This page explains how to build programs containing both Fortran and C/C++ source code on OCTOPUS. Since runtime environments and standard libraries differ by language, you must specify the correct standard libraries when linking mixed-language programs.

Note that this guide uses the Intel oneAPI DPC++/C++ Compiler (icx/icpx) and Intel Fortran Compiler (ifx) included in the BaseCPU module.

Calling a C Function from a Fortran Main Program

Assume the main program is defined in "main.f90" and the function "hello" is defined in "hello.c" as follows.

main.f90

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program main   implicit none   interface     subroutine hello() bind(c)     end subroutine   end interface   call hello end program

hello.c

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#include <stdio.h>   void hello() {     printf("hello, world\n"); }

After compiling the source code with each language's compiler, link the objects with the Fortran compiler to generate an executable file.

ifx -c main.f90 # Compile Fortran source code
icx -c hello.c # Compile C source code
ifx -o hello main.o hello.o # Link objects

You can also link objects with the C compiler. In that case, use the -fortlib option to link the Fortran standard library.

icx -o hello -fortlib main.o hello.o # Link objects

Calling a C++ Function from a Fortran Main Program

Assume the main program is defined in "main.f90" and the function "hello" is defined in "hello.cpp" as follows.

main.f90

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program main   implicit none   interface     subroutine hello() bind(c)     end subroutine   end interface   call hello end program

hello.cpp

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#include <iostream>   extern "C" void hello() {     std::cout << "hello, world" << std::endl; }

After compiling the source code with each language's compiler, link the objects with the Fortran compiler to generate an executable file. At that time, link the C++ standard library using the -cxxlib option.

ifx -c main.f90 # Compile Fortran source code
icpx -c hello.cpp # Compile C++ source code
ifx -o hello -cxxlib main.o hello.o # Link objects

You can also link objects with the C++ compiler. In that case, use the -fortlib option to link the Fortran standard library.

icpx -o hello -fortlib main.o hello.o # Link objects

Calling a Fortran Subroutine from a C Main Function

Assume the main function is defined in "main.c" and the subroutine "hello" is defined in "hello.f90" as follows.

main.c

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extern void hello_();   int main() {     hello_();       return 0; }

hello.f90

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subroutine hello   implicit none     print *,'hello, world' end subroutine hello

After compiling the source code with each language's compiler, link the objects with the C compiler to generate an executable file. At that time, link the Fortran standard library using the -fortlib option.

icx -c main.c # Compile C source code
ifx -c hello.f90 # Compile Fortran source code
icx -o hello -fortlib main.o hello.o # Link objects

You can also link objects with the Fortran compiler. In that case, use the -nofor-main option to specify that the main program is not Fortran.

ifx -o hello -nofor-main main.o hello.o # Link objects