How to output data to file in matlab?

Question

I've read several articles about how to output data to file, but it just doesnt seem to work for me. I have output.txt file at the same folder as my matlab file resides and it just doesn't output any data to that file?

What is wrong with it? I want to output coordinates as you click on image, so all output logic is in the listener.

function main 
    clc; close all;
    % set the range of the axes
    % The image will be stretched to this.
    min_x = 0;
    max_x = 1;
    min_y = 0;
    max_y = 1;

    % replace with an image of your choice
    img = imread('ryklys.jpg');

    imagesc([min_x max_x], [min_y max_y], flipud(img));
    hold on;
    colormap(gray);

    set(gca,'ydir','normal')

    cursor_handle = plot(0,0,'r+ ','visible','off')

    % now attach the function to the axes
    set(gca,'ButtonDownFcn', @mouseclick_callback)

    % and we also have to attach the function to the children, in this
    % case that is the line in the axes.
    set(get(gca,'Children'),'ButtonDownFcn', @mouseclick_callback)



   function mouseclick_callback(gcbo,eventdata)
      % the arguments are not important here, they are simply required for
      % a callback function. we don't even use them in the function,
      % but Matlab will provide them to our function, we we have to
      % include them.
      %
      % first we get the point that was clicked on
      cP = get(gca,'Currentpoint');
      x = cP(1,1);
      y = cP(1,2);
      % Now we find out which mouse button was clicked, and whether a
      % keyboard modifier was used, e.g. shift or ctrl
      switch get(gcf,'SelectionType')
          case 'normal' % Click left mouse button.
              s = sprintf('left: (%1.4g, %1.4g) level = %1.4g',x,y, x.*exp(-x.^2-y.^2));
          case 'alt'    % Control - click left mouse button or click right mouse button.
              s = sprintf('right: (%1.4g, %1.4g level = %1.4g)',x,y, x.*exp(-x.^2-y.^2));
          case 'extend' % Shift - click left mouse button or click both left and right mouse buttons.
              s = sprintf('2-click: (%1.4g, %1.4g level = %1.4g)',x,y, x.*exp(-x.^2-y.^2));
          case 'open'   % Double-click any mouse button.
              s = sprintf('double click: (%1.4g, %1.4g) level = %1.4g',x,y, x.*exp(-x.^2-y.^2));
      end
      % get and set title handle
      thandle = get(gca,'Title');
      set(thandle,'String',s);
      % finally change the position of our red plus, and make it
      % visible.
      set(cursor_handle,'Xdata',x,'Ydata',y,'visible','on')

      % append file with coordinates
      plot(x,y,'r.','MarkerSize',20);

      % Output to file 
        fid=fopen('output.txt','w');
        fprintf(fid, '%4.2f %4.2f \n', x, y);
        fclose(fid);
  end
end

This project is about how to get coordinates on image mouse click and to output point coordinates to file.

Answer 1

When first time launching this file, be sure to select "change folder" instead of "adding file to path". When I selected "change folder" Matlab was able to write data in the 'output.txt' file. Also, as Dev-iL suggested I added append mode, final code looks like this

function main 
    clc; close all;
    % Total points counter 
    counter = 0;

    % set the range of the axes
    % The image will be stretched to this.
    min_x = 0;
    max_x = 1;
    min_y = 0;
    max_y = 1;

    % replace with an image of your choice
    img = imread('ryklys.jpg');

    imagesc([min_x max_x], [min_y max_y], flipud(img));
    hold on;
    colormap(gray);

    set(gca,'ydir','normal')

    cursor_handle = plot(0,0,'r+ ','visible','off')

    % now attach the function to the axes
    set(gca,'ButtonDownFcn', @mouseclick_callback)

    % and we also have to attach the function to the children, in this
    % case that is the line in the axes.
    set(get(gca,'Children'),'ButtonDownFcn', @mouseclick_callback)

%     % Output to file 
    outputFile = 'output.txt';
    fid=fopen(outputFile,'wt');
    fclose(fid);

   function mouseclick_callback(gcbo,eventdata)
      % the arguments are not important here, they are simply required for
      % a callback function. we don't even use them in the function,
      % but Matlab will provide them to our function, we we have to
      % include them.
      %
      % first we get the point that was clicked on
      cP = get(gca,'Currentpoint');
      x = cP(1,1);
      y = cP(1,2);
      % Now we find out which mouse button was clicked, and whether a
      % keyboard modifier was used, e.g. shift or ctrl
      switch get(gcf,'SelectionType')
          case 'normal' % Click left mouse button.
              s = sprintf('left: (%1.4g, %1.4g) level = %1.4g',x,y, x.*exp(-x.^2-y.^2));
          case 'alt'    % Control - click left mouse button or click right mouse button.
              s = sprintf('right: (%1.4g, %1.4g level = %1.4g)',x,y, x.*exp(-x.^2-y.^2));
          case 'extend' % Shift - click left mouse button or click both left and right mouse buttons.
              s = sprintf('2-click: (%1.4g, %1.4g level = %1.4g)',x,y, x.*exp(-x.^2-y.^2));
          case 'open'   % Double-click any mouse button.
              s = sprintf('double click: (%1.4g, %1.4g) level = %1.4g',x,y, x.*exp(-x.^2-y.^2));
      end
      % get and set title handle
      thandle = get(gca,'Title');
      set(thandle,'String',s);
      % finally change the position of our red plus, and make it
      % visible.
      set(cursor_handle,'Xdata',x,'Ydata',y,'visible','on')

      % append file with coordinates
      plot(x,y,'r.','MarkerSize',20);

      % Increasing counter value
      counter = counter + 1;
      % Printing out points counter value
      text(x,y, strcat('#', int2str(counter)), 'color', 'r');

      % Output to file 
      fid=fopen(outputFile,'at');
      fprintf(fid, '%f %f %s %d\n', x, y, '; %', counter);
      fclose(fid);
  end
end