'fopen' function error when placed inside of user defined function

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Harry Carr
Harry Carr 2015-9-19
评论： Image Analyst 2015-9-19
I am currently doing a question which requires me to write a function that has a file as the function input. The functions task is simply to open any file required containing just numbers and display it as a matrix. As I understand it, I can do this using the fopen and fscanf functions. This works fine, however when I try implement it as a function, I run into an error. This is what I have, first without it being inside my user function, which works, and second with it being inside my user created function which does not:
%#1
fid = fopen('1.txt');
x = fscanf(fid, '%f\n', [13, inf]);
%#2
function x = fun(file_name)
fid = fopen(file_name);
x = fscanf(fid, '%d\n', [13, inf]);
#2 Returns the error:
Error using fscanf
Invalid file identifier. Use fopen to generate a valid file identifier.
Error in fun (line 3)
x = fscanf(fid, '%f\n', [13, inf]);
I'm really not sure how to fix this and any help would be much appreciated. (also I have included and if statement for if the file cannot be found but with or without this I still get the above error)
  2 个评论
Image Analyst
Image Analyst 2015-9-19
Can you attach the text file, or at least the first few lines of it as a file with the paperclip icon?

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采纳的回答

Star Strider
Star Strider 2015-9-19
编辑：Star Strider 2015-9-19
You don’t say how you call your function in your main program, and that would be useful to know. Your ‘file_name’ variable you send as a function argument has to be a string.
For instance:
file_name = '1.txt';
x = fun(file_name);
should work, assuming text file 1.txt exists in your MATLAB search path.
EDIT — Also consider adding the 'r+' permission:
fid = fopen(file_name, 'r+');
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显示 1更早的评论
Star Strider
Star Strider 2015-9-19
My pleasure!
Believe me, we’ve likely all done the same (I know I have), so you’re in quite good company!
Image Analyst
Image Analyst 2015-9-19
Don't quit with just that fix. It would still be a good idea to put in the more robust coding practices like I suggested, especially if you're going to write code that others will run without you being present.

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更多回答（1 个）

Image Analyst
Image Analyst 2015-9-19
Try this more robust code for your function:
if exist(file_name)
fid = fopen(file_name, 'rt');
if fid ~= -1
x = fscanf(fid, '%d\n', [13, inf]);
fclose(fid);
else
message = sprintf('Unable to open file for reading:\n%s\nPerhaps it is locked by another process.', file_Name);
uiwait(warndlg(message));
end
else
message = sprintf('File not found:\n%s', file_Name);
uiwait(warndlg(message));
end

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