CALLING C ROUTINES FROM FORTRAN =============================== Machine C Routine name ------- ------------------ ALPHA/DUNIX lowercase letters_ (default) ALPHA/VMS anything CRAY UPPERCASE LETTERS HP lowercase letters (?) IBM/AIX lowercase letters (all IBM's ?) SGI/IRIX lowercase letters_ SUN lowercase letters_ TITAN UPPERCASE LETTERS VAX/VMS anything VAX/ULTRIX lowercase letters_ (default) Variable passing mechanisms --------------------------- Fortran usually passes its variables by reference (passes pointers). That means that you MUST give addresses in your calling C-program. Function results, may be passed by value, for example, the following code calls a FORTRAN function called "gamma": double x, y; .................. x = 2.0; y = gamma_(&x) Array storage order ------------------- Fortran uses a column wise storage of matrices while C stores them row wise. This means that when you want to pass a matrix from your C-program to the fortran routine you must transpose the matrix in your program before entering the routine. Of course, any output from such a routine must be transposed again. If you omit this step, then probably your program will run (because it has data to compute on) but it will generate wrong answers. Transposition is expensive, you may avoid it by adapting the source code, when the FORTRAN source says A(j+1,i+1) it could mean a[i][j] in C,. There are times when you don't want to modify already existing FORTRAN and C code, in such cases you may have to write a transposition wrapper. This can be advisable for reasons of clarity (i.e. keeping the documentation the code and the math in sync.) Array indexes ------------- Remember that array indexes in Fortran starts by default at 1 while in C they start at index 0; hence a passed array fortran_array[1:100] must be used in the C-routine/program as c_array[0:99]. Variable type matching ---------------------- Watch out especially with float's and double's. Make sure that the size of the variable in the calling program is identical to the size in the Fortran routine: float --- REAL (this is typical, but not always the case) double --- REAL*8
FORTRAN/C INTEROPERABILITY
FORTRAN/C INTEROPERABILITY | INTEROPERABILITY between FORTRAN & C | C , FORTRAN INTEROPERABILITY | Accessing FORTRAN classes in C
Subscribe to:
Post Comments (Atom)
No comments:
Post a Comment