http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49630
--- Comment #2 from Hans-Werner Boschmann <boschmann at tp1 dot physik.uni-siegen.de> 2011-07-04 19:29:50 UTC --- "C417: A function name shall not be declared with an asterisk type-param-value unless it is of type CHAR- ACTER and is the name of the result of an external function or the name of a dummy function." So it is allowed to put an assumed character length into an interface, but not in the way as I did in the code above. My example is invalid. But how would I declare an abstract interface of a function with variable length? I am allowed to use any scalar integer expression as length parameter of a character function, but I cannot leave it empty in the interface. That's why I use character(:),allocatable::res with the NAG fortran compiler. As far a I know, this is the only valid way and that's why I am looking forward for gfortran to implement it.