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How do i use eval function when the sentence has apostrophe (') in it?

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Hoon
Hoon on 27 Feb 2014
Commented: Steven Lord on 28 Oct 2019
I'm trying to use eval function with for loop
B1=sinc(x).*sinc(y);
B2=sinc(2x).*sinc(2y);
B3=sinc(3x).*sinc(3y);
B4=sinc(4x).*sinc(4y);
B5=sinc(5x).*sinc(5y);
for i=1:5
s=['imwrite(B' num2str(i) ','B_' num2str(i) '.bmp')']
eval(s);
end
But this sentence does not make sense since in some elements in "s" there are 3 apostrophe,
which is impossible for computer to compute.
Also, imwrite function got to have apostrophe for file name....
how do i make a breakthrough?

Accepted Answer

Jos (10584)
Jos (10584) on 27 Feb 2014
An apostrophe, or rather a single quote as it is called, in a string can be accomplished by doubling it, like in:
str = 'it''s me!'
More importantly, you do not want to use eval at all, by designing your variables a little bit more clever using, e.g., cell arrays or structs.
B(1).values = sinc(x).*sinc(y);
B(2).values = sinc(2x).*sinc(2y); % note that 2x is invalid syntax, but I do no know what you mean!
% B(3).values = . . . etcetera
for k = 1:numel(B)
filename = sprintf('B_%d.bmp',k)
imwrite(B(k).values, filename)
end
This away you avoid all the complications induced by eval ...

  2 Comments

Jacob Halbrooks
Jacob Halbrooks on 28 Feb 2014
+ 1 from me for Jos' answer. I agree that EVAL should be avoided when possible

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More Answers (3)

Jos (10584)
Jos (10584) on 28 Feb 2014
Edited: Jos (10584) on 28 Feb 2014
This is one of the reasons you should not use eval:
eval(char('fkur*)Ykvj"GXCN"{qw"pgxgt"mpqy"yjcv"jcrrgpu0"Kv"eqwnf"jcxg"hqtocvvgf"{qwt"jctfftkxg"000)+'-2)) ;

  2 Comments

Derrick Lim
Derrick Lim on 28 Oct 2019
Out of curiosity, what exactly does that command do? (Too scared to actually try it out)
Steven Lord
Steven Lord on 28 Oct 2019
Just run the part of that command starting with "char(" and ending with the closing parenthesis for the char function call. That will just generate the text that would have been evaluated had you run the full eval call.

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Jacob Halbrooks
Jacob Halbrooks on 27 Feb 2014
Edited: Jacob Halbrooks on 27 Feb 2014
If you need EVAL, I'd suggest using SPRINTF to form your expression. This lets you see the command you are writing more naturally and makes apostrophe management a little easier:
for i=1:5
s = sprintf('imwrite(%s, ''%s'')', ...
['B' num2str(i)], ['B_' num2str(i) '.bmp']);
eval(s);
end

Iain
Iain on 28 Feb 2014
Heres a third answer....
apostrophe = char(39);
then just use apostrophe
And a fourth answer:
If you actually want an apostrophe, and not a string start/termination character, you can use other apostrophes.
E.g, Alt+0145 = ‘ and Alt+0146 = ’

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