MATLAB: I fread() 16 bit binary data perfectly, but doing an fwrite() of that same data into a new file produces problems

fwrite binary data

I have an input text file opened for reading. It contains a 1024 byte header and then a variable amount of 16 bit binary data. I read it as such:
      SynthesizedHeader = fread(InputFId,1024, 'char*1');
      [FieldData,DZTBytes] = fread(InputFId,[NumberOfRows, Inf], '*int16', 0, 'ieee-le');
So far, so good. The header is parsable, array dimensions and data types are correct, and the data plots as expected, so all is being read correctly. I make some minor adjustments to the information in the header but don't touch the FieldData at all.
I then want to take the data that I just read and put it into a newly created output file. The code that I've got is this:
      OutputFId = fopen( fullfile (OutputPath, OutputFileName),'wt');  % create a new output file
      fwrite ( OutputFId, SynthesizedHeader, 'char*1');
      fwrite ( OutputFId, FldData, 'int16', 0, 'ieee-le');
Here is the problem: while the first fwrite() results in a perfect header in the output file, there are too many data items written by the second fwrite(). (For example, I properly fread in 884736 bytes into the FieldData because it is a 512 x 864 array of int16s; but I fwrite out 894290 bytes as demonstrated by both ftell() and the size of the output file on disk.)
This problem happens even if I comment out the first fwrite() or reshape the data matrix to be one dimensional- clearly I'm doing something wrong with the format of the second fwrite(), but cannot determine what that may be.
Many thanks in advance for identifying my mistake!

Best Answer

When you use fwrite() you should avoid opening the file with 't' access. 't' requests translation of linefeed to carriage-return + linefeed pairs. Use 'w' in the fopen not 'wt'
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