I would like to encode some links for QR codes.
The shorter the link the better, because a shorter URL reduces the number of dots in the QR code, which makes it a lot easier to scan.
If I remove "http://www." from the start of my URLs (qoomerang.com/xxxx), the link works fine on my computer. But are standards these days such that I can safely remove them from the QR code aswell - i.e. will the text still be recognised as a website by all smartphones?
www is just a subdomain. Whether it's safe to drop this or not depends on the web server configuration. If the server is configured to serve a certain page on the www subdomain, it will need this.
(Refer to: https://superuser.com/questions/60006/what-is-the-purpose-of-the-www-subdomain for more details)
http:// refers to the protocol and should be retained as this is the only reliable way of identifying a web address and the method to fetch it. Some devices try to find URLs that do not contain http:// but you should not rely on this. Furthermore, the device would not know for certain whether it should use HTTP or HTTP over TLS (https://) to download the link.