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 g++, or the Intel compilers ifort and icpp. 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_F90, C programs which call a FORTRAN90 subroutine.

C++_CALLS_C, C++ programs which call a C function.

C++_CALLS_F77, C++ programs which call a FORTRAN77 subroutine.

F90_CALLS_C++, FORTRAN90 programs which 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.

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 FORTRAN77 subroutine.

• kronrod_test.cpp;

Examples and Tests:

• kronrod_test.txt, the output file;

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