nargin

Number of function input arguments

Syntax

nargin

nargin(fun)

Description

nargin returns the number of function input arguments given in the call to the currently executing function. Use this syntax in the body of a function only. When using an arguments validation block, the value returned by nargin within a function is the number of positional arguments provided when the function is called. For more information, see Use nargin Functions During Argument Validation.

nargin(fun) returns the number of input arguments that appear in the fun function definition. If the function includes varargin in its definition, then nargin returns the negative of the number of inputs. For example, if function myFun declares inputs a, b, and varargin, then nargin('myFun') returns -3.

If fun refers to a function that uses an arguments validation block, then the returned value is the number of declared positional arguments in the function definition as a non-negative value.

Examples

Inputs to Current Function

In a file named addme.m, create a function that accepts up to two inputs. Use nargin in the body of the function to determine the number of inputs.

type addme.m

function c = addme(a,b)
    switch nargin
        case 2
            c = a + b;
        case 1
            c = a + a;
        otherwise
            c = 0;
    end
end

At the command prompt, call the addme function with two inputs.

c = addme(13,42)

c = 
55

Call the function with one input.

c = addme(13)

c = 
26

Inputs Defined for a Function

Determine how many inputs a function accepts.

The function addme created in the previous example, has two inputs in its declaration statement (a and b). Define the name of the function as a character vector and use it as input for nargin.

fun = 'addme';
nargin(fun)

ans = 
2

Inputs to Function That Uses varargin

Determine how many inputs a function that uses varargin can accept.

In a file named mynewplot.m, create a function that accepts numeric inputs x and y and any number of additional plot inputs using varargin.

type mynewplot.m

function mynewplot(x,y,varargin)
    figure
    plot(x,y,varargin{:})
    title('My New Plot')
end

Query how many inputs newplot can accept.

fx = 'mynewplot';
nargin(fx)

ans = 
-3

The minus sign indicates that the third input is varargin. The mynewplot function can accept an indeterminate number of additional input arguments.

Input Arguments

fun — Function

function handle | character vector | string scalar

Function for which nargin returns the number of input arguments from its definition, specified as a function handle, a character vector, or a string scalar.

Example: @cos

Example: 'plot'

Data Types: char | function_handle

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• For the syntax nargin(fun), if fun is a function handle or a function name that C/C++ code generation does not support, then the generated code for nargin returns 0.

• C/C++ code generation does not support nargin(fun) for nested functions. If fun is a nested function, and no other function named fun exists as a local function or on the MATLAB^® path, code generation fails.

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

Version History

Introduced before R2006a