(octave.info)Variable-length Argument Lists

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11.4 Variable-length Argument Lists
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Sometimes the number of input arguments is not known when the function
is defined.  As an example think of a function that returns the smallest
of all its input arguments.  For example:

     a = smallest (1, 2, 3);
     b = smallest (1, 2, 3, 4);

In this example both ‘a’ and ‘b’ would be 1.  One way to write the
‘smallest’ function is

     function val = smallest (arg1, arg2, arg3, arg4, arg5)
       BODY
     endfunction

and then use the value of ‘nargin’ to determine which of the input
arguments should be considered.  The problem with this approach is that
it can only handle a limited number of input arguments.

   If the special parameter name ‘varargin’ appears at the end of a
function parameter list it indicates that the function takes a variable
number of input arguments.  Using ‘varargin’ the function looks like
this

     function val = smallest (varargin)
       BODY
     endfunction

In the function body the input arguments can be accessed through the
variable ‘varargin’.  This variable is a cell array containing all the
input arguments.  Note: Cell Arrays, for details on working with cell
arrays.  The ‘smallest’ function can now be defined like this

     function val = smallest (varargin)
       val = min ([varargin{:}]);
     endfunction

This implementation handles any number of input arguments, but it’s also
a very simple solution to the problem.

   A slightly more complex example of ‘varargin’ is a function
‘print_arguments’ that prints all input arguments.  Such a function can
be defined like this

     function print_arguments (varargin)
       for i = 1:length (varargin)
         printf ("Input argument %d: ", i);
         disp (varargin{i});
       endfor
     endfunction

This function produces output like this

     print_arguments (1, "two", 3);
          ⊣ Input argument 1:  1
          ⊣ Input argument 2: two
          ⊣ Input argument 3:  3

 -- : [REG, PROP] = parseparams (PARAMS)
 -- : [REG, VAR1, ...] = parseparams (PARAMS, NAME1, DEFAULT1, ...)
     Return in REG the cell elements of PARAM up to the first string
     element and in PROP all remaining elements beginning with the first
     string element.

     For example:

          [reg, prop] = parseparams ({1, 2, "linewidth", 10})
          reg =
          {
            [1,1] = 1
            [1,2] = 2
          }
          prop =
          {
            [1,1] = linewidth
            [1,2] = 10
          }

     The parseparams function may be used to separate regular numeric
     arguments from additional arguments given as property/value pairs
     of the VARARGIN cell array.

     In the second form of the call, available options are specified
     directly with their default values given as name-value pairs.  If
     PARAMS do not form name-value pairs, or if an option occurs that
     does not match any of the available options, an error occurs.

     When called from an m-file function, the error is prefixed with the
     name of the caller function.

     The matching of options is case-insensitive.

     See also: Note: varargin, *note inputParser:
     XREFinputParser.