How to know if an mcc-compiled MATLAB function is called in MATLAB or via standalone application?

I have a MATLAB function that has been compiled into a standalone application with mcc. When the user works with the function through the standalone application, output arguments are not used and instead I would like to ensure that the user gives an address to an output file as an input argument.

For instance, say my MATLAB function myFunc is defined like this:

function out_mat = myFunc(nElem, varargin)
save_file = false;
if nargin == 2
    save_file = true;
    add_to_file = varargin{1};
end
out_mat = rand(nElem);
if save_file
    % Write out_mat to address add_to_file....
end
end

When called in MATLAB, the user can define an output address (add_to_file) or not. It is up to the user and I do not care! But if the user is using the standalone executable, I want to make sure that the user actually defines add_to_file. So basically I want to add a condition like this to my code:

if call_in_matlab
    narginchk(1,2);
else
    narginchk(2,2);
end

How do I check if call_in_matlab is true or false? In other words, how can I tell in a function is called through its compiled standalone application or in MATLAB?

There are some functions in MATLAB to support Compiler-generated stand-alone programs. See the documentation. In particular, you want isdeployed.