Dear all, I apologize in advance in case I did not do sufficient research, but I need feedback on a question regarding the ABI that does not seem handled by
https://gcc.gnu.org/onlinedocs/gfortran/Argument-passing-conventions.html How do we determine if an actual argument corresponding to a character, value, optional dummy argument is present or not? subroutine s (c) character, value, optional :: c end gets translated on x86_64-pc-linux-gnu to void s (character(kind=1)[1:1] c, integer(kind=8) _c) We could: - add a hidden logical argument for the present status as done for other types (this would clearly be an explicit ABI change) - use the passed character length: if it is > 0, then the argument is present, otherwise it is not. (This may require dealing with invalid code, where invocation of the subroutine with a character(len=0) actual argument is either diagnosed as done by the NAG compiler, or treated as undefined behavior.) Thanks, Harald
