Would header () cause error if it's inside a function - php

Question

Assume I have a form on index.php and it points to test.php which process the data submitted.
index.php looks like the below:
<form action="test.php"></form>
It should cause an error if test.php looks like the below:
( As you can see, there is already an output Nice being sent before the header () )
echo 'Nice';
header ( "Location: https://example.com" );
But what if I put it inside a function and call the function?
echo 'Nice';
function process () {
header ( "Location: https://example.com" );
}
process ();
Would it works in this case since it's inside a function, and would it cause an error?

Answer 1

As stated here:
https://www.php.net/manual/en/function.header.php
Remember that header() must be called before any actual output is
sent, either by normal HTML tags, blank lines in a file, or from PHP.
It is a very common error to read code with include, or require,
functions, or another file access function, and have spaces or empty
lines that are output before header() is called. The same problem
exists when using a single PHP/HTML file.
So the problem would arise only because you called it after echoing text to the response while you had to do it before.
header ( "Location: https://example.com" );
echo 'Nice';
Calling it inside a function doesn't change that requirement, because the header is part of the response that you already sent echoing text.

Answer 2

Short answer:
header ( "Location: https://example.com" );
To:
echo "<script> window.location.href='https://example.com </script>" ;
The issue is that you are sending an output for the user to see "Nice!" before setting the redirect header. When you send Nice! The server is forced to send the packets with a Header already. You have to learn more about how HTTP protocol works.
The header is like the label on the envelop when you mail it via postal service. The content "Nice" is like the letter inside the envelope. You are trying to send a letter to your friend and then change the label address after it arrives.
Instead for that kind of functionality what you could do is use HTML or Javascript to make the redirect. (HTML way is an obsolete way) so I gave you the Javascript. However this is not good way of writing code but it works and I do it all the time.
Since you seem to like to output things after redirecting user you might want to buffer your output or simply give some time for the redirect to process:
<?php
echo 'Nice';
?> <!--NOTICE I CLOSED PHP TAG -->
setTimeout(function() {
window.location.href = ‘https://example.com/’;
},5000);
Please wait while we redirect you in 5 seconds or simply <a href="https://example.com">click here.<a>
<?php
echo "I like to write PHP code";
?>
It's so refreshing to see a year 2000 style of coding and redirects. :)
Cheers! Very Nice!!!

Answer 3

It might be useful to understand why there is an error if you call header() at the wrong time.
The response from your web server to a browser looks something like this, with a status, then "headers", then a "body":
HTTP/1.1 200 OK
Content-Type: text/html
Nice
When you call header(), you are asking the server to add a line next to the Content-Type, before the "body". (And adding a Location header in particular also changes the status code in the very first line from 200 to 301 to indicate a redirect.) Roughly like this:
HTTP/1.1 301 Redirected
Content-Type: text/html
Location: https://example.com
Nice
If the server has already sent the first version, because you told it to output "Nice", there's no way for it to "take it back" and send the second version. That's just as true in your second code as in your first: you're telling the server to output "Nice", and then telling it to go back and edit the headers, but it's too late.