This example shows how to allow the users of your application to supply
options in files in addition to the command line.

The example consists of the following files:

options.cli
  Command line interface description in the CLI language.

options.hxx
options.ixx
options.cxx
  Command line interface implementation in C++. These files are generated 
  by the CLI compiler from options.cli using the following command line:

  cli --generate-file-scanner hello.cli

  We use the --generate-file-scanner CLI compiler option to include the 
  argv_file_scanner scanner implementation which provides support for 
  reading options from files in addition to the command line.

driver.cxx
  Driver for the example. It first creates the argv_file_scanner object 
  and indicates that the values for the --options-file option should be 
  recognized as files containing additional options. It then passes this
  scanner object to the option class which parses the command line. The
  driver then prints the option values.

test.ops
  Sample options file.

To run this example you can try the following command line:

$ ./driver --verbose 2 --val 1 --options-file test.ops --val 4

The output will be:

verbosity: 5
values: 1 2 3 4