The aot_out_module provides some convenience functions to output data into nested Lua tables. It purely relies on Fortran formatted IO, and therefore could also be used without the Lua library. Despite its high independence from the rest of the library it can be considered as a counter part to the reading functions. That is Aotus allows you to use Lua as a closed system, where you store values from one Fortran application in a script and read it back in another Fortran application using Lua. This yields a great flexibility and allows you to design easily extendable and portable file exchanges.

Writing a Lua Script

The output mechanism relies on a file-handle described by the aot_out_type. It is initialized with:

call aot_out_open(put_conf, filename, outUnit, indentation)


  • put_conf: is the handle to the opened output file
  • optional filename: name of the file to write to
  • optional outUnit: Pre-Connected file unit to write to
  • optional indentation: Number of spaces to use for indentation (defaults to 4).

You either have to state the filename or the outUnit, if both are given, the filename will be used and outUnit ignored. When you specify a filename to open, the according file will be replaced, if it exists and opened for writing.

After putting all values into the script, the output has to be finished with

call aot_out_close(put_conf)

This will close the given handle and, if the file was opened it is closed as well.

The concept of writing into the Lua script is very similar to the reading. Values are written by calling aot_out_val, which is a generic interface for the various intrinsic types in Fortran, except complex numbers. The interface for scalar values looks like this:

call aot_out_val(put_conf, val, vname, advance_previous)


  • put_conf: is the handle to the output file
  • val: value to write
  • optional vname: A name to assign to this value.
  • optional advance_previous: Flag if the value should be put on a new line.

Arrays will be put into tables internally, and the interface looks slightly different:

call aot_out_val(put_conf, val, vname, advance_previous, max_per_line)

Where all parameters have the same meaning as in the scalar interface, and the additional optional parameter max_per_line indicates how many entries of the array should be put on a common line. If none is provided some default depending on the data type will be used. The opening bracket of the table will always be on the same line as the first entry, and the closing bracket on the same line as the last entry.

Writing to Tables

To put values into arbitrarily nested tables, there are opening and closing calls for the tables, all values in between these two calls will be put into this table. Again this handling of tables is similar to the interface used in the input routines. Opening a table is done with:

call aot_out_open_table(put_conf, tname, advance_previous)


  • put_conf: is the handle to the script to write into
  • optional tname: Optionally a name might be assigned to the table
  • optional advance_previous: A flag to indicate if this table should be started on a new line (default = .true.)

To close the table again the following call has to be used:

call aot_out_close_table(put_conf, advance_previous)


  • put_conf: is the handle to the script to write into
  • optional advance_previous: A flag to indicate the closing bracket should be put on a new line (default = .true.)


Here is a short example how this could be used in Fortran:

program aot_out_test
  use aot_out_module

  implicit none

  type(aot_out_type) :: dummyOut

  call aot_out_open(put_conf = dummyOut, filename = 'dummy.lua')

  call aot_out_open_table(dummyOut, 'screen')
  ! Screen table
  call aot_out_val(dummyOut, 123, 'width')
  call aot_out_val(dummyOut, 456, 'height')

  call aot_out_val(dummyOut, [100.0, 0.0], vname='origin')
  ! End of screen table
  call aot_out_close_table(dummyOut)

  call aot_out_val(dummyOut, [0, 1, 2, 3], vname='testarray')

  call aot_out_close(dummyOut)
end program aot_out_test

And here is the resulting Lua script:

screen = {
    width = 123,
    height = 456,
    origin = { 100.00000000, 0.00000000 } 
testarray = { 0, 1, 2, 3 }