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fortran-tcl86 – Tcl/Tk 8.6 for Fortran 2018

A work-in-progress Fortran 2018 ISO_C_BINDING interface library for interoperability with Tcl/Tk 8.6. This library allows you

  • to embed Tcl into Fortran,
  • to create Tcl extensions in Fortran (with Tcl Stubs),
  • to access (a subset of) the Tcl/Tk C API from Fortran,
  • to use Tcl as an evaluatable configuration file format, and
  • to add graphical user interfaces to Fortran programs.

There are some smaller differences to the original API:

  • Procedure names have been converted from camel case to snake case (for example, tcl_eval_ex() in Fortran instead of Tcl_EvalEx() in C).
  • Character strings passed to library procedures do not have to be null-terminated, as this step is done by Fortran wrappers.
  • Types are converted to their Fortran counter-parts (such as logical instead of c_int for boolean values).
  • Some procedure arguments have been made optional to avoid passing of c_null_ptr, c_null_funptr, and 0.
  • The interfaces called by the wrapper procedures contain a trailing underscore _ in their name (for example, wrapper tcl_eval() appends a null character to the second argument, then calls Fortran interface tcl_eval_()).
  • Functions and routines exposed to Tcl must have the bind(c) attribute.

See COVERAGE for a table of the bound procedures.

Fortran Libraries

Library Description
libftcl86.a Bindings to Tcl (libtcl86)
libftclstub86.a Bindings to Tcl Stubs for extensions in Fortran (libtclstub86)
libftk86.a Bindings to Tk (libtk86)

Build Instructions

Tcl 8.6 and Tk 8.6 with development headers have to be present. On FreeBSD, install the packages with:

# pkg install lang/tcl86 x11-toolkits/tk86

You will also need a Fortran 2018 and a C compiler. Then, execute the provided Makefile to build the static Fortran interface libraries libftcl86.a, libftclstub86.a, and libftk86.a:

$ make

By default, gcc and gfortran are used for compilation, but you can override the settings:

$ make CC=icc FC=ifort

Furthermore, it is possible to build a single static library libfortran-tcl86.a with fpm:

$ fpm build --profile=release --c-flag="`pkg-config --cflags tcl86`"

The include and library search paths in --c-flags have to point to the correct directories.

Linking Tcl & Tk

Linking depends on whether Fortran is called from Tcl or Tcl from Fortran. To build a Fortran program in example.f90 that invokes the Tcl interpreter, link against libftcl86.a -ltcl86:

$ gfortran -I/usr/local/include/tcl8.6/ -L/usr/local/lib/tcl8.6/ \
  -o example example.f90 libftcl86.a -ltcl86
$ ./example

The include and library search paths as well as the name of the Tcl 8.6 library itself may have to be changed depending on your operating system (-ltcl8.6 instead of -ltcl86 on Linux). Tcl/Tk can either be linked statically (libtcl86.a, libtk86.a) or dynamically (-ltcl86, -ltk86).

To create a shared library libexample.so with Tcl extensions written in Fortran, run:

$ gfortran -DUSE_TCL_STUBS -fPIC -shared -o libexample.so `pkg-config --cflags tcl86` \
  example.f90 libftcl86.a libftclstub86.a `pkg-config --libs tcl86`

To access the Tk toolkit from Fortran, link against libftk86.a libftcl86.a -ltk86 -ltcl86 (or, use pkg-config):

$ gfortran -DUSE_TK_STUBS `pkg-config --cflags tk86` \
  -o example example.f90 libftk86.a libftcl86.a `pkg-config --libs tk86`
$ ./example

Example

The following basic example just invokes the Tcl interpreter from Fortran to evaluate a character string:

! example.f90
program main
    use, intrinsic :: iso_c_binding, only: c_associated, c_ptr
    use :: tcl
    implicit none (type, external)

    integer     :: rc
    type(c_ptr) :: interp

    ! Create Tcl interpreter.
    interp = tcl_create_interp()
    if (.not. c_associated(interp)) stop 'Error: Tcl_CreateInterp() failed'

    ! Evaluate string as Tcl command.
    rc = tcl_eval_ex(interp, 'puts "Hello, from Tcl!"')
    if (rc /= TCL_OK) print '("Error: Tcl_EvalEx() failed")'

    ! Delete Tcl interpreter.
    call tcl_delete_interp(interp)
end program main

Compile and link the example with:

$ gfortran `pkg-config --cflags tcl86` -o example.f90 libftcl86.a `pkg-config --libs tcl86`
$ ./example
Hello, from Tcl!

Further Examples

The following example programs are provided:

  • config – Uses Tcl as a configuration file format (run config).
  • dict – Shows dictionary access (run dict).
  • eval – Evaluates a script in the Tcl interpreter (run eval).
  • fs – Tests Tcl file system API procedures (run fs).
  • library – Creates a Tcl extension hello inside a shared library (run script.tcl).
  • link – Demonstrates shared access to a variable between Tcl and Fortran (run link).
  • namespace – Creates a Tcl extension ::fortran::hello (with namespace) inside a shared library (run script.tcl).
  • re2c – Shows a Tk window to convert temperature values by calling an extension written in Fortran (run re2c).

To build the examples, run:

$ make examples

Change to the directory of an example before executing it.

Licence

ISC