Update a paremeter in a url instead of adding a new one - php

Question

having a bit of trouble. Basically I have created some pagination. The problem is each time I click on a page number url it just adds the parameter to the url even if it already exists.
so for instance I land on the page. My url is now example.com/page?pagenum=1, I click the second page so my url is now example.com/page?pagenum=1&pagenum=2. Now it all works fine but as you can imagine is going to get a bit messy so would rather it update the parameter that's already in the URL. I'm currently using the following to get the current page URL:
<?php
function curPageURL() {
$pageURL = 'http';
if ($_SERVER["HTTPS"] == "on") {$pageURL .= "s";}
$pageURL .= "://";
if ($_SERVER["SERVER_PORT"] != "80") {
$pageURL .= $_SERVER["SERVER_NAME"].":".$_SERVER["SERVER_PORT"].$_SERVER["REQUEST_URI"];
} else {
$pageURL .= $_SERVER["SERVER_NAME"].$_SERVER["REQUEST_URI"];
}
return $pageURL;
}
?>
and then the Link is something like:
<a href='<?php echo curPageURL(); ?>&pagenum=<?php echo "1"; ?>'> 1 </a>
Update
I have other paremeters in the URL I need to keep, I only need to update 'pagenum'

Answer 1

The problem exists because REQUEST_URI contains both the path and query string, and you're appending a new query string to that every page turn. To extract the path, you could use this code, taken from this answer:
$path = strtok($_SERVER["REQUEST_URI"], '?');
You can then copy existing query string fields, but remove pagenum:
$fields = $_GET;
unset($fields['pagenum']); // remove any existing pagenum value
$path .= '?' . http_build_query($fields); // re-append the query string
You could then use more or less your existing link code:
<a href='<?php echo $path; ?>&pagenum=<?php echo "1"; ?>'> 1 </a>

Answer 2

You can use http_build_query like so:
$all_params = $_GET;
$all_params["page"] = "2";
$link = "page.php?" . http_build_query($all_params); // "page.php?page=2&foo=bar"