Failure of fopen for a text file I have full access upon

Hello,

Before highlighting my problem, I'm describing my code, and the problem is explained at the end of the request.

My program does the following :

1 - From a side program, I generate a text file containing data that I want to modify : so I open this text file using the following lines of codes.

Input = fopen(fullfile('C:\Users\Lucas\Desktop\MonDossier','inputdata.txt'));
if Input==-1
    error('Failed to open the file because: %s', message);
else
    tlineSP = fgetl(Input);
    tlinesSP = cell(0,1);
    while ischar(tlineSP)
        tlinesSP{end+1,1} = tlineSP;
        tlineSP = fgetl(Input);
    end
end
fclose(Input);

The entities tlineSP and tlinesSP are respectively cell and cell array of characters.

2 - Then I bring modifications to the text file mentioned above, by using a template of the lines I'm interested in and filling it with the values I'm modifying, like so :

for i=1:Etage 
%Lis les valeurs de poids/étage et les incrémente.
   ligne = '           %u    3000.000    %u.000'; 
   floor=char(tlinesSP(1167+i,1)); 
   Fpoids = str2double(floor(28:32));
   Fpoids = Fpoids + Increment;
   cellule = [i Fpoids];
   tlinesSP{1167+i,1}=sprintf(ligne, cellule(1), cellule(2));
   
%Modifie les 16 blocs de valeurs correspondant aux poids à chaque noeud.
   token = '      %u      %u     %u    %u';
   tlinesSP{1178+5*i} = sprintf(token, NouveauNoeud, NouveauNoeud*2, NouveauNoeud*2, NouveauNoeud);
   tlinesSP{1179+5*i} = sprintf(token, NouveauInter, NouveauInter*2, NouveauInter*2, NouveauInter);
   tlinesSP{1180+5*i} = sprintf(token, NouveauInter, NouveauInter*2, NouveauInter*2, NouveauInter);
   tlinesSP{1181+5*i} = sprintf(token, NouveauNoeud, NouveauNoeud*2, NouveauNoeud*2, NouveauNoeud);
   
end

So the idea is to get the values at their locations in the lines I'm focusing on, and then modify them in the cell array. NouveauInter and NouveauNoeud are both int64.

3 - And finally, I'm writing the cell array lines back into their origin text file, with this :

[Input, message] = fopen(fullfile('C:\Users\Lucas\Desktop\MonDossier','inputdata.txt'),'wt');
if Input==-1
    error('Failed to open the file because: %s', message); %This is line 119
else
    for i = 1:numel(tlinesSP)
        fprintf(Input,'%s\n', tlinesSP{i});
    end
end
fclose(Input);

After this I launch the side program with a command line, also written in this very code, which uses the text file inputdata.txt that I modified, and gives as a result output data that does not interfere with the rest of my code.

PROBLEM:

The whole code is looping with a while loop, and after one iteration of the loop, the program stops and I get the following message : Error using Pushdown (name of the program) (line 119) - Failed to open the file because : Permission denied.

The line mentioned here is the writing part of my program, highlighted by the comment 'This is line 119' on part 3 of my request.

Also note that I'm working on my personal space and that I am administrator and only physical user of my computer, I also checked the avaibality of the file and the folder it is contained in, and I have full access on it.

Looking forward your answers, and hoping it will help me solve the problem.

Best regards and in advance, thank you.

Lucas

[Walter Roberson]

I am not clear as to whether the side program might have the file open at the time that the fopen() with 'wt' is requested? If so then that could cause the problem, due to automatic file locking.

[Jan]

By the way, a simplification of your code to read the file:

tlinesSP = splitstr(fileread(FileName), char(10));

Maybe you have to char fo the old fashioned char([13,10]) line breaks then, because you prefer the text mode for writing files. Remember, that all editors can handle the char(10) as line break also, since even Microsoft decided to update the Notepad editor.

"The entities tlineSP and tlinesSP are respectively cell and cell array of characters." - tlineSP is a char vector, not a cell.

It is a bad idea to work with admin privileges. There is a risk to modify the toolbox functions of Matlab by accident and this is extremely hard to detect and to debug. Usually a re-installtion is the only way to fix this.

[Walter Roberson]

tlinesSP = regexp(fileread(FileName), '\r?\n', 'split')

can handle optional CR.

[Lucas Vincent]

Hello Jan, Hello Walter, and thanks for both of your answers and comments.

After examining your comments, you pointed that the side program I am using might leave my file locked and indeed in my code I call the command pannel like so :

status = system('cd C:\Users\Lucas\Desktop\MonDossier & Response.exe &');

My supervisor pointed that the "&" character maintains the process going still, and maybe this is where the conflict comes from. Also note that I execute this line after asking to write into my text file, in a while loop.

I would be happy to get your opinion on this before bringing anymore change.

Thanks,

Lucas

[Walter Roberson]

your supervisor is correct .

note the first & should be ; or else the cd might not be done in the same process as the executable .

Answer 1

[Jan]

The message is partially clear: "Failed to open the file because : Permission denied"

You cannot open the file for writing, but what is the missing "permission"? Usually this means, that the file is opened by Matlab or another program. You can use the free ProcessExplorer of SysInternals to check, which program locks the file.

You can check inside Matlab, if the file is still open:

OpenFID = fopen('all');
for k = 1:numel(OpenFID)
    [filename, permission] = fopen(OpenFID(k));
    fprintf('Open: %s [%s]\n', filename, permission);
end