how to do a command line only if it is possible?

Question

Luigi Bruno 2016-8-9

1
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https://ww2.mathworks.cn/matlabcentral/answers/299017-how-to-do-a-command-line-only-if-it-is-possible

评论： John D'Errico 2016-8-9

Dear all, sorry for the "stupid" question. I am writing a code and sometimes happens that i want to recall a previous setting only if it exists, so i am using try as following

try setting=previous_setting; catch end

in this way if the previous setting exists it will used, if not nothing happens. Now i think that using try and catch is not so nice since it should be used for error tracing. Do you have any advice (i would not like to use if)? thank you all catch end

in this way if the previous setting exists it will used, if not nothing happens. Now i think that using try and catch is not so nice since it should be used for error tracing. Do you have any advice (i would not like to use if)? thank you all

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Answer 1

Thorsten 2016-8-9

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https://ww2.mathworks.cn/matlabcentral/answers/299017-how-to-do-a-command-line-only-if-it-is-possible#answer_231283

在 MATLAB Online 中打开

if exist('previous_setting')
end

If previous_setting is variable, use

exist('previous_setting', 1)

if it is an m-file, use

exist('previous_setting', h)

See

help exist

for further options.

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Luigi Bruno 2016-8-9

thank you for the answer. i would use the lowest number of strings in the code (this is why i dont want to use if). So if according to you there is no error to use try w/o catch i will proceed like that.

John D'Errico 2016-8-9

As I pointed out in the test though, exist is faster. If this is a question of milliseconds, it may not matter. Much time is spent by programmers looking for an optimal solution, when the cost is only a few milliseconds. Of course, if the code will be executed thousands or millions of times you should worry about the difference. But for something that will happen once, even one second of programmer time spent on the choice is a net waste of time.

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