MATLAB: Error in Reading and Writing a text file

read data

I have a problem with my program when i read and write the file. The following code is what I have so far. It works when I use only textscan and fopen with 'r' instead of 'r+'. The error is Invalid file identifier, Use fopen to generate a valid file identifier. Can somebody see a mistake? Thank you in advance
fid = fopen('3.csv', 'r+'); %Opens the file
NData = textscan(fid, '%s %s %d % ... %d', 'delimiter' ,',',         'headerlines',2); 
T_DB = NData {32};  %Gets Dry Bullb Temperature
T_DP = NData {35}; %Gets Dew Point Temperature
RH = NData {38}; %Gets Relative Humitidy
Temp_data = [T_DB T_DP RH]; 
frewind(fid)
fprintf(fid, '%f %f %f', Temp_data);
fclose(fid); %Closes the file

Best Answer

While "fopen(FileName, 'r')" searchs the file in all folders of the Matlab path, "fopen(FileName, 'r+')" looks in the current folder only. To solve this, change into the folder, which contains the file (see CD) or specify the file by a full path (see FULLFILE).
As a side-effect the fopen with 'r+' is about 2.3 times faster than with 'r' even if the file is specified with a full path.
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