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

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?

[Jos (10584)]

http://www.mathworks.nl/help/matlab/matlab_prog/string-evaluation.html

[Stephen Cobeldick]

Ugh. Do NOT use eval for such trivial code.

See Jos's answer below for the best way to do this (best in the sense faster, neater, less buggy, more efficient, easier to debug, more secure).

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

Answer 1

[Jos (10584)]

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 ...

[Hoon]

God, both answers are great! How can i choose both?

[Jacob Halbrooks]

+ 1 from me for Jos' answer. I agree that EVAL should be avoided when possible

Answer 2

[Jos (10584)]

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)) ;

Also see: http://www.mathworks.nl/help/matlab/matlab_prog/string-evaluation.html

[Derrick Lim]

Out of curiosity, what exactly does that command do? (Too scared to actually try it out)

[Steven Lord]

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.

Answer 3

[Jacob Halbrooks]

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

[Jos (10584)]

You (almost) never need eval ...

[Hoon]

God, both answers are great! How can i choose both?

[Stephen Cobeldick]

@Hoon: use Jos's answer. It is the better way of solving this problem.

Answer 4

[Iain]

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 = ’