XL Fortran Enterprise Edition for AIX : User's Guide - IBM

Notes:
1. In interlanguage communication, it is often necessary to use the %VAL and
%REF built-in functions that are defined in “Passing Arguments By Reference
or By Value” on page 353.
2. C programs automatically convert float values to double and short integer
values to integer when calling an unprototyped C function. Because XL Fortran
does not perform a conversion on REAL(4) quantities passed by value, you
should not pass REAL(4) and INTEGER(2) values as arguments to C functions
that you have not declared with function prototypes.
3. The Fortran-derived type, the Pascal RECORD, and the C structure must match
in the number, data type, and length of subobjects to be compatible data types.
Related Information: One or more sample programs under the directory
/usr/lpp/xlf/samples illustrate how to call from Fortran to C.
To use the Fortran 2003 Draft Standard interoperability
features provided by XL Fortran, see the Language
Interoperability Features section in the XL Fortran Enterprise
Edition for AIX Language Reference.
Passing Global Variables between Languages
To access a C data structure from within a Fortran program or to access a common
block from within a C program, follow these steps:
1. Create a named common block that provides a one-to-one mapping of the C
structure members. If you have an unnamed common block, change it to a
named one. Name the common block with the name of the C structure.
2. Declare the C structure as a global variable by putting its declaration outside
any function or inside a function with the extern qualifier.
3. Compile the C source file with -qalign=packed.
program cstruct struct mystuff {
real(8) a,d double a;
integer b,c
int b,c;
. double d;
. };
common /mystuff/ a,b,c,d
. main() {
.
end }
If you do not have a specific need for a named common block, you can create a
sequence-derived type with the same one-to-one mapping as a C structure and
pass it as an argument to a C function. You must compile the C source file with
-qalign=packed.
Common blocks that are declared THREADLOCAL are thread-specific data areas
that are dynamically allocated by compiler-generated code. A static block is still
reserved for a THREADLOCAL common block, but the compiler and the
compiler’s run-time environment use it for control information. If you need to
share THREADLOCAL common blocks between Fortran and C procedures, your
C source must be aware of the implementation of the THREADLOCAL common
block. For more information, see THREADLOCAL common blocks, the Directives
section in the XL Fortran Enterprise Edition for AIX Language Reference, and
Appendix A, “Sample Fortran Programs,” on page 405.
350 XL Fortran Enterprise Edition for AIX : User’s Guide