Call a Function in Another Function, Prepare the Argument as a String

Hi there!

I have a function that takes input of the following form:

myFun({'.\file1.dat','.\file2.dat'},{'DataIdentifier'},'option','optionvalue')

I would like to create the input in another function and tried with creating this a character array:

function [  ] = myCall
%%Setup
myDir = './';
myIni = 'file';
myFiles = 1:10;
myLevel = '.dat';
myInterest = '{''var1''}';
myOptions = '''xvariable'',''y''';

%%Run
allFiles = '';
for i = myFiles
    allFiles = [allFiles  ''','''  myDir  myIni  '0'  char(string(i))  myLevel];
end
myString = ['{''' allFiles(4:end) '''}'];

myFun(myString,myInterest,myOptions)

end

Now, myFun returns

Error using fgets
Invalid file identifier. Use fopen to generate a valid file identifier.

Is there a general limitation in passing character arrays or strings as input to a function in MATLAB? Because, when I copy myString and paste it into myFun in the Command Window, it works.

Thank you very much in advance for your help on that matter! :)

[Stephen23]

http://web.archive.org/web/20210204134945/https://www.mathworks.com/matlabcentral/answers/736042-call-a-function-in-another-function-prepare-the-argument-as-a-string

[J.-B.]

Thank you very much for your indepth answer! It works like a charm!

Answer 1

[Stephen23]

"Is there a general limitation in passing character arrays or strings as input to a function in MATLAB?"

No, but the way you are calling that function is nothing like how you say it should be called.

How it should be called:

myFun({'.\file1.dat','.\file2.dat'},{'DataIdentifier'},'option','optionvalue')
%     ^^cell^array^of^char^vectors^,^^^^^^^ditto^^^^^^,^^^name-value^pairs^^^

How you are effectively calling it:

myFun('{''.\file1.dat'',''.\file2.dat''}','{''DataIdentifier''}','''option'',''optionvalue''')
%     ^^^^^one^character^vector^here^^^^^,^^^^second^char^vec^^^,^^^^third^char^vector^^

You are trying to turn all of the inputs into character vectors which look a bit like input arguments, but in fact you should just create those cell arrays exactly as they should be provided to the function (i.e. as cell arrays, do NOT turn them into character vectors which look a bit like cell arrays (that in turn look like they contain character vectors...)).

function [  ] = myCall
%%Setup
myDir = './';
myIni = 'file';
myLevel = '.dat';
myInterest = {'var1'}; % !!! actual cell array !!! 
myOptions = {'xvariable','y'}; % cell array -> used for comma-separated list.
%%Run
N = 10;
C = cell(1,N); % !!! preallocate actual cell array !!!
for k = 1:N % using SPRINTF and FULLFILE is much better than string concatenation:
    C{k} = fullfile(myDir,sprintf('%s%02d%s',myIni,k,myLevel));
end
myFun(C,myInterest,myOptions{:})
%     ^                          actual cell array of character vectors
%       ^^^^^^^^^^               actual cell array of character vectors
%                  ^^^^^^^^^^^^^ comma separated list:

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists