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'fwrite' does not write 'char' variables in binary files

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blenis22 on 18 Mar 2019
Edited: blenis22 on 24 Mar 2019
I am reading a binary phase space file (* .egsphsp #), for simulations monteCarlo with EGSnrc.
My problem is in the file header. The floating variables read them in 1 byte with fread, however, the characters are read in 2 bytes, which causes problems when I generate my own phase space file, since fwrite writes the characters in 1 byte and as double.
Part of my codes:
fprintf ('Reading phase space file ... \ n')
MODE_RW = setstr (fread (fid, 5, 'uchar')) '; % Mode
NPPHSP = fread (fid, 1, 'int32'); %
NPHOTPHSP = fread (fid, 1, 'int32'); %
EKMAXPHSP = fread (fid, 1, 'float32'); %
EKMINPHSP = fread (fid, 1, 'float32'); %
NINCPPHSP = fread (fid, 1, 'float32'); %
Header_File = struct ('Mode', MODE_RW, 'total_particles', ... NPPHSP,' total_photons', NPHOTPHSP, Max_energy ', ... EKMAXPHSP,' Min_energy ', EKMINPHSP, ...' particles_source ', NINCPPHSP);
MODE_RW = Header_File.Mode;
NPPHSP = Header_File.total_particles;
NPHOTPHSP = Header_File.total_photons;
EKMAXPHSP = Header_File.Max_energy;
EKMINPHSP = Header_File.Min_energy;
NINCPPHSP = Header_File.particles_source;
fid_w = fopen ('prueba.egsphsp1', 'wb');
g = 1;
if g == 0% zlast
a = fwrite (fid_w ,MODE_RW, 'uchar');
b = fwrite (fid_w, NPPHSP, 'int32');
c = fwrite (fid_w, NPHOTPHSP, 'int32');
d = fwrite (fid_w, EKMAXPHSP, 'float32');
e = fwrite (fid_w, EKMINPHSP, 'float32');
f = fwrite (fid_w, NINCPPHSP, 'float32');
'a' and 'MODE_RW' are not of the same class and have different bytes.
I need to read five characters in 5 bytes (1 byte / char). How do I do it?

Accepted Answer

Titus Edelhofer
Titus Edelhofer on 18 Mar 2019
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');
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
  1 Comment
blenis22 on 19 Mar 2019
Dear Titus,
Thank you very much for your contribution (the first option). I had an error in my code, now it works.
Thank you
Greetings, Bladimir

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More Answers (1)

blenis22 on 19 Mar 2019
I need the variable that reads the first five bytes to be of the same class and size in bytes as the variable that is written to the file

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