MATLAB: Does FREAD read the data incorrectly when using the ‘char’ format specification with MATLAB 7.3 (R2006b) on Linux

charfreadlinuxMATLABskipunix

When I use the following command on Windows with MATLAB 7.3 (R2006b):

a=fread(fopen('test'),64,'char')';
size(a)

I obtain

 ans =
      1    64

On Linux I obtain:

 ans =
      1    62

'schar' and 'uchar' format specification give me the same answer with FREAD on every platforms.

Best Answer

'char' to FREAD means "read a character in the local codepage". The local codepage is different on Windows and Linux, so that is why there are different results between OSes. To read unsigned bytes and not characters, the correct precision specification is 'uint8' (which is the same as 'uchar').

Related Solutions

MATLAB: Are some bytes skipped from input when I try to use FREAD function to read a file that is opened in ‘rt’ mode on Windows platforms in MATLAB 7.11 (R2010b)

This behavior is observed on Windows platforms when you read a file in text mode using the 'rt' option in FOPEN. The following applies on Windows systems, in text mode:

- Read operations that encounter a carriage return followed by a newline character ('\r\n' or 0D 0A in Hex) remove the carriage return from the input.

- Write operations insert a carriage return before any newline character in the output.

Please refer to the documentation of FOPEN function for more information:

 <http://www.mathworks.com/access/helpdesk/help/techdoc/ref/fopen.html>

MATLAB: ‘fwrite’ does not write ‘char’ variables in binary files

Hi,

I'm not really sure if this is not working as it should. If you do the following:

fid = fopen('foo.bin', 'wb');
fwrite(fid, 'hello', 'uchar');
fclose(fid)

you will have a file created with 5 bytes. The return argument of fwrite may be double, but it only tells you that you wrote 5 bytes, not the content.

Now for the reading: if you want to have 5 bytes (and not 5 characters with 2 bytes each) do the following:

fid = fopen('foo.bin', 'rb');
s = fread(fid, '*uchar')';
str = char(s) % you indeed read the hello from above
whos s % will have uint8, i.e., the ascii code
fclose(fid);

Titus

Best Answer

Related Solutions

MATLAB: Are some bytes skipped from input when I try to use FREAD function to read a file that is opened in ‘rt’ mode on Windows platforms in MATLAB 7.11 (R2010b)

MATLAB: ‘fwrite’ does not write ‘char’ variables in binary files

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