Function Arguments :: Programming Tips (Programming)

Programming

Function Arguments

This section covers the following topics:

Getting the Input and Output Arguments

Use nargin and nargout to determine the number of input and output arguments in a particular function call. Use nargchk and nargoutchk to verify that your function is called with the required number of input and output arguments.

function [x, y] = myplot(a, b, c, d)
disp(nargchk(2, 4, nargin))           % Allow 2 to 4 inputs
disp(nargoutchk(0, 2, nargout))       % Allow 0 to 2 outputs

x = plot(a, b);
if nargin == 4
   y = myfun(c, d);
end

Variable Numbers of Arguments

You can call functions with fewer input and output arguments than you have specified in the function definition, but not more. If you want to call a function with a variable number of arguments, use the varargin and varargout function parameters in the function definition.

This function returns the size vector and, optionally, individual dimensions:

function [s, varargout] = mysize(x)
nout = max(nargout, 1) - 1;
s = size(x);
for k = 1:nout
   varargout(k) = {s(k)};
end

Try calling it with

```
[s, rows, cols] = mysize(rand(4, 5))
```

String or Numeric Arguments

If you are passing only string arguments into a function, you can use MATLAB command syntax. All arguments entered in command syntax are interpreted as strings.

```
strcmp string1 string1
ans =
     1
```

When passing numeric arguments, it is best to use function syntax unless you want the number passed as a string. The right-hand example below passes the number 75 as the string, '75'.

isnumeric(75)                   isnumeric 75
ans =                           ans =
    1                               0

For more information: See Passing Arguments in the MATLAB Programming documentation.

Passing Arguments in a Structure

Instead of requiring an additional argument for every value you want to pass in a function call, you can package them in a MATLAB structure and pass the structure. Make each input you want to pass a separate field in the structure argument, using descriptive names for the fields.

Structures allow you to change the number, contents, or order of the arguments without having to modify the function. They can also be useful when you have a number of functions that need similar information.

Passing Arguments in a Cell Array

You can also group arguments into cell arrays. The disadvantage over structures is that you don't have fieldnames to describe each variable. The advantage is that cell arrays are referenced by index, allowing you to loop through a cell array and access each argument passed in or out of the function.

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