How to execute only one of multiple redundant matlab functions?

Question

Stefan 2015-1-8

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https://ww2.mathworks.cn/matlabcentral/answers/169306-how-to-execute-only-one-of-multiple-redundant-matlab-functions

回答： Guillaume 2015-1-8

采纳的回答： Guillaume

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Dear reader,

Given a succession of multiple redundant commands, for example

    cprintf('blue', '!! This is a message !!');   
    disp('!! This is a message !!');

I would like to be able to execute the first one of them and disregard the rest. However, assuming the file cprintf.m is not available on the system, matlab will issue an error and this is precisely what I want to avoid. So, alternatively, I would like to execute the second line which represents the fallback solution, avoiding the error.

Given this scenario, here is my question: how can I achieve this?

I assume I need to write a function, let's call it alternatives.m which should take as arguments both previous functions:

     alternatives('cprintf('blue', '!! This is a message !!')','disp('!! This is a message !!')')

but I wouldn't know how to write the code.

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Answer 1

Guillaume 2015-1-8

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Probably the easiest way is to use try ... catch statements. The alternative would be to use exists and co.

function alternatives(varargin)
    for statement = varargin
       try
          eval(statement{1});
          return;
       catch 
       end
   end
   error('none of the statement succeeded');
end

But, rather than using statement strings for which you don't get syntax correction, I would use function handles, like this:

alternatives(@() cprintf('blue', '!! This is a message !!'), @() disp('!! This is a message !!'));

The code for the function is then:

function alternatives(varargin)
    for statement = varargin
       try
          statement{1}();
          return;
       catch 
       end
   end
   error('none of the statement succeeded');
end

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Answer 2

Adam 2015-1-8

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try
    cprintf('blue', '!! This is a message !!');   
catch err
    disp('!! This is a message !!');
end

should work, though you can extend it if you want to only catch certain errors such as cprintf not existing, etc.

That is why I put the 'err' variable there, from which you can get the error id and respond only to certain errors and rethrow in the case of others etc.

If you just want to catch all errors and always do the alternative code though you can just remove the unused 'err' variable