C_CALLS_F90
C Main Program Calls FORTRAN90 Subroutines

C_CALLS_F90 is a directory of C programs which illustrates how a C main program can call a FORTRAN90 subroutine.

For this example, the KRONROD package is used. Note that the KRONROD library is available in C and in FORTRAN90, so this example is not created out of necessity (the C main program could have simply called the C version of KRONROD). Instead, it is intended as an example of how to do this when you have to (you don't have a C version of the routines you want to use.)

When calling a FORTRAN90 routine from a C function, there are some simple things that may be enough to guarantee success.

• a FORTRAN90 subroutine is like a C void function, and should be declared this way in the C code. The qualifier extern should also be used.
• a FORTRAN90 subroutine or function expects all its arguments to be passed by reference. This generally means simply that the C function must pass scalar variables by reference, not value.
• typically, when the FORTRAN90 compiler compiles the FORTRAN90 code, the names of functions and subroutines are stored with an appended underscore. In order for these names to be found by the C code, it is necessary that the C code declare and invoke the FORTRAN90 functions and subroutines with the underscore explicitly appended to the name.
• in many cases, a FORTRAN90 compiler is simply a "front end" to a corresponding C compiler, as in the case of the GNU compilers gfortran and gcc, or the Intel compilers ifort and icc. This means that, as long as the corresponding compilers are used to compile the FORTRAN90 and C codes, it is probably possible to use either compiler to link and load the object codes; however, the load command may need to specify explicitly certain libraries associated with one of the languages. For instance, if loading using the gcc command, it is necessary to include "-l gfortran" so that the FORTRAN90 I/O libraries, among others, are included in the build.

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Languages:

C_CALLS_F90 is available in a C version and a C++ version and a MATLAB version.

Related Data and Programs:

C_CALLS_F77, is a directory of C programs which illustrates how a C program can call a FORTRAN77 subroutine.

C++_CALLS_F77, C++ programs which illustrate how a C++ main program can call a FORTRAN77 subroutine.

C++_CALLS_F90, C++ programs which illustrate how a C++ main program can call a FORTRAN90 subroutine.

F77_CALLS_C, FORTRAN77 programs which illustrates how a FORTRAN77 program can call a C function.

F77_CALLS_C++, FORTRAN77 programs which illustrates how a FORTRAN77 program can call a C++ function.

F90_CALLS_C, FORTRAN90 programs which illustrates how a FORTRAN90 program can call a C function.

F90_CALLS_C++, FORTRAN90 programs which illustrates how a FORTRAN90 program can call a C++ function.

KRONROD, a C library which can compute a Gauss and Gauss-Kronrod pair of quadrature rules of arbitrary order, by Robert Piessens, Maria Branders.

KRONROD, a FORTRAN90 library which can compute a Gauss and Gauss-Kronrod pair of quadrature rules of arbitrary order, by Robert Piessens, Maria Branders.

MATLAB_CALLS_C, MATLAB programs which call a C function, using MATLAB's MEX facility.

MIXED, C programs which call a function written in another programming language.

Reference:

• Calling FORTRAN Subroutines from Fortran, C and C++,
  Fritz Keinert,
  Mathematics Department,
  Iowa State University.

Source Code:

KRONROD is the FORTRAN90 source code for the KRONROD library. It should be essentially unchanged from the standard version.

• kronrod.f90;

KRONROD_test is the C source code for the main program. Some changes have been made from the standard version in order to adjust for the fact that we are calling a FORTRAN90 subroutine.

• kronrod_test.c;

Examples and Tests:

• kronrod_test.txt, the output file;

You can go up one level to the C source codes.