How to switch between URL variable names and values - php

Question

For example I have a URL like this one:
index.php?country=Canada
If it is just index.php that means that the default country is USA. People can switch between countries by checking or unchecking a checkbox.
But people can sort their results via GET variables:
State
Surname
Name
But if I use $_SERVER["REQUEST_URI"] then it will always just keep adding new values to my URL array (query string). It works if it is just index.php then I can make it like this:
State
Surname
Name
I know that after index.php it will always be a question mark ? first.
But what when visitors want to keep index.php?country=Canada and just switch between sort=state, sort=surname and sort=name. Then I need to know if a question mark is already in the URL, when to add & mark. I'm not sure how to solve this problem.

Answer 1

Change the way you echo your link:
PHP
<?php
$link = $_SERVER["PHP_SELF"];
if(isset($_GET['country']
$link.="&";
else
$link.="?";
?>
And echo link like this:
HTML
State
NOTE: I deleted the question mark before "sort".

Answer 2

You need logic to dynamically build a querystring, rather than statically adding ? and &.
Something like http_build_query would be the route I'd go, but the information you've provided is small compared with the possibilities you appear to want, so its hard to provide specific code.
Here is some more information about the http_build_query function in PHP. Its purpose is to build a querystring, here is an example of what you might do:
// capture the values into variables, however you want ($_GET is example)
$country = $_GET['country'];
$state = $_GET['state'];
$city = $_GET['city'];
$data = array();
// use logic to dynamically build the array, so long as the variables have values
!empty($country) ? array_push($data,'country'=>$country) : '';
!empty($state) ? array_push($data,'state'=>$state) : '';
!empty($city) ? array_push($data,'city'=>$city) : '';
// apply the array dynamically built
$querystring = http_build_query($data);
// concatenate to form the new URL
$url = 'http://www.example.com/?'.$querystring
If you declared country to be USA and city to be Seattle, but did not declare state, it would produce:
http://www.example.com/?country=USA&city=Seattle
Something along these lines should build the dynamic array you want with only the values you are looking for.

Answer 3

All of the variables in the query string are stored in the $_GET php superglobal array. In your example you can access the country with $_GET['country']. Do default to the USA you can use isset() to check if the variable exists.
$country = "USA";
if(isset($_GET['country'])) {
$country = $_GET['country'];
}

Answer 4

The solution here is to use either $_GET (already mentioned in another answer), or http://php.net/manual/en/function.parse-url.php, which makes the ordering of arguments completely irrelevant. Simply parse the url into an array of query arguments, and test for the ones you need. To turn it all back into a url, you would use http://php.net/manual/en/function.http-build-query.php