c++_calls_f90_test

c++_calls_f90_test, a C++ code 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 information on this web page is distributed under the MIT license.

Languages:

c++_calls_f90_test is available in a C version and a C++ version and a MATLAB version.

Related Data and Programs:

c_calls_f90_test, C programs which call a Fortran90 subroutine.

c++_calls_c_test, C++ codes which call a C function.

c++_calls_f77_test, C++ codes which call a Fortran77 subroutine.

f90_calls_c++_test, Fortran90 programs which call a C++ function.

KRONROD, a C++ code 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++ codes 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:

• c++_calls_f90_test.sh;

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, the source code.
• kronrod_test.sh, runs all the tests.
• kronrod_test.txt, the output file;

• kronrod.f90;