Runtime Error

What This Error Means

This error occurs when PHP tries to send HTTP headers after the output has already started. In PHP, headers must be sent before any content is output.

Why It Happens

This error typically happens when PHP code attempts to output something before the headers have been sent. This could be due to echo statements, print statements, or even whitespace before the PHP opening tag. It can also occur when using functions that output data, like the var_dump() function.

How to Fix It

1. 1To fix this error, you need to move any output-related code before sending the headers. This can be achieved by using the ob_start() function to turn on output buffering, or by moving echo statements and other output functions to the top of the script. Additionally, ensure that there are no whitespace characters before the PHP opening tag.

Example Code Solution

function sendHeaders() {
    echo 'Content-Type: text/html';
}
sendHeaders();
echo 'Hello World!';

function sendHeaders() {
    header('Content-Type: text/html');
}
sendHeaders();