CSS vs "Cannot modify header information" Err

ATS16805

I've encountered this issue before. Logan and Drakla were kind enough to point me in the right direction so as to avoid my error, resulting in my desired script action. However, I hastily marked the thread "resolved", and later found that i needed some more info... but i don't think anyone ever saw that. so, now that i've encountered it again, i hope that i can figure out once and for all how to avoid this error.

take a look at my code. this is from a project example in the book:

Meloni, Julie C.(2003)Teach Yourself PHP, MySQL® and Apache All in OneIndianapolis, IN, USA: Sams Publishing

However, I have modified some of the code, only in the reference to include my stylesheet

I guess my question is simple, really. I need to know how to code in my CSS markup w/out having output before my PHP tags. How is this accomplished? i tried by putting it inside the PHP code as in using print below taken from my erroneous code-- my only modification is at lines 5 and 8:

<?php
if ($_POST[op] != "send") {
	//haven't seen the form, so show it
	print "
        <!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01//EN\"
		\"http://www.w3.org/TR/html4/strict.dtd\">
	<HTML>
		<HEAD>		
		<link rel=\"stylesheet\" type=\"text/css\" href=\"stylesheets/phpstyle.css\" media=\"all\" />
		<TITLE>Send a Newsletter</TITLE>
		</HEAD>
		<BODY>
		<h1>Send a Newsletter</h1>
		<form method=\"post\" action=\"$_SERVER[PHP_SELF]\">
		<p><strong>Subject:</strong><br>
		<input type=\"text\" name=\"subject\" size=30></p>
		<p><strong>Mail Body:</strong><br>
		<textarea name=\"message\" cols=50 rows=10 wrap=virtual></textarea>
		<input type=\"hidden\" name=\"op\" value=\"send\">
		<p><input type=\"submit\" name=\"submit\" value=\"Send It\"></p>
		</FORM>
		</BODY>
		</HTML>";

} else if ($_POST[op] == "send") {
	//want to send form, so check for required fields
	if (($_POST[subject] =="") || ($_POST[message] == "")) {
		header("Location: sendmymail.php");
		exit;
	}

again, i realize that i need to not have output before my PHP tags, as instructed by Drakla and Logan, but i don't understand why adding the stylesheet info after <HEAD> and before <TITLE> makes it any different from the author's code, although, w/out my CSS lines in there, i do NOT get an error.

I can hit "submit" once w/ my CSS in the code, but the second try of submitting a blank form results in the Header error. The author's code however, i can hit submit as many times until i get tired of it, and there is still no error.

please help me to understand this more clearly. thank you!

halojoy

hello

first lets see what some PHP Code
colors might reveal about your script

real handy and sometimes we can see where things go wrong
just by colors, stright at a quick glance

<?php

if ($_POST[op] != "send") {
//haven't seen the form, so show it
print "
        <!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01//EN\"
\"http://www.w3.org/TR/html4/strict.dtd\">
<HTML>
<HEAD>
<link rel=\"stylesheet\" type=\"text/css\" href=\"stylesheets/phpstyle.css\" media=\"all\" />
<TITLE>Send a Newsletter</TITLE>
</HEAD>
<BODY>
<h1>Send a Newsletter</h1>
<form method=\"post\" action=\"{$_SERVER[ 'PHP_SELF' ]}\">
<p><strong>Subject:</strong><br>
<input type=\"text\" name=\"subject\" size=30></p>
<p><strong>Mail Body:</strong><br>
<textarea name=\"message\" cols=50 rows=10 wrap=virtual></textarea>
<input type=\"hidden\" name=\"op\" value=\"send\">
<p><input type=\"submit\" name=\"submit\" value=\"Send It\"></p>
</FORM>
</BODY>
</HTML>";

} else if ($_POST[op] == "send") {
//want to send form, so check for required fields
if (($_POST[subject] =="") || ($_POST[message] == "")) {
header("Location: sendmymail.php");
exit;
}

