How to include php files containing "session_start()", "echo", etc., in another php file without the "headers already sent" error?

Question

I have already investigated here in Stack about such error, but I have not found a way to solve my specific problem.

I have a file saved as PHP that works as an "index", basically full of HTML. About halfway through the structure of the file, in body, I want to insert a visit counter into the site and an online user display. I made a PHP file for each of these two things and included (with "include") within this "index". However, the following error occurred:

"Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at C:\wamp64\www\administrador\indexadmin.php:192) in C:\wamp64\www\administrador\usuariosonline.php on line 3
Call Stack
#   Time    Memory  Function    Location
1   0.0007  244648  {main}( )   ...\indexadmin.php:0
2   0.0050  265496  include( 'C:\wamp64\www\administrador\usuariosonline.php' ) ...\indexadmin.php:206
3   0.0050  265544  session_start ( )   ...\usuariosonline.php:3"

How to solve?

Here are the codes:

"index.php" is this (no body):

<div class="col col-3">
<div class="visitassite">

    <h4>Visitas ao Site</h4>        

    <p>

    <?php include "totalvisitas.php"; ?>

    </p>
</div>
</div>


<div class="col col-3">
<div class="usuariosonline">

    <h4>Usuários Online</h4>        

    <p>

    <?php include "usuariosonline.php"; ?>

    </p>
</div>
</div>

The two php files that are being included are these:

Filing cabinet total visits.php:

<?php
try {
    $pdo = new PDO('mysql:host=localhost;dbname=contador', 'root', '');
}catch (PDOException $e){
    echo $e->getMessage();
}
$selecionar = $pdo->prepare("SELECT * FROM visitas");
$selecionar->execute();
$resultados = $selecionar->fetchAll(PDO::FETCH_ASSOC);
foreach($resultados as $results):
    echo "Total de visitas ao site: ".$results['visitas'];
    $contar = $results['visitas'] + 1;
    $update = $pdo->prepare("UPDATE visitas SET visitas=:visitas");
    $update->bindValue(':visitas', $contar);
    $update->execute();
endforeach;
?>

The other is this one (usuariosonline.php):

<?php
session_start();
$session_path = session_save_path();
$visitors=0;
$handle = opendir($session_path);
while (($file = readdir ($handle)) != FALSE)
{
    if ($file!="."&&$file!="..")
    {
        if (preg_match("/^sess/",$file))
        $visitors++;
    }
}
echo "Há $visitors visitantes online.";
?>

Answer 1

To resolve session related error another approach can be used. Basically you create a new file, for example php session. and place the following content:

//chama o session_start apenas se não tiver sido chamado anteriormente
function iniciar_sessao(){
    if(!(session_status() === PHP_SESSION_ACTIVE)){
        session_start();
    }
}

With this you can remove all calls to session_start in the other files, and move to incluit at the top of each file (in the first line)

require_once 'sessao.php';
iniciar_sessao();

It won’t be a problem if you call it more than once, because the function iniciar_sessao() already makes the appropriate treatment.

Answer 2

Man, I’d change the way I do it.

1. would bring the includes to the top of the file
2. inside includes, in place of echo would throw the results for variables
3. finally where the includes were, would echo the variables created by the includes.