Refresh page and change 1 $_GET variable

Question

I've been wondering this for a while since I started PHP. Some sites use filtering options. Sometimes some of those filters are completely random. For example someone might be viewing: products.php?c=1&p=1&s=100 In that example, let's assume c is the category, p is the page and s is the start price.

If the viewing user were to change the start price or flip to the next page using a hyperlink, how would one change only a single $_GET[] variable while leaving the others untouched. I do have a small script in PHP to obtain the current URI however, I just can't figure out how I'd change only that variable while keeping the others untouched and refresh the page? I've looked at substr(), strpos(), and ereg_replace() and I just can't figure it out!

I am really sorry if this is a dumb question, I feel like I've missed something really easy that can fix this but I'm genuinely stuck guys.

Thanks so much in advance! Mike.

Answer 1

It depends on whether or not you're in a form or a URL.

If you're in a form it's easy because the user changes the input field they want changed and the others stay there:

<form>
    <input type="p" value="1" />
    <input type="c" value="1" />
    <input type="s" value="100" />
    <input type="submit" />
</form>

The problem with the URL based method is you would have to set the url for each one like this:

<a href="?p=1&c=1&s=1">$1 Starting Price</a>
<a href="?p=1&c=1&s=10">$10 Starting Price</a>
<a href="?p=1&c=1&s=100">$100 Starting Price</a>

You'd have to do this to make it dynamic:

<a href="?p=<?php echo urlencode($_GET['p']) ?>&c=<?php echo urlencode($_GET['c']) ?>&s=1">$1 Starting Price</a>

That's a lot of typing for all of your links. You could make a PHP function to handle changing the one value like this:

function genUrl($newKey, $newVal) {
    $url = '?';
    foreach ($_GET as $key => $val) {
        if ($url != '?') {
            $url .= '&';
        }

        $url .= urlencode($key) . '=' ($key == $newKey ? $newVal : urlencode($val));
    }

    return $url;
}

And your html would look like this:

<a href="<?php echo genUrl('s', 1) ?>">$1 Starting Price</a>
<a href="<?php echo genUrl('s', 10) ?>">$1 Starting Price</a>
<a href="<?php echo genUrl('s', 100) ?>">$1 Starting Price</a>

Answer 2

You just need to have your hyperlinks location set up to the variable you like to change. Say if it is currently products.php?c=1&p=1&s=100 and you wanna go to products.php?c=2&p=1&s=100 then you need to have your anchor tag like so

<?php

$_GET['c'] = $_GET['c']++;

?>

<a href='<?php echo "products.php?c={$_GET['c']}&p=1&s=100" ?>'>link<a/>

It is identical with other variables.