MATLAB: Append data at the beginning of a file MATLAB
append file write
Hi, please how can fopen be used to append data at the beginning of the file ? like a header.
thank-you
Best Answer
You cannot insert characters in front of a file directly. This is a limitation of the file systems and not a problem of Matlab and not a task for FOPEN. So you have to read the complete file at first, add the new characters in the memory and (over)write a new file:
S = fileread(FileName);
S = ['Your header line', char(10), S];
FID = fopen(FileName, 'w');
if FID == -1, error('Cannot open file %s', FileName); end
fwrite(FID, S, 'char');
fclose(FID);
There should be an equivalent process using a memory mapped file. I'm not sure if internally exactly the same is performed, such that there is no difference is the speed. But I assume if the files contains several GigaBytes, the memory mapped method should be better.
Did you open the file with 'rt' instead of 'r' in order to account for the CRLF ?
Also note that if you use a count for textscan() then the file position will be left after the last format code is used,before the newline for that line (unless the end of format matches newline)
Best Answer