How to get the final number of lines in a data file?

Question

smo 2015-8-20

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/234746-how-to-get-the-final-number-of-lines-in-a-data-file

评论： smo 2015-8-20

Hi all, I have a data file as follow:

x 0 y 1
x 1.3 y 2.2
x 2.2 y 6
x 3.4 y 7.4

I need to read into this file, plot the data (which is done) and put the number of lines in the title of the plot. I uses the following code to get the number of lines:

count = 0;
while ~feof(fid)
   count = count+1
end

however, as it is in a while-loop, the 'count' changes every time:

count =
     1
count =
     2
count =
     3
count =
     4

how to get a FINAL number of lines ? (aka, I want count = 4 and only =4, not varying during each time the loop running). as I need to put this 'final' number into title.

Thank you very much.

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Answer 1

Walter Roberson 2015-8-20

2
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/234746-how-to-get-the-final-number-of-lines-in-a-data-file#answer_189827

在 MATLAB Online 中打开

count = 0;
while true
  if ~ischar( fgetl(fid) ); break; end
  count = count + 1;
end
fclose(fid)
title(sprintf('lines in file = %d', count));

Note that feof(fid) never predicts end of file. feof() is never true unless you have already tried to read after the end of file, so even with a completely empty file, feof() would not immediately be true.

You can tell you have reached end of file when fgetl() returns something that is not a character.

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smo 2015-8-20

在 MATLAB Online 中打开

hi, thanks for your help.

I have a further question: without 'while ~feof(fid)', i cannot run the codes to read the file and plot. I have attached my whole script here, could you please tell me how to modify it to make it run successfully? thank you.

fid = fopen ('data_chp11exe2.dat');
if fid == -1
    disp('File open not successful')
else 
    x = [];
    y = [];
    count = 0;
      while ~feof(fid)
      %following codes are to separate x and y values
      % then use them to plot 
              aline = fgetl(fid);
              aline = aline(3:length(aline));
              [x_val, rest] = strtok(aline);
              x_val = str2double(x_val);
              [y_name, y_val] = strtok(rest);
              y_val = strtrim(y_val);
              y_val = str2double(y_val) ;           
              x = [x, x_val];
              y = [y, y_val];
              count = count+1;
              area(x, y);
              xlabel('x');
              ylabel('y');
              title(sprintf('number of lines:%d', count));
       end
       fclose(fid)
  end

Walter Roberson 2015-8-20

在 MATLAB Online 中打开

fid = fopen ('data_chp11exe2.dat');
if fid == -1
    disp('File open not successful')
else 
    x = [];
    y = [];
    count = 0;
        while true
        %following codes are to separate x and y values
        % then use them to plot 
                aline = fgetl(fid);
                if ~ischar(aline); break; end
                aline = aline(3:length(aline));
                [x_val, rest] = strtok(aline);
                x_val = str2double(x_val);
                [y_name, y_val] = strtok(rest);
                y_val = strtrim(y_val);
                y_val = str2double(y_val) ;           
                x = [x, x_val];
                y = [y, y_val];
                count = count+1;
         end
         fclose(fid);
         area(x, y);
         xlabel('x');
         ylabel('y');
         title(sprintf('number of lines:%d', count));
end

smo 2015-8-20

Thank you so much.

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How to get the final number of lines in a data file?

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