Overriding TDRP parameters on the command line.

TDRP provides a mechanism to allow command line arguments to override parameter values set in the parameter file. This has the advantage of allowing the parameter-parsing logic to be applied to command line args rather than having to program separate logic to deal with the args.

The override mechanism uses a NULL-terminated array of strings, each of which is in the same format as an entry in the parameter file. The type tdrp_override_t is provided, along with a series of functions, to make it easy to create and use the override list.

Example

As an example, suppose the paramdef file contains the following:

  paramdef boolean {
    p_descr = "Option to print debugging messages";
  } debug;

The the paramfile could have the following entry:

  debug = FALSE;

Suppose a -debug appears on the command line. The following code fragment shows how you could set up and use the override:

  /* initialize before parsing the command line */

  tdrp_override_t override;
  TDRP_init_override(&override);

  /* in the arg parsing code */

  char tmp_str[BUFSIZ];
  int i;
  for (i =  1; i < argc; i++) {
    if (!strcmp(argv[i], "-debug")) {
      sprintf(tmp_str, "debug = TRUE;");
      TDRP_add_override(&override, tmp_str);
    }
  }

  /* loading the parameters */

  char *params_file_path;
  _tdrp_struct params;
  if (_tdrp_load_from_args(argc, argv, ¶ms,
			   override.list, ¶ms_file_path)) {
    fprintf(stderr, "ERROR - Problems with params file '%s'\n",
	    params_file_path);
    exit(-1);
  }

  /* free up the override list */

  TDRP_free_override(&override);

Each string in the override list is appended as a line to to the lines in the param file. The entry:

  debug = FALSE;

will still exist in the param file. However, this will be superceded by the line:

  debug = TRUE;

appended from the override list. Hence the debug value will be set to TRUE.

Program carefully and test fully

A word of caution here. As the programmer you need to make sure that your override code is generating strings which are valid as parameter entries. Test your code thoroughly, making sure you exercise every override option.