Programming and Data Types

Checking the Number of Function Arguments

The nargin and nargout functions let you determine how many input and output arguments a function is called with. You can then use conditional statements to perform different tasks depending on the number of arguments. For example,

function c = testarg1(a,b)
if (nargin == 1)
    c = a.^2;
elseif (nargin == 2)
    c = a + b;
end

Given a single input argument, this function squares the input value. Given two inputs, it adds them together.

Here's a more advanced example that finds the first token in a character string. A token is a set of characters delimited by whitespace or some other character. Given one input, the function assumes a default delimiter of whitespace; given two, it lets you specify another delimiter if desired. It also allows for two possible output argument lists.

function [token,remainder] = strtok(string,delimiters)
% Function requires at least one input argument
if nargin < 1
   error('Not enough input arguments.');
end
token = []; remainder = [];
len = length(string);
if len == 0
   return
end

% If one input, use white space delimiter
if (nargin == 1)
   delimiters = [9:13 32]; % White space characters
end
i = 1;

% Determine where non-delimiter characters begin
while (any(string(i) == delimiters))
   i = i + 1;
   if (i > len), return, end
end

% Find where token ends
start = i;
while (~any(string(i) == delimiters))
   i = i + 1;
   if (i > len), break, end
end
finish = i - 1;
token = string(start:finish);

% For two output arguments, count characters after
% first delimiter (remainder)
if (nargout == 2)
   remainder = string(finish + 1:end);
end

The strtok function is a MATLAB M-file in the strfun directory.

Note    The order in which output arguments appear in the function declaration line is important. The argument that the function returns in most cases appears first in the list. Additional, optional arguments are appended to the list.

How Functions Work

Passing Variable Numbers of Arguments