What is the neatest way of passing flags to a Matlab function?

Question

I'm designing a function that takes as argument one structure and any number of flags. The function will contain a couple of ifs checking whether a specific flag is set.

What is the neatest way to achieve this? I was thinking about passing the flags as separate string arguments. Is there a neater solution?

Oli · Accepted Answer · 2011-12-21T22:54:53.833

3

I would do it like using varargin and ismember:

function foo(arg1,arg2,varargin)

  flag1=ismember('flag1',varargin);
  flag2=ismember('flag2',varargin);
  flag3=ismember('flag3',varargin);

And you can call the function like that:

foo(a1,a2,'flag3','flag1')

This will activate flag1 and flag3.

edited Dec 21 '11 at 22:54

answered Dec 21 '11 at 22:36

Oli

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Andrey Rubshtein · Answer 2 · 2011-12-21T22:37:38.230

2

Probably you can pass varargin - The even will be names of the flags and the odd their values (except the first)

function Foo(st, varargin)

end

Then pass values like this:

Foo(st, 'Flag1', true, 'Flag2', false)
Foo(st, 'Flag3', true, 'MyFlag2', false,'MySpecialFlag',false)
Foo(st)

To access the variable arguments use

varargin{2}, varargin{3},

etc..

To check whether a specific flag was passed, do

flagNames = varargin{2:end};
ismember('MyFlag',flagNames )

edited Dec 21 '11 at 22:37

answered Dec 21 '11 at 22:14

Andrey Rubshtein

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Is there a simple way of checking whether a specific flag was passed or not? – Tim Dec 21 '11 at 22:35

score 2 · Answer 3 · answered Dec 21 '11 at 22:27

Pass in a struct of flags:

options = struct(...
    'Flag1', true, ...
    'Flag2', true, ...
    'MySpecifFlag', false ...
);

Foo(st, options);

To get a list of all the flags that were explicitly set by the user, use fieldnames:

passedOptions = fieldnames(options);

This returns a cell array whose elements are strings - these strings are the flags set by the user; the ith element of the array is the ith flag set by the user.

Access the value of each flag that was set:

options.(passedOptions{i}) %# gets the value of the flag corresponding to passedOptions{i}

score 1 · Answer 4 · answered Dec 21 '11 at 22:38

You can pass the flags as a string with 0s and 1s. The order can be fixed or you can also pass a cell array of flag names.

flagstr = '101'; %# string passed as argument
flaglog = flagstr=='1'; %# logical vector, can be accessed as flaglog(i)
fname = {'flag1','flag2','flag3'}; %# flag names, can be passed as argument or defined in the function
fvalue = num2cell(flaglog); %# create cell array
flags = cell2struct(fvalue, fname, 2); %# create a structure, so you can access a flag with flags.flag1

You need to take care to match the length of fvalue and fnames. if they are different you can either generate an error or somehow correct it (remove the extra flags or fill the absent by default value).

score 0 · Answer 5 · answered Dec 21 '11 at 23:19

0

varargin is the way to go for parsing a variable number of arbitrary input arguments. If you want somemore control over the calling syntax of the function (i.e. optional/required arguments) then I suggest looking into Matlab's input parser.

answered Dec 21 '11 at 23:19

Chris

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What is the neatest way of passing flags to a Matlab function?

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