?>

lets keep it according to php standard recommended coding style

I changed this line, putting single quotes around phpself
and added { } brackets, just in case

echo "<form method=\"post\" action=\"{$_SERVER[ 'PHP_SELF' ]}\">";

your code looks alright
and does not give me a clue why you get
headers already sent

/halojoy

simple and easy coding in php

🙂 🙂

halojoy

maybe we can try
alter the order of
result of IF test:

<?php

if ( $_POST[ 'op' ] == "send" ) { 

//want to send form, so check for required fields 

if (  $_POST[ 'subject' ] ==""   ||  $_POST[ 'message' ] == ""   ) { 
   // do something like fill in subject message
    $error = "empty form field<br>
                go back, press your back button";
    echo $error;
    exit;
    }

   else {
   // was okay with subject and message
    header("Location: sendmymail.php"); 
    exit; 
    }

}

else {

// not send
// haven't seen the form, so show it 

print " 
        <!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01//EN\" 
\"http://www.w3.org/TR/html4/strict.dtd\"> 
<HTML> 
<HEAD> 
<link rel=\"stylesheet\" type=\"text/css\" href=\"stylesheets/phpstyle.css\" media=\"all\" /> 
<TITLE>Send a Newsletter</TITLE> 
</HEAD> 
<BODY> 
<h1>Send a Newsletter</h1> 
<form method=\"post\" action=\"{$_SERVER[ 'PHP_SELF' ]}\"> 
<p><strong>Subject:</strong><br> 
<input type=\"text\" name=\"subject\" size=30></p> 
<p><strong>Mail Body:</strong><br> 
<textarea name=\"message\" cols=50 rows=10 wrap=virtual></textarea> 
<input type=\"hidden\" name=\"op\" value=\"send\"> 
<p><input type=\"submit\" name=\"submit\" value=\"Send It\"></p> 
</FORM> 
</BODY> 
</HTML>"; 

exit; // an End Script wait for submit, just for make sure stop here
}

?>

one problem only,
those $_POSTED variables
will be lost, when you send user to next
sendmail page.

You better include sendmail in this page instead
and send user somewhere After sendmail is completed.

include this instead of
header location line:

$subject = $_POST [ 'subject' ];
$message = $_POST [ 'message' ];

mail ( "maymail@hotmai.com", $subject, $message );

echo "your mail was sent<br>
now, go back to index";

exit;

thorpe

the problem is quite simple. you cannot send any output to the browser before calling the header() function. this includes anything echo'ed by php, html that is outside of php, whitespace.... anything.

you might want to look at output buffering as a workaround.

besides that.... the logic of this code is out of whack.

} else if ($_POST[op] == "send") {
	//want to send form, so check for required fields
	if (($_POST[subject] =="") || ($_POST[message] == "")) {
		header("Location: sendmymail.php");
		exit;
	}

doing a redirect to sendmymail.php here after the form has been submitted will not forward the posted variables to sendmymail.php. they will be lost.

ATS16805

i should give credit where credit is due, and show you the complete script for the "sendmymail.php" example from the book, which i cited above. i sense that there my be some confusion because i didn't provide specific enough data regarding the script.

please note that this script is the complete contents of what i named "sendmymail_bookcopy.php", so as to separate the book code from my own modified script. so, no longer is sendmymail.php called in the script, it is now sendmymail_bookcopy.php

<?php
if ($_POST[op] != "send") {
   //haven't seen the form, so show it
   print "
   <HTML>
    <HEAD>
    <TITLE>Send a Newsletter</TITLE>
    </HEAD>
    <BODY>
    <h1>Send a Newsletter</h1>
   <form method=\"post\" action=\"$_SERVER[PHP_SELF]\">
    <P><strong>Subject:</strong><br>
    <input type=\"text\" name=\"subject\" size=30></p>
    <P><strong>Mail Body:</strong><br>
    <textarea name=\"message\" cols=50 rows=10 wrap=virtual></textarea>
   <input type=\"hidden\" name=\"op\" value=\"send\">
   <p><input type=\"submit\" name=\"submit\" value=\"Send It\"></p>
   </FORM>
    </BODY>
    </HTML>";

