Open multiple files with fopen

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Giorgos Papakonstantinou
评论： Stephen23 2020-4-17
I have written two codes in matlab:
The first one is:
files=dir('*.csv');
for i=1:length(files)
fid(i)=fopen(files(i).name);
files(i).values=textscan(fid(i), '%f %f','delimiter',',','HeaderLines',20,'MultipleDelimsAsOne',1);
end
and the second one is:
str='C:\Users\user\Measurements\Test';
folder_name=uigetdir(str);
files=dir(fullfile(folder_name,'*.csv'));
for i=1:length(files)
fid(i)=fopen(files(i).name);
files(i).values=textscan(fid(i), '%f %f','delimiter',',','HeaderLines',20,'MultipleDelimsAsOne',1);
end
The first code is saved in the same folder as the files that I want to open. The second code is saved outside the folder where the files are stored. But both should read the same files. In the first code the structure files.values is composed by a 1x2 cell. Both cells contain a column vector with numerical values The problem arises in the second code which sometimes gives me an error because fid=-1 or the column vectors in the structure files.values are empty.
How can I overcome this problem?

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回答（3 个）

Walter Roberson
Walter Roberson 2013-4-26
Is there a reason to keep the fid's around? Often you would fclose() right after the textscan. This can be important in preventing you from running out of files.
When you do the fopen() ask for the message output. Then test the fid and if it is -1, display the message (and the file name.)
Giorgos Papakonstantinou
编辑：Giorgos Papakonstantinou 2013-4-26
Ok I corrected and I included the fclose() but I still get empty cells in the structure files.values. Why is that?
And also when I requested for a message I got this:
No such file or directory
which I can not explain it since the folder contains *.csv files and the folder exists since I use the uigetdir and I select the folder from the browser myself.
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Kostas Chatzimpaloglou
Kostas Chatzimpaloglou 2020-4-16
have found a solution to this problem?
Walter Roberson
Walter Roberson 2020-4-16
[fid(i),msg]=fopen(files(i).name);
should be
[fid(i),msg]=fopen( fullfile(folder_name, files(i).name));

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Giorgos Papakonstantinou
Ok solved myself. The problem was that I was using textscan outside the current folder. Therefore I changed the folder to the folder of interest and back to the initial folder.
str='C:\Users\user\Measurements\Test';
folder_name=uigetdir(str);
files=dir(fullfile(folder_name,'*.csv'));
curr_folder=pwd;
cd(folder_name);
for i=1:length(files)
[fid(i),msg]=fopen(files(i).name);
disp(msg);
files(i).values=textscan(fid(i), '%f %f','delimiter',',',...
'Headerlines',20,...
'MultipleDelimsAsOne',1);
fclose(fid(i));
end
cd(curr_folder)
  1 个评论
Stephen23
Stephen23 2020-4-17
Using cd should be avoided in code.
Using absolute/relative filenames is more efficient, robust, simple, and easier to debug, e.g.:
D = 'C:\Users\user\Measurements\Test';
S = dir(fullfile(D,'*.csv'));
for k = 1:numel(S)
F = fullfile(D,S(k).name);
[fid,msg] = fopen(F,'rt');
assert(fid>=3,msg)
S(k).values = textscan(fid,...);
fclose(fid);
end

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