An SDL_GUID is a 128-bit identifier.
Defined in SDL_guid.h
typedef struct SDL_GUID {
16];
Uint8 data[ } SDL_GUID;
This is an acronym for "Globally Unique ID."
While a GUID can be used to assign a unique value to almost anything, in SDL these are largely used to identify input devices across runs of SDL programs on the same platform.If the device is detached and then re-attached to a different port, or if the base system is rebooted, the device should still report the same GUID.
GUIDs are as precise as possible but are not guaranteed to distinguish physically distinct but equivalent devices. For example, two game controllers from the same vendor with the same product ID and revision may have the same GUID.
GUIDs may be platform-dependent (i.e., the same device may report different GUIDs on different operating systems).