Need to read data from text format to matlab

    function [von_s]=Read_ODB_outputs_node()
clear all
clc
close all
debug = 0;
if (debug)
    debug_file = fopen('debug.txt', 'wt');
end
%while exist ('out.txt','file')==0
    %pause(0.1)
%end
file = 'out.txt';
fidd = fopen(file);
i = 0;
pause(0.5)
numSteps = 0;
j=0;
von_S=zeros;
while ( ~feof(fidd) )
    
    tline = fgetl(fidd);
    
    i = i+1;
    if (regexpi(tline, '  ***** POST1 NODAL STRESS LISTING *****')>0) 
        numSteps = numSteps + 1;
        tline = fgetl(fidd);
        i = i+1;
        
        while(isempty(str2num(tline)))
            tline = fgetl(fidd);
            i = i+1;
        end
        while(~isempty(str2num(tline)))
            j=j+1;
            data_f = sscanf(tline, '%d %e %e %e %e %e ', [1,6]);
           if (debug)
                fprintf(debug_file, '%d\t%e\n', data_f(1), data_f(6));
           end
            node_number=data_f(1);
            tline = fgetl(fidd);
            i = i+1;
            von_S(j)=data_f(6);
            
        end
        if (debug)
            fprintf(debug_file, '\n');
        end
    end
end
if (debug)
    fclose(debug_file);
end
fclose(fidd);
fclose all

error is

Error using str2num (line 35)

Input must be a character vector or string scalar.

Error in Read_ODB_outputs_node (line 29)

while(isempty(str2num(tline)))

[POTTA SATEESH]

results are coming but still showing errors.....

need to read node amd SEQV values and use them for another code....please help

[Rik]

You should avoid str2num. Use str2double, textscan or sscanf instead.

I would also suggest not mixing the reading of a files with the processing of a file.

You can get my readfile function from the FEX. If you are using R2017a or later, you can also get it through the AddOn-manager. For R2020b and later you can also use readfile=@(varargin)cellstr(readlines(varargin{:})) (note that readlines has slightly different optional parameters).

Answer 1

[Clayton Gotberg]

I was able to reproduce your error as below:

A = str2num('') % An empty character vector; Result: A = []
B = str2num([]) % An empty matrix; Result: the error you got

The documentation for fgetl says that, after the last line of the file is reached, the result of the function is -1. Because this is already a number, you will not be able to transform it with str2num.

I notice that you are using feof to stop execution at the end of the text file. The issue is that you are using fgetl several times before MATLAB evaluates the while statement again.

while ( ~feof(fidd) )
    
    tline = fgetl(fidd); % First time it's used. 
    if %condition% 
        tline = fgetl(fidd); % Second time it's used.        
        while (isempty(str2num(tline)))
            tline = fgetl(fidd); % Third time it's used.
            i = i+1;
        end
        while(~isempty(str2num(tline)))
            j=j+1;
            %evaluation code
            tline = fgetl(fidd); % Other third time it's used.
            i = i+1;
            von_S(j)=data_f(6);
            
        end
        % debug code
    end
end

MATLAB only checks the condition of the while loop at the beginning of each new loop.

For example,

X = true;
while X==true
    X = false;
    X = true;
end

Will run forever because X is always true when MATLAB checks.

You either need to call one line each time the first while loop starts or you need to add stops in other parts of the code. For example, adding

if feof(fidd)
    break
end

in each of your while loops should stop the program from executing after the end of the text file is reached.

However, you may prefer to reorganize your code as follows:

while ( ~feof(fidd) ) % The program runs as long as there is more file to read.    
    tline = fgetl(fidd); % Get the next line of the program.
    if regexpi() % If the regexpi condition is met...
        i=i+1;
        if (~isempty(str2num(tline))) % If there is data in tline...
            j=j+1;
            %Code to evaluate the data in tline.
        end
    end
        % debug code
end

The program reads every line of the file (I have a hunch your previous program was skipping some lines) and then evaluates each one according to the same conditions as your program.

Finally, note that isempty gives the same results whether the array is numeric or characters. Because of this, there is no need for str2num in the conditions.

[POTTA SATEESH]

thank you so much ,sir

i tried sir, and debug code is also trimmed

still shownig error

 function [V_S]=ap()

file = 'out.txt';
fidd = fopen(file);
i = 0;
j = 0;
V_S=zeros;
while ( ~feof(fidd) ) % The program runs as long as there is more file to read.    
    tline = fgetl(fidd); % Get the next line of the program.
    if (regexpi(tline, '  ***** POST1 NODAL STRESS LISTING *****')>0)  
        i=i+1;
        if (~isempty(str2num(tline)))% .
            j=j+1;
            data_f = sscanf(tline, '%d %e %e %e %e %e ', [1,6]);
            fprintf('%d\t%e\n', data_f(1), data_f(6));
        end
            tline = fgetl(fidd);
            i = i+1;
            V_S(j)=data_f(6);        
    end
end
fclose(fidd);
fclose all

error:

>> ap

Unrecognized function or variable 'data_f'.

Error in ap (line 19)

V_S(j)=data_f(6);

[Clayton Gotberg]

Your new error is because you are asking for data_f before you define it. You only want to write over V_S when you get a non-empty line so why not move it into the second if statement?

[POTTA SATEESH]

thank you sir... tried sir, but it didn't worked .

can you help me to develop a proper code to extract (node and SEQV ) from text file by correcting above code...

im noob in matlab sir...

[Clayton Gotberg]

If you attach an example of the file you want the script to read, I can spend some time looking into it. Definitely look at @Rik's comment on this post as well. You will probably have a much easier time if you read the file into memory and then process it.

[Rigo ZOO]

Hi Dear Clayton,

I have similar issue to read a dat file, I tried to use your recommendations but unfortunately I still have the same error. Please can I share my script with you?

[Rik]

@Rigo ZOO Please post your question as a separate thread. Before that, have a read here and here. Don't forget to attach your file (rename it to .txt to be able to upload it here).

Feel free to post a comment here with a link once you have posted your question.