Matlab Doesn't Recognize Fits Files (evalin, sprintf)?

I need my script to read in five images (capture_667.fit... capture_671.fit), and name them image667... image 671. I have the following code:

for j = 667:671
    evalin('base', sprintf('[ image%03d ] = fitsread(capture_%03d.fit);', j, j));
end

However, I get this error message:

.

'Undefined variable "capture_667" or class "capture_667.fit".

Error in Try_Sprintf_Evalin_New (line 5) evalin('base', sprintf('image%03d = fitsread(capture_%03d.fit);', j, j));'

.

All of the files I'm trying to read in are in the right folder. Furthermore, if I try to open these files manually, I get this message:

.

'Error using open (line 162) CFITSIO library error (412); datatype conversion overflow'

.

What's stopping my code from working? And what is a datatype overflow? I've looked online for a definition but with no luck.

NB: This task was set by demonstrators at university. I HAVE to complete it using sprintf, evalin, and fitsread.

Answer 1

[Thorsten]

You forgot to put the image name into quotation marks to mark them as strings; note that you have to use two because they appear inside quotation marks:

 evalin('base', sprintf('image%03d = fitsread(''capture_%03d.fit'');', j, j));

A better way would be without evalin

for j =  667:671
  filename = sprintf('capture_%03d.fit', j);
  I{j} = fitsread(filename);
end

You can then work with I{667}, for example. One drawback of the evalin approach is that it is more error prone (you've just made the experience).

[MC]

It works! Thank you so much! I wasn't aware of the double-' part: I'd tried with single and when I noticed that it "ended" the string, I thought I couldn't use any.

Answer 2

[Walter Roberson]

If you need your code to do that, then it is time to renegotiate the requirements with who-ever imposed that constraint. Creating variables on the fly is not recommended at all.

http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F

[MC]

It's part of a lab for uni, so I have to do this using sprintf, fitsread, and evalin. If the files are to be read in, I need to assign them names for when they enter the workspace.

[Walter Roberson]

Well now you begin to see why we do not recommend using eval() or evalin() .

Is the requirement definitely for evalin()? You cannot use assignin() instead?

[MC]

Definitely evalin. This task also requires me to use sprintf and fitsread.

Answer 3

[Stephen23]

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

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