How do I pass a 2D array in C++ to a Fortran subroutine?

Question

I am writing a small C++ program which passes a 2-D array (of complex numbers) to a Fortran subroutine and receives it back filled with values. I wrote a version which passe

Answer 1

The way to do this in this era is to use the ISO C Binding. Officially this is part of Fortran 2003, but is is widely supported by Fortran compilers, including gfortran. It even includes interoperability of complex types! See the list of types in the gfortran manual under the chapter "Intrinsic Modules", section "ISO_C_Binding". Plus there are several examples in the chapter "Mixed-Language Programming". On the C++ side, use extern C for the routine to be called in order to use C calling conventions without name-mangling. On the Fortran side, use the ISO C Binding. Then you will have compatibility at the language level rather than having to make assumptions about how the compilers work.