How to address: Invalid file identifier. Use fopen to generate a valid file identifier?

Hello,

I am trying to run the following lines but it shows error.

fid = fopen('/dev/tty', 'r');
% Display program information
fprintf(fid, '\nDetails of the program.\n');

Error using fprintf
Invalid file identifier. Use fopen to generate a valid file identifier.

I googled answer for it and understood that since fid is -1, I cannot write. But, I do not know how to solve this issue.

Any help is greatly appriciated.

Answer 1

[KALYAN ACHARJYA]

fid = fopen('/dev/tty', 'r');  
if fid == -1
    error('Failed to open /dev/tty for writing.');
end
fprintf(fid, 'Details of the program.\n')

#else

% Open for writing (r for reading)
fid = fopen('/dev/tty', 'w');  

[Walter Roberson]

device = '/dev/tty';
if ~exist(device, 'file')
    error('no file "%s"', device);
else
    [fid, msg] = fopen(device, 'a+');  
    if fid == -1
        error('Failed to open "%s" because: "%s"', device, msg);
    end
end