varargin
Variable-length input argument list
Syntax
Description
varargin
is an input variable in a
function definition statement that enables the function to accept any number of
input arguments. Specify varargin
by using lowercase
characters. After any explicitly declared inputs, include
varargin
as the last input argument.
When the function executes, varargin
is a
1-by-N cell array, where N is the number
of inputs that the function receives after the explicitly declared inputs. If the
function receives no inputs after the explicitly declared inputs, then
varargin
is an empty cell array.
Examples
Variable Number of Function Inputs
Define a function in a file named acceptVariableNumInputs.m
that accepts a variable number of inputs and displays the values of each input.
type acceptVariableNumInputs
function acceptVariableNumInputs(varargin) disp("Number of input arguments: " + nargin) celldisp(varargin) end
Call the function with several inputs.
acceptVariableNumInputs(ones(3),'some text',pi)
Number of input arguments: 3 varargin{1} = 1 1 1 1 1 1 1 1 1 varargin{2} = some text varargin{3} = 3.1416
varargin
and Declared Inputs
Define a function in a file named definedAndVariableNumInputs.m
that expects two inputs and accepts an additional number of inputs.
type definedAndVariableNumInputs
function definedAndVariableNumInputs(X,Y,varargin) disp("Total number of input arguments: " + nargin) formatSpec = "Size of varargin cell array: %dx%d"; str = compose(formatSpec,size(varargin)); disp(str) end
Call the function with several inputs.
definedAndVariableNumInputs(7,pi,rand(4),datetime('now'),'hello')
Total number of input arguments: 5 Size of varargin cell array: 1x3
Call the function with two inputs. varargin
is an empty cell array.
definedAndVariableNumInputs(13,42)
Total number of input arguments: 2 Size of varargin cell array: 0x0
Variable Number of Inputs and Outputs
Define a function in a file named variableNumInputAndOutput.m
that accepts a variable number of inputs and outputs.
type variableNumInputAndOutput
function varargout = variableNumInputAndOutput(varargin) disp(['Number of provided inputs: ' num2str(length(varargin))]) disp(['Number of requested outputs: ' num2str(nargout)]) for k = 1:nargout varargout{k} = k; end end
Call the function with two inputs and three outputs.
[d,g,p] = variableNumInputAndOutput(6,'Nexus')
Number of provided inputs: 2 Number of requested outputs: 3
d = 1
g = 2
p = 3
Call the function again with no inputs or outputs.
variableNumInputAndOutput
Number of provided inputs: 0 Number of requested outputs: 0
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.
Usage notes and limitations:
If you use
varargin
to define an argument to an entry-point (top-level) function, the code generator produces a C/C++ function with a fixed number of input arguments. The number of arguments that you specify when you generate code determines the fixed number of arguments.You cannot write to
varargin
. If you want to write to input arguments, first copy the input arguments into a local variable.The index into
varargin
must be a compile-time constant.
HDL Code Generation
Generate VHDL, Verilog and SystemVerilog code for FPGA and ASIC designs using HDL Coder™.
Usage notes and limitations:
You cannot write to
varargin
. If you want to write to input arguments, first copy the input arguments into a local variable.The index into
varargin
must be a compile-time constant.
Version History
Introduced before R2006aR2024b: Support for multi-indexing input arguments into cell arrays in HDL Coder
You can use the varargin
in a MATLAB Function
block that has the HDL block property Architecture set to
MATLAB Datapath
and multi-index input arguments into
cell arrays. For example, you can now generate HDL code for this code
snippet:
[x, y] = varargin{1:2};
R2023a: Improved performance when specifying zero or more inputs
Specifying a variable number of input arguments using varargin
shows improved performance. For example, in a file named
timingTest.m
in your current folder, create a function that
expects one input and accepts an additional number of inputs.
function timingTest(x,varargin) n = 1e6; tic for i = 1:n y = myFun(x,varargin{:}); end toc end function y = myFun(x,varargin) if nargin == 1 y = x; elseif nargin == 3 y = x + varargin{1} + varargin{2}; else y = NaN; end end
The amount of improvement depends on whether varargin
is
empty. The performance improvement is most significant when
varargin
is empty.
Empty
varargin
— Time this code by runningtimingTest(1)
. The code is about 22x faster than in the previous release. The approximate execution times are:R2022b: 0.404 s
R2023a: 0.018 s
Nonempty
varargin
— Time this code by runningtimingTest(1,2,3)
. The code is about 2x faster than in the previous release. The approximate execution times are:R2022b: 1.428 s
R2023a: 0.734 s
The code was timed on a Windows® 10, Intel® Xeon® CPU E5-1650 v4 @ 3.60 GHz test system.
R2022a: Generate HDL for MATLAB Function blocks with MATLAB Datapath architecture
You can generate HDL code for functions in MATLAB Function blocks with HDL block
property Architecture set to MATLAB
Datapath
. These functions can use input argument
varargin
. HDL function checkhdl
can
determine if cell arrays are accessed and initialized correctly using
varargin
.
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