GCompareFunc-compatible comparison for GDateTime's. Both GDateTime<-- -->'s must be non-NULL. Since 2.26
first GDateTime to compare
second GDateTime to compare
-1, 0 or 1 if dt1 is less than, equal to or greater than dt2.
See Implementation
GCompareFunc-compatible comparison for GDateTime's. Both GDateTime<-- -->'s must be non-NULL. Since 2.26