My error is the ever popular ::::Error using fprintf Invalid file identifier. Use fopen to generate a valid file identifier. Error in pro1 (line 7) fprintf(fileID,'edges\t initial_nodes\t nodes_after_reduction\t difference \n')

if g == 1 
 
        fileID = fopen('output2\cycle_graph_output.txt','w')%Creates a output text file in folder output2
        fprintf(fileID,'edges\t initial_nodes\t nodes_after_reduction\t difference \n') 
        myfolderinfo = dir('cycle_graph') ; %lists folder contents   
        N = length(myfolderinfo) ; 
        

so the code is working perfectly when i'm using the Matlab in my local system.

But its generating the error when i tried to run it on Matlab online. What changes can i make to make it work on Matlab online

Answer 1

[Walter Roberson]

MATLAB Online does not use MS Windows; it uses Linux. The directory separator is / not \

MS Windows is happy to use / instead of \ so you should just change the \ to /

Better yet, use fullfile()

... And of course make sure you have a directory named output2 relative to where you are running the code.

[Nitish Reddy Kotkur]

f = fullfile('output2','cycle_graph_output.txt')
        fileID = fopen(f,'w')
        

It's still showing the same error

[Walter Roberson]

What shows up for

dinfo = dir('.');
dinfo(~[dinfo.isdir]) = [];
{dinfo.name}

!ls -ld output2

[Nitish Reddy Kotkur]

It is used to access various files in a folder

[Nitish Reddy Kotkur]

fileID = fopen('cycle_graph_output4.txt','w')%Creates a output text file

so i just removed the folder.so the above statement craetes a output text file.Its working fine in my local system.But when i try the same thing is Matlab online it is not creating a file,rather the it is displaying output as

file id= some value

[Steven Lord]

Call fopen with two outputs and show us both the output values that get displayed when you run that code in MATLAB Online.

[Walter Roberson]

fileID = fopen('cycle_graph_output4.txt','w')%Creates a output text file

would be expected to display a number as well as creating the output file. If the number is negative then file creation failed; if the number is positive then file creation worked.

On MATLAB online, what shows up if you execute this command:

!pwd; ls -ld .; whoami

Note that the ! at the beginning is part of the command.