} else if ($_POST[op] == "send") {
    //want to send form, so check for required fields
    if (($_POST[subject] =="") || ($_POST[message] == "")) {
       header("Location: sendmymail_bookcopy.php");
       exit;
   }

   //connect to database
   $conn = mysql_connect("localhost", "myId", "myPass")
        or die(mysql_error());
   mysql_select_db("testDB",$conn)  or die(mysql_error());

   //get emails from subscribers2 list
   $sql = "select email from subscribers2";
   $result = mysql_query($sql,$conn) or die(mysql_error());

   //create a From: mailheader
   $headers = "From: Your Mailing List <you@yourdomain.com>";

   //loop through results and send mail
   while ($row = mysql_fetch_array($result)) {
       set_time_limit(0);
       $email = $row['email'];
       mail("$email", stripslashes($_POST[subject]),
            stripslashes($_POST[message]), $headers);
       print "newsletter sent to: $email<br>";
   }
}
?>

does placing it w/in the context of the rest of the script help? i thought since i showed the logic of the part that was giving me my error, that perhaps the rest of the script wasn't necessary to post. my apologies. (is it generaly good or bad etiquette to copy/past large amounts of code into posts in this forum? i only submitted the snippet earlier because i thought it better to keep it short and sweet.)

Thorpe, i'm concerned by your comment about the logic being out of whack-- after all, this is the book where i've learned 90% of my php knowledge. does this contextual placement seem to make more sense logically, or do you still feel the same? (that's not supposed to sound irreverent by the way)

Drakla

Php books being accurate - hah! The Luke and Laura Welling: Php & Mysql Web Development (2nd Edition) is a fekkin shambles from start to end.

Posting chunks of code is ok unless it's stupidly big, in that case use an attachment - I would recommend against using text talk, though, as this is a forum, not a 64 x 32 pixel screen. There might even be something in the FAQ discouraging it.

In that example it's using $POST[op] which should be $POST['op'], as I don't see any constant defined name op. The redirect makes sense if the script is itself called sendmymail_bookcopy.php, so it'll redirect to itself when fields aren't filled out, but that should really get caught in the first if block. Also there's no need to put quotes around "$email" in the mail function. Plus you're stripslashing? Why? Out of habit, or just forming a bad one? It only needs applying if magic quotes are set to on - checkied with [man]get_magic_quotes_gpc[/man]

This might help - it saves me the occasional screaming session - http://www.webmasterstop.com/63.html

halojoy

hehe

one thing puzzles me here
these last 3-4 posts
comes with good pieces advice

Now,
what was wrong with my suggestions EARLIER POSTED in this thread

Putting it together in genuine halojoy code
it adds up to this script:

<?php 

if ( $_POST[ 'op' ] == "send" ) {  

//want to send form, so check for required fields 

if (  $_POST[ 'subject' ] ==""   ||  $_POST[ 'message' ] == ""   ) {  
   // do something like fill in subject message 
    $error = "empty form field<br> 
                go back, press your back button"; 
    echo $error; 
    exit; 
    } 

   else { 
/*
 was okay with subject and message 
 header("Location: sendmymail.php");  

 exit;  

-------------------------------
one problem only, 
those $_POSTED variables 
will be lost, when you send user to next 
sendmail page. 

