You can freely mix FTN95 and FTN77 compiled code and either or both can do the
However, in general the I/O systems in Fortran and C/C++ are different and
should not be mixed. For example, it is not usually possible to open a file in
FTN95, and then pass the handle to be used in C/C++. The only exception to this
rule is that if you use DBOS library calls to manipulate files, then the
handles are common across the language boundary.