I am developing a cross platform game for which I needs to generate unique identifier (User ID) for each user. I known some platform (Android or iOS) specific approaches to get device related identifiers but I am looking for a solution independent of the device identifiers.
User ID Requirements:
1. Independent of the device's platform
2. Offline implementation (no communication with any servers)
3. Without sign-up process
I have implemented one approach to create User IDs where I store the system time when the game was launched for the first time on the device.
I have following questions:
1. Are there any other approaches to generate User IDs (which will meet the above requirements)?
2. What are the common approaches to create unique identifiers with taking any information from the user?
3. Are there any third party plug-ins to implement User IDs?
I would appreciate any suggestions and thoughts on this topic.
EDIT:
There are lot of responses to use UUID/GUID. Generally, this approach looks fine but I am looking for a solution which can generate same User ID even if the user reinstall the game.