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How to use who within eval

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Qianyu
Qianyu on 9 Jan 2012
Edited: per isakson on 16 Feb 2017
Here is the code:
file_name = 'test';
eval(['file_length = length(who(''-file'',' file_name '));']);
But this doesn't work, because who requires a quoted string as a variable. Then I tried this,
eval(['file_length = length(who(''-file'', ''file_name'' ));']);
It didn't work, apparently. Now file_name showed up instead of the value I put in it. This sounds a very simple question, but I just don't know what to do. Help!

Accepted Answer

Andrew Newell
Andrew Newell on 9 Jan 2012
This is a working example:
clear
x = zeros(10,1); y = x;
save matlab.mat
file_name='matlab.mat';
eval('file_length = length(who(''-file'',file_name))')
file_length =
2
EDIT: Although I answered the question you asked, I agree with Sean and the Cyclist that it would be better not to use eval. See Loren's blog for some reasons.
  3 Comments
the cyclist
the cyclist on 10 Jan 2012
For example, even if you need the value of the looping variable in the file name, you can often use num2str() to convert the numeric to a string, and append it to the file name.

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More Answers (2)

Sean de Wolski
Sean de Wolski on 9 Jan 2012
Why use eval? Nothing in that statement looks like it couldn't be done without it.

the cyclist
the cyclist on 9 Jan 2012
Agree with Sean that you do not need eval() here. Try this:
file_name = 'test';
file_length = length(who('-file',file_name));

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