MATLAB GUI error when filling textboxes with data from file

I am writing a MATLAB GUI program where the data put in a textbox is stored in a .dat file. When the program is reloaded, the textboxes fetch the data from the file (so that the user doesn't have to re-input his info every time). This part of the code saves the data to a .dat file:

 fid = fopen('textboxdata.dat', 'wt');
 fprintf(fid, '%s\n', host);
 fprintf(fid, '%s\n', username);
 fprintf(fid, '%s\n', password);
 fclose(fid);

[host, username, and password are strings]

This part of the code fetches the data and puts in into the text boxes:

 s = dir('textboxdata.dat');

 if s.bytes ~= 0
     fid = fopen('textboxdata.dat', 'rt');
     A = textscan(fid, '%s', 3);
     A = A{1};

     set(handles.hostbox, 'String', A(1))
     set(handles.usernamebox, 'String', A(2))
     set(handles.passwordbox, 'String', A(3))

     fclose(fid); 
 end

Now this works fine, but when the user tries to use this data to log onto an FTP server, I get this error:

??? Error using ==> fprintf Function is not defined for 'cell' inputs.

Error in ==> realgui>logonbutton_Callback at 198 fprintf(fid, '%s\n', host);

Error in ==> gui_mainfcn at 96 feval(varargin{:});

Error in ==> realgui at 42 gui_mainfcn(gui_State, varargin{:});

Error in ==> @(hObject,eventdata)realgui('logonbutton_Callback',hObject,eventdata,guidata(hObject))

But weirdly enough, if you retype all the data, you can log onto the FTP server just fine! I am thoroughly lost here. Does anyone have a clue what is happening?

Answer 1

[Matt Tearle]

Try using cell indexing in these lines:

set(handles.hostbox, 'String', A(1))
set(handles.usernamebox, 'String', A(2))
set(handles.passwordbox, 'String', A(3))

That is, change to:

set(handles.hostbox, 'String', A{1})
set(handles.usernamebox, 'String', A{2})
set(handles.passwordbox, 'String', A{3})

My guess as to what's happening is: A is holding cell arrays of strings (even though it's just one string in each cell), so the String property of your edit boxes is holding a cell array, rather than a string (char array). So when you go to print the contents, fprintf is freaking out (cell array input rather than a string). Does that make sense?

[Jack]

Worked like a charm...thank you so much Matt!