how to solve the fopen error?

Question

Lilya 2017-8-17

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链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/353089-how-to-solve-the-fopen-error

评论： Lilya 2017-8-17

Hi all,

I've done the below code to read .txt files and extracting columns from each one. the error appears just from the second to the rest of files. Could anyone help me with this?

thank you

 Error using fgets
 Invalid file identifier. Use fopen to generate a valid file identifier.
 Error in RUV_readFile (line 21)
    line = fgets(file1);
 clc
 clear all
 close all
 %read file line by line 
 %loop over the files from list
 %open each file and loop over the lines, 
 files_str = fileread('foldername/files.txt');
 list = splitlines(files_str);
 for k=1:length(list)
    filename = list{k}; %index cell array of filenames using k 
    disp(filename);
    file1 = fopen(strcat('foldername',filename));
    filemat = [];
    line = fgets(file1);
    while ischar(line)
       if isempty(strfind(line,'%')) %if line doesn't contains %
           vec = str2num(line); %convert line string to vector
           filemat = [filemat;vec]; %fill matric from vectors in file
       end
 %        disp(line)
       line = fgets(file1);
    end
       fclose(file1);  
       cols = filemat(:,1:4);
       save(strcat('output/',filename), 'cols', '-ascii')
 end

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Stephen23 2017-8-17

编辑：Stephen23 2017-8-17

@Guillaume: thank you for the detailed explanation. It was remiss of me to not explain as much as you did.

@Lina Eyouni: you should read the MATLAB documentation, which shows just how simple this should be:

https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html

https://www.mathworks.com/help/matlab/import_export/ways-to-import-text-files.html

Lilya 2017-8-17

Thanks Guillaume I am applying this now but without the apostrophes, it gives me an error. but I am working now with reading it from the links above. the other thing that I would like to clarify is the folder name. the name above is just to show the case because mine here is too long. I apologize.

thank you once again

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Answer 1

Stephen23 2017-8-17

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/353089-how-to-solve-the-fopen-error#answer_278283

编辑：Stephen23 2017-8-17

在 MATLAB Online 中打开

Use fullfile instead of the rather inappropriate strcat.
Return the second output of fopen and check this using assert.

[file1,msg] = fopen(fullfile('foldername',filename));
assert(file1>=3,msg)

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Stephen23 2017-8-17

编辑：Stephen23 2017-8-17

在 MATLAB Online 中打开

Then you have no problem. If the first output is >=3 then fopen successfully opened the file.

Note that you should replace ischar:

while ischar(line)

with feof:

while ~feof(file1)

Also note that this:

    line = fgets(file1);
    while ischar(line)
       if isempty(strfind(line,'%')) %if line doesn't contains %
           vec = str2num(line); %convert line string to vector
           filemat = [filemat;vec]; %fill matric from vectors in file
       end
 %        disp(line)
       line = fgets(file1);
    end

is a very inefficient way to read numeric data into MATLAB. You have not described what format the files have, but you should really consider using the inbuilt functions for reading numeric data:

https://www.mathworks.com/help/matlab/standard-file-formats.html

Lilya 2017-8-17