribe the address
	//'EMAIL' MATCH IN TABLE

	$id = mysql_result($check_result, 0, "id");
	$sql = "delete from subscribers where id = '$id'";
	$result = mysql_query($sql,$conn) or die(mysql_error());
	$display_block = "<p>You're unsubscribed!</p>";
}
}

?>
<HTML>
<HEAD>
<TITLE>Subscribe/Unsubscribe</TITLE>
</HEAD>
<BODY>
<h1>Subscribe/Unsubscribe</h1>
<?php 
echo "$display_block<br>";
echo "information in this function ";
echo "was check_result <span class\"white\">$check_result</span><br>";
echo "the SQL query looked like this <span class=\"dynamic\">$sql</span>";
echo "<br>and the query result was <span class=\"white\">$result</span>";
?>
<p class="html">Click <a href="manage.php">here</a> to return and try again</p>
<p class="html">Click <a href="select_all_subscribers.php">here</a>
to view the table data</p>
</body>
</html>

does it look like it should cause an error? i get the error when i try to submit an empty field. according to the book, the way i understand it is, if i submit an empty field (or fields in my case), the page is supposed to reload so that i can try again.

what do you suggest i do?

LoganK

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>Mailing List Entry Form</TITLE>
<link rel="stylesheet" type="text/css" href="stylesheets/phpstyle.css" media="all" />
</HEAD>

</html>

You call that no output before your PHP tag!??!!?!?

ATS16805

dude, you are a genius.

funny thing is, the html bit at the top, w/ the title and all that was a "new" addition as i was tired of looking at a white screen. however, i have changed a few things since the original error when i started this thread... like fixing the extension on php.ini (the default in my version was php.dist). although many other functions apparently worked, this one did not.

since i wasn't able to extrapolate completely what hid between the lines, i didn't realize that the head there was in fact "output". seems as though i tested the script at the most inopportune times for arriving at a solution... when i first tried, it didn't work... then i left it for a while, tooled w/ some other things, like mail(), fixed my php.ini file, then went on to play w/ some CSS stuff, added my stylesheet ref in the head, and the rest is history.

i removed the bit that i call no output, and the script does in fact work now. good job!

LoganK

Glad you finally got it resolved 🙂

Now please mark the thread resolved ("Thread Tools" -> "Mark Thread Resolved")!

thorpe

ATS, i like your style. i like a newbie who would rather get stuck and actually learn something rather than ignore there problem and hope a) it was a one off and wont happen again. or worst still b) asks for a solution with no intention of finding out why the solution worked.

good to see this is sorted and you actually understand what the problem was. come back as soon as you get more questions.

ATS16805

it's still a bit over my head, to be honest. I'd like to get myself into a similar situation, or be presented w/ a similar exercise to better understand. I mean, I get what Logan and Drakla are telling me, but it's kind of a one-dimensional problem/ solution... i'd like to get in there, and piece by piece disect it till finally i change the variable (not PHP variable, but problem variable) which makes it either work or crash. i think only then will i really be able to "see" it.

The whole != thing for checking if the form had been submitted, seems very "oh, well of course it works", yet, it's still difficult for me to see "why" it works so perfectly. As you might have noticed from my output block at the bottom, i fixed it so i could see the inner functions.

why is the $check_result variable (the mysql_query) always Resource id #2? i think that's the most important function in this script, and i don't quite get it.