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problem with code

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Tor Fredrik Hove
Tor Fredrik Hove 2011-10-22
I am trying a script that does not work. First I define a structure in matlab:
>> package=struct('item_no',123,'cost',19.99,'price',39.95,'code','g')
package =
item_no: 123
cost: 19.9900
price: 39.9500
code: 'g'
then I have made a script who will try to find out the value of a field in the structure:
inputfield=input('Which field would you like to see: ','s')
if isfield(package, inputfield)
fprintf('The value of the %s field is: %c\n',inputfield,...
eval(['package.'inputfield]))
else
fprintf('Error: %s is not valid field\n', inputfield)
end
but i get error message:
>> structurevalue ??? Error: File: structurevalue.m Line: 6 Column: 22 Unexpected MATLAB expression.

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采纳的回答

Mitch Martelli
Mitch Martelli 2011-10-22
the problem is in the eval,try to put a blank after 'package.' :
eval(['package.' inputfield])
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显示 3更早的评论
Tor Fredrik Hove
Tor Fredrik Hove 2011-10-22
Hi Image Analyst! I am a bit new with matlab so convenient choices is not my strong side. Eval is also a part of the curriculum so I have to know something about it either way
Jan
Jan 2011-10-22
I do not understand what "is part of the curriculum" means. Using EVAL is a bad programming practize, because it is prone to errors and results in slow code.
"package.(inputfield)" is much safer and faster than "eval(['package.' inputfield])".

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更多回答（1 个）

Image Analyst
Image Analyst 2011-10-22
This is what the line should look like:
fprintf('The value of the %s field is: %c\n',inputfield, package.(inputfield));
Look up "dynamic field names" in the help for more info.
  1 个评论
Jan
Jan 2011-10-22
+1: Best answer. Perhaps ignoring your answers is a running joke. However, I'm missing the punchline.

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