How to eval an expression without an error?
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I would like to eval an expression, for example eval('x=a+b;'); But in case of non-existing a or b, I dont want to get an error, just do nothing.
回答（2 个）
Guillaume
2018-10-16
Not withstanding that using eval is a really bad idea, if you do really want to do it and not stop on error, wrap it in a try statement.
try
eval('x=a+b');
end
I'd recommend you catch the error, to check that it is indeed due to a missing variable and not some syntax error in your eval:
try
eval('x=a+b');
catch mexc
if ~strcmp(mexc.identifier, 'MATLAB:UndefinedFunction') %the exception you get for undefined function or variable
rethrow(mexc); %not the error we expected, really error as something else happened
end
end
Why not use the test for variables to exist
if exist('a') && exist('b')
x = a + b;
else
disp('did nothing')
end
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2023-12-5
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