fopen does not open a file correctly

I'm trying to implement in my code some code written by someone else but i'm having problem with the "fopen" function as it doesnt open correctly the file even if the path is correct.

I should add that all these files are in the same directory which contains the subdirectories .mpropep (after it is created), cpropep, io, gasdynamics and num. The function mpropepWriteInput.m is saved inside io

(I'm really sorry if i include more code than necessary but i'm new to this)

my main code is:

addpath("cpropep")
addpath("io")
addpath("gasdynamics")
addpath("num")

pressure=5e05; %TEST VALUE
expansionRatio=2; %TEST VALUE

mpropepPath = pwd; % mpropep initialization
mkdir .mpropep;

%I included some checks
if exist('.mpropep', 'dir') ~= 7
    error(' Failed to create .mpropep folder. Check permissions.');
else
    disp(' .mpropep folder created successfully.');
end

fid = fopen(fullfile(mpropepPath, '.mpropep', 'test.txt'), 'w');
if fid == -1
    error(' Cannot create file. Check permissions.');
else
    fprintf(fid, 'Test file created successfully.\n');
    fclose(fid);
    disp(' File written successfully.');
end
%end of checks

oxidantID = 657; % Dinitrogen monoxide
fuelID = 1032; % Paraffin
OFRatio = 7;
listPropellantID = [oxidantID fuelID];
listMass = [OFRatio 1];
mpropepWriteInput(listPropellantID, listMass, 'EQ_AR', pressure, expansionRatio, '')
runComputation('', '', mpropepPath);
output = readOutputFile('');
characteristicVelocity = getParamFromOutput(propellantNumber, 'c*', 'EQ_AR', output);

    

the part in the function mpropepWriteInput that is giving me problems is:

function [] = mpropepWriteInput( ...
                                listPropellantID, ...
                                listPropellantMass, ...
                                solver, ...
                                solverArg1, ...
                                solverArg2, ...
                                path)
    % Number of components in the simulation
    n = length(listPropellantID);
    
    % Check that components are enough
    if n < 2
        error('Components must be at least two. Insert component twice if alone.')
    end
    
    % Check that lists are same size
    if length(listPropellantID) ~= length(listPropellantMass)
        error('Number of IDs and masses does not match')
    end
    ciao1=1; %this is just a flag I included to check where code was going
    disp(ciao1);
    % Open input file
    fileattrib('.mpropep', '+w');  % Grant write permissions

    ciao2=2;
    disp(ciao2);
    if ~exist("path","var")
        inputFile = fopen('.mpropep/input.txt','w');
        ciao3=31;
        disp(ciao3);
    else
        inputFile = fopen(path,'w');
        ciao3=32;
        disp(ciao3);
    end
    ciao4=4;
    disp(ciao4);
    disp(inputFile);
    ciao5=5;
    disp(ciao5);

    % Premise
    fprintf(inputFile,'### AUTOMATICALLY GENERATED: EDIT AT OWN RISK ###\n');
    time = clock;
    fprintf(inputFile,'## run on %i/%i/%i  %i:%i:%i\n\n',time(1),time(2),time(3),time(4),time(5),round(time(6)));

the problem that I when I run the code I get:

Warning: Directory already exists.

> In Altitude_1D_Sounding_Rocket (line 42)

.mpropep folder created successfully.

File written successfully.

1

2

32

4

-1

5

Error using fprintf

Invalid file identifier. Use fopen to generate a valid file identifier.

Error in mpropepWriteInput (line 89)

fprintf(inputFile,'### AUTOMATICALLY GENERATED: EDIT AT OWN RISK ###\n');

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Error in Altitude_1D_Sounding_Rocket (line 64)

mpropepWriteInput(listPropellantID, listMass, 'EQ_AR', pressure, expansionRatio, '')

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Answer 1

[Walter Roberson]

You should be using

    if ~exist("path","var")
        infilename = '.mpropep/input.txt';
        [inputFile, msg] = fopen(infilename,'w');
        if inputFile < 1
            error('failed to open "%s" for writing because "%s"', infilename, msg);
        end
        ciao3=31;
        disp(ciao3);
    else
        [inputFile, msg] = fopen(path,'w');
        if inputFile < 1
            error('failed to open "%s" for writing because "%s"', path, msg);
        end        
        ciao3=32;
        disp(ciao3);
    end

Note that using a variable named path is not the best idea, as doing so interferes with the path() function call.

[Alessandro]

I get a similar error:

Warning: Directory already exists.

> In Altitude_1D_Sounding_Rocket (line 42)

.mpropep folder created successfully.

File written successfully.

ciao1

ciao2

Error using mpropepWriteInput (line 94)

failed to open "" for writing because "Cannot open file. Existence? Permissions? Memory? . . ."

Error in Altitude_1D_Sounding_Rocket (line 64)

mpropepWriteInput(listPropellantID, listMass, 'EQ_AR', pressure, expansionRatio, '')

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[Alessandro]

Thank you for the help.

The code might be redundant but the problem was solved like this:

% Open input file
if ~exist('inputPath', 'var') || isempty(inputPath)
    inputPath = fullfile('.mpropep', 'input.txt'); % Default inputPath
end
fileattrib('.mpropep', '+w');  % Grant write permissions
if isempty(inputPath)
    error('inputPath is empty. Please specify a valid file path.');
end
if ~exist("inputPath","var")
    infilename = '.mpropep/input.txt';
    [inputFile, msg] = fopen(infilename,'w');
    if inputFile < 1
        error('failed to open "%s" for writing because "%s"', infilename, msg);
    end
else
    [inputFile, msg] = fopen(inputPath,'w');
    if inputFile < 1
        error('failed to open "%s" for writing because "%s"', inputPath, msg);
    end
    
end

[Walter Roberson]

You have several conditions that are redundant. You can simplify to:

outputpath = '.mpropep';
if ~isdir(outputpath)
    mkdir(outputpath);
end
fileattrib(outputpath, '+w');  % Grant write permissions

% Open input file
if ~exist('inputPath', 'var') || isempty(inputPath)
    inputPath = fullfile(outputpath, 'input.txt'); % Default inputPath
end

[inputFile, msg] = fopen(inputPath,'w');
if inputFile < 0
    error('failed to open "%s" for writing because "%s"', inputPath, msg);
end

[Alessandro]

thank you