Php unkown error while trying to redirrect to another page using "header" function

Question

I have one "problem" with my code.I am building login page for school website and, when user clicks "logout" button it should reddirect them to page logout.php and i am using header("Location: login.php") but when someone clicks it this error appears

Warning: Cannot modify header information - headers already sent by (output started at D:\xampp\htdocs\testing\dodaci\menu.php:71) in D:\xampp\htdocs\testing\control_panel.php on line 28

But when i remove menu.php (It is navigation menu for my website, i included it in my website using PHP) Everything works fine.I don't know what is the problem.

** menu.php **

<div class="navigation">
           <ul id="menu">
    <li>
        <a href="index.php" style="margin-left:0px;">Naslovna </a>


    </li>
    <li>
        <a href="historijat.php">Historijat</a>
    </li>
    <li><font class="dropdown" >Zaposlenici<span class="icon icon-angle-down"></span></font>
        <ul class="sub-menu" style="width:170px;">
            <li>
                <a href="zaposlenici_profesori.php">Profesori</a>
            </li>
            <li>
                <a href="zaposlenici_pomocno_osoblje.php">Pomoćno osoblje</a>
            </li>



        </ul>

    </li>
    <li><font class="dropdown" >Sekcije<span class="icon icon-angle-down"></span></font>
        <ul class="sub-menu">
            <li>
                <a href="sekcije/informatika.php">Informatika</a>
            </li>
            <li>
                <a href="sekcije/matematika">Matematika</a>
            </li>

            <li>
                <a href="sekcije/biologija">Biologija</a>
            </li>

        </ul>

    </li>
    <li><font class="dropdown" >Upis u školu<span class="icon icon-angle-down"></span></font>
        <ul class="sub-menu" style="width:200px;">
            <li>
                <a href="Upis/gimnazija.php">Gimnazija</a>
            </li>
            <li>
                <a href="Upis/ekonomska.php">Ekonomska</a>
            </li>
            <li>
                <a href="Upis/sumarski_tehnicar.php">Šumarski tehničar</a>
            </li>
            <li>
                <a href="Upis/trgovacka.php">Trgovačka</a>
            </li>
            <li>
                <a href="Upis/tehnicka.php">Tehnička</a>
            </li>
        </ul>

    </li>

    <li> <a href="kontakt.php">Kontakt</a></li>
    <li><a href="#"><input style="width:145px;" type="text" name="t1" placeholder="Pretraga Učenika ..."/><input type="submit" name="submit" value="Traži" style="padding:0px 12px 0px 12px;"/></a>

    </li>


    </ul>


        </div>

Checkout the second paragraph http://php.net/manual/en/function.header.php. — Manolis Agkopian, Sep 17 '14 at 12:10
You cannot output any data to the screen before you send headers. Refer to the duplicates referenced above. — Edward, Sep 17 '14 at 12:10

score 0 · Answer 1 · answered Sep 17 '14 at 12:09

0

You can only post header() functions when no other data has been sent to the client.

When removing your menu.php file, I assume you do not send any information to the client before calling your header() function.

answered Sep 17 '14 at 12:09

Wampie Driessen

1,654
1
13
19

score 0 · Answer 2 · answered Sep 17 '14 at 12:10

In order for header() to work, it is required that no output is sent to the browser prior to calling the function. An output can be send even if no html is printed, but if you have a blank space outside of PHP tags, or if you use encoding with BOM.

If you MUST redirect, I suggest using the javascript alternative.

<script type="text/javascript">
<!--
window.location = "http://www.google.com/"
//-->
</script>

score 0 · Answer 3 · answered Sep 17 '14 at 12:10

0

As has been mentioned, any header call must be the first code to be reached on a page. Otherwise, you will have a problem.

You can try via JavaScript:

<script>window.location = 'http://www.mywebsite.com';</script>

answered Sep 17 '14 at 12:10

Ethan Turk

437
4
8

Php unkown error while trying to redirrect to another page using "header" function

3 Answers3