You better include sendmail in this page instead 
and send user somewhere After sendmail is completed. 

include this instead of 
header location line:
*/

  $subject = $_POST[ 'subject' ]; 
  $message = $_POST[ 'message' ]; 

  mail ( "mymail@hotmail.com", $subject, $message, $headers ); 

  echo "your mail was sent<br> 
  now, go back to index"; 

  exit; 

} 

else { 

// not send 
// haven't seen the form, so show it 

print "  

        <!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01//EN\"  

\"http://www.w3.org/TR/html4/strict.dtd\"> 
<HTML> 
<HEAD> 
<link rel=\"stylesheet\" type=\"text/css\" href=\"stylesheets/phpstyle.css\" media=\"all\" /> 
<TITLE>Send a Newsletter</TITLE> 
</HEAD> 
<BODY> 
<h1>Send a Newsletter</h1> 
<form method=\"post\" action=\"{$_SERVER[ 'PHP_SELF' ]}\"> 
<p><strong>Subject:</strong><br> 
<input type=\"text\" name=\"subject\" size=30></p> 
<p><strong>Mail Body:</strong><br> 
<textarea name=\"message\" cols=50 rows=10 wrap=virtual></textarea> 
<input type=\"hidden\" name=\"op\" value=\"send\"> 
<p><input type=\"submit\" name=\"submit\" value=\"Send It\"></p> 
</FORM> 
</BODY> 
</HTML>";  

exit; // an End Script wait for submit, just for make sure stop here 
} 

?>

[right]seems like

halojoy
is one step ahead

again
and
again
and

😃 😃 [/right]

ATS16805

thank you both for your input. i have been spending so much time reading responses, and trying new things, not to mention working on another not-so-complicated fairly static development project, i haven't got to apply anything from this thread yet. but i will when i'm ready to revisit this problem, so thank you halojoy. i didn't purposefully disregard your advice-- i simply haven't got to it yet, and the reason i posted the full script was to make it clear that this wasn't necessarily a question of me learning something about the logic being "out of whack", but it was a question of whether i was receiving proper guidance from this book-- at least that's the way i saw it.

thanks again. Drakla, i appreciate you taking the time to add your commentary and suggested fixes. it helps.

edit:
oh, and the stripslashes thing... i wondered about that myself. when i looked it up ( i think the same URL you've provided) it didn't make much sense to me as to why i was included, other than for simply exposing the reader to the magic quotes thing. who knows. i didn't see a reason for it, thats for sure. although, i have since used it in my own mail() function because i saw it there, and thought it a required part of the mail() syntax. i'm guessing i don't need it then?

ATS16805

This is MADDENING!

I think what i'm going to have to do is accept the fact that the book example produces an error-- because it does! i visited this problem for the final time. i copied the code from the book line for line, changed the appropriate MySQL user info, and it does NOT allow for posting of a blank form w/out producing the following error.

Warning: Cannot modify header information - headers already sent

the reason i've been so fixated on this is that it expressly states in the book that there is a check to see if the form has data, and if not, the page is reloaded. halojoy, i should not have to rewrite the script-- this is not a function i'm laboring to implement into some application of my own-- it is merely an example written in a book, and i have been trying to figure out why it produces this error, when it specifically states the opposite-- that the page will be reloaded for the user to enter data if the form is blank.

so, i'm sorry to say that i really haven't learned anything from this. i have taken the advice that i've received in replies here, don't get me wrong-- i studied your workaround solutions, and i now know inside and out the logic on which this if statement is built

if ($_POST[op] != "send")

so, i guess i have learned something. it would have been nice if i could have learned why the author chose to use the

header("Location: sendmymail.php");

, but it's not really explained, just as the stripslashes usage is not explained.

and now, i've encountered another occurance of the

Warning: Cannot modify header information - headers already sent

from another example in the same book. it's because this is obviously the author's approach to this particular bit of script logic/ form control (that is, using the header("Location: reload bit). ugh! it's upsetting because there really is good content in this book! i have learned A LOT, but when it comes to the scripts, i feel like i'm walking on egg shells waiting for something to break, and yet it is so beyond my reach because i can't even figure out why the book's own scripts are erroneous, let alone, how to fix them!

sigh. i only hope that when / if i encounter this error on my own, the kind helpful people here at PHPBuilder.com will have mercy on me, and recall this ordeal!

grrr.