Check if a function handle is valid

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Ryan
Ryan 2014-7-1
评论： Steven Lord 2021-2-26
I use str2fun(...) to create a function handle from a user-inputted string. I want to be able to run a check to make sure the function created is valid and no typos were made. I could not find a way to do this. Any suggestions?
Thanks, Ryan
MATLAB R2014a
  1 个评论
Steven Lord
Steven Lord 2021-2-26
What is a "valid" function handle?
f = @quit; % NOTE: Don't execute f if you have data in your MATLAB session you need!
f is a "valid" function handle in that it won't error when called. But you may not want users to enter 'quit' as the user-inputted string and blindly evaluate that function handle -- the "Bobby Tables" scenario.
g = @() zeros(1:12); % MAY error or MAY succeed and take a LONG time doing so
This may successfully execute (though it may take a while) or may throw an error depending on your computer's memory availability and your MATLAB settings. Is it "valid"?

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采纳的回答

Kurt Schmutz
Kurt Schmutz 2014-9-18
Hi Ryan
To CHECK whether a function handle is valid or not (without trial-and-error) you can do the following:
f = str2func('nameofthefunction')
fh = functions(f)
if isempty(fh.file)
% invalid :(
else
% valid :)
end
Note: file "nameofthefunction.m" must be in the current folder
Cheers, Kurt
MATLAB R2013b
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显示 2更早的评论
Ryan
Ryan 2014-9-22
Thanks Kurt. This worked for me since the function being used will never be anonymous.
Ryan
David Sinex
David Sinex 2021-2-26
This fails if the function is a class member.

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更多回答（3 个）

Sean de Wolski
Sean de Wolski 2014-7-1
try
fun()
catch
disp 'didn''t work'
end
Try it and catch failures. Or provide a listbox with known functions to remove the human typing element.
Ryan
Ryan 2014-7-1
I thought about the try, catch method but I want to be more descriptive in the error returned. I do not know all the known functions as it is a user created function that they are using instead of a default one.
  1 个评论
Sean de Wolski
Sean de Wolski 2014-7-1
Well if you catch the MException, you could look at the message of it.
...
catch ME
ME.message
end

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Jos (10584)
Jos (10584) 2014-9-19
You might be interested in the function ISFUNCTION .

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