Invalid file identifier. Use fopen to generate a valid file identifier.

Question

Pranav Thiagarajan on 21 Nov 2016

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https://se.mathworks.com/matlabcentral/answers/313241-invalid-file-identifier-use-fopen-to-generate-a-valid-file-identifier

Edited: Justin Bryant on 23 Feb 2023

Hello,

I am trying to open a file, skip the first 6 lines (headers) and extract data from the rest of the lines in the file. Here is the code:

%%Declarations
targetinfo(1000)=struct('distance', 0, 'speed', 0, 'angle', 0, 'rcs', 0);
i=1;                    %index
count=0;                %file size counter
[fid, message]=fopen('log.asc','r');   %open log file
%%Read file and extract relevant data
if fid==-1
    disp('Error')
else
    for k=1:6
        header=fgetl(fid);             %skip headers
    end
    while ~feof(fid)
        line=fgetl(fid);
        if line(16)=='S' || line(13)=='C' || line(1)=='T'       %remove control and status signals
            continue;
        end
        id=str2num(line(16:18));
        line=line(41:63);
        line=line(~isspace(line));
        if id==100
            canstatus=hex2dec(line(1:2));
            targetcount=hex2dec(line(3:4));
            canchannel=hex2dec(line(9:10));
        else
            targetinfo(i).distance=hex2dec(line(1:4));
            targetinfo(i).speed=hex2dec(line(5:8));
            targetinfo(i).angle=hex2dec(line(9:12));
            targetinfo(i).rcs=hex2dec(line(13:16));
        end
        count=count+1;                              %increase file size counter
        i=i+1;                                      %increase index
        fclose(fid);                                %close file
    end
end

I am getting the error I have specified in the title. The value of fid returned is not -1 (it is 4 at the moment) and I do have access to the file, since I can open it in Notepad to view its contents.

I am not opening and closing the file multiple times, just once. Is there any reason I'm missing out?

Thank you for your help.