Calling C from FORTRAN
The Unix portable Fortran-77 compiler ('f77') is written almost entirely in C.
The second pass of the compiler is the same one used by the C compiler, and
most 'f77' library routines are simply interfaces to corresponding C library
routines. However, since Fortran does not support data structures like those
used in C, you may not be able to take advantage of all the functionality that
the 'curses' library offers. Manipulating windows with 'curses' is especially
difficult. If you are interested in using routines involving data structures,
you should probably use C instead of Fortran.
To call C routines from a Fortran program, you will have to write some C code.
Fortran passes arguments by reference or address, so the C function has to be
prepared to accept the variable as an address. This means that you will have
to write functions in C that are called from Fortran that set up the arguments
properly before calling the library function. Schematically, this might be
something like this:
In the C source file:
foo_(bar) /* See below for information on the underscore! */
int *bar; /* Variables are passed by address. */
In the Fortran source file:
call foo(baz) /* Assuming that "baz" is an integer. */
The underscore is important because Fortran uses the character to keep
its symbols straight. If you are compiling on an RS6000 this is not
default behavior, but compiling with the -qextname option on the RS6000
will cause it to perform identical to the other platforms.
If you were calling the 'curses' routine 'move()', you might do
something like this:
The call to the C interface functions are made in the Fortran source file
(named 'test.f'):
call initscr()
call clear()
.
.
.
call move(x, y)
.
.
.
call refresh()
call endwin()
end
...where x and y are integers specifying the new coordinates.
The C source file (named 'curses.c') contains the interface routine to the
'curses' library function 'move()', along with the other C functions that
provide an interface to the some other 'curses' functions:
#include <curses.h>
initscr_()
{
initscr();
}
clear_()
{
clear();
}
move_(x, y)
int *x, *y; /* These are pointers */
{
move(*x, *y);
}
refresh_()
{
refresh();
}
endwin_()
{
endwin();
}
The routines are compiled by using these commands:
cc -c curses.c
f77 test.f curses.o -lcurses -ltermcap
If you are using macros defined in /usr/include/curses.h in your Fortran file,
be warned that they assume conventions of the C language. Be aware that this
may affect the results you obtain when using them in Fortran.
For more information, please see the section named "Inter-Procedure
Interface" on pp. 7-8 of the article "A Portable FORTRAN 77 Compiler".
The article is part of the Unix Programmer's Supplemental Documents,
Volume 1, which is in the Athena Reference Collection in Hayden or
Barker libraries (by the public Athena clusters there), or in the
Consultants' Office (1st floor N42).
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