Reading binary file into matlab - matlab

Question

I have a data file that uses (char(1 byte), char[n](array of n chars), word(2 byte unsigned int), short(2 byte signed int), dword(4 byte unsigned int), long(4 byte signed int) and float(4 byte real)) and is supposedly in the following format. I am reading the data file into MATLAB with fopen, fread, etc. but the values I am getting are not what I expect.
Format:
char[8]
<-- outputs 8 ascii values that spell the correct string identifier
dword
<--version of the data files, msw-major version, lsw-minor version (have tried reading as 1 uint32 and 2 uint16's)
dword
dword
dword
dword
<--number of window displays in program
displayinfo[8]
<--contains display window params in the following structure: (not sure what data type this is)
dword
dword
dword
dword
dword
dword
dword
dword
dword
dword
dword
dword
dword
(end of display window params; some are specified as must be a number in [0,3] and they aren't coming out like that)
char[16]
word <-- supposed to be year data was collected (2013) but coming up as 0
Code:
fid = fopen('MIC1.001','rb');
fileIdentifier = fread(fid, 8,'char');
dataFileMajorVersion = fread(fid,1,'uint16');
dateFileMinorVersion = fread(fid,1,'uint16');
numModules = fread(fid,1,'uint32');
fread(fid,1,'uint32'); % value not used
numSwipesCollected = fread(fid,1,'uint32');
numWindowDisplays = fread(fid,1,'uint32');
% display info vars:
displayType = [];
moduleNumber = [];
channelNumber = [];
beginningBar = [];
endBar = [];
vertExpFactor = [];
voltageOffset =[];
isGridEnabled = [];
isEngineeringUnitEnabled = [];
colorOfDisplay = [];
multiChannelIndex = [];
numChannelsForMultiChannelDisp = [];
multiChannelDispStyle = [];
% or does it go through loop for all 8 whether or not there are 8 displays??
for i=1:numWindowDisplays
displayType = [fread(fid,1,'uint32'); displayType];
moduleNumber = [fread(fid,1,'uint32'); moduleNumber];
channelNumber = [fread(fid,1,'uint32'); channelNumber];
beginningBar = [fread(fid,1,'uint32'); beginningBar];
endBar = [fread(fid,1,'uint32'); endBar];
vertExpFactor = [fread(fid,1,'uint32'); vertExpFactor];
voltageOffset =[fread(fid,1,'uint32'); voltageOffset];
isGridEnabled = [fread(fid,1,'uint32'); isGridEnabled];
isEngineeringUnitEnabled = [fread(fid,1,'uint32'); isEngineeringUnitEnabled];
colorOfDisplay = [fread(fid,1,'uint32'); colorOfDisplay];
multiChannelIndex = [fread(fid,1,'uint32'); multiChannelIndex];
numChannelsForMultiChannelDisp = [fread(fid,1,'uint32'); numChannelsForMultiChannelDisp];
multiChannelDispStyle = [fread(fid,1,'uint32'); multiChannelDispStyle];
end
fread(fid,1,'uint32'); % value only used internally
fread(fid,16,'char'); % unused parameter for future use
yearOfDataCollection = fread(fid,1,'uint16');

Answer 1

I would recommend first, just read in all the data at once as a byte array. You'll be able to debug the problem much faster:
fid = fopen('MIC1.001','rb');
data = fread(fid);
fclose(fid);
% could look at it as all chars, just for debugging
char(A)'
The data is read in as a large array of bytes. Then you would go through and parse the bytes by casting them appropriately. You may want to try just testing your method first:
% create a binary file to follow the same format as the specified file
fid = fopen('test.dat','wb');
% Put in 8 character string for file ID
aa = 'myfile0';
fwrite(fid,aa);
% Null terminate it, (I guess)
fwrite(fid,0);
% write the 2 byte file major revision
aa = 1000;
fwrite(fid,aa,'uint16');
% write the 2 byte file minor revision
aa = 5000;
fwrite(fid,aa,'uint16');
% write the 4 byte number of modules
aa = 65536;
fwrite(fid,aa,'uint32');
fclose(fid);
% read the entire file in
fid = fopen('test.dat','rb');
A = fread(fid);
fclose(fid);
% Try to read the file id
disp(char(A(1:8))')
% Try to read the file major revision
majorByte1 = dec2hex(A(9));
majorByte2 = dec2hex(A(10));
% see if it needs byte swapped
tmp1 = hex2dec([majorByte1 majorByte2]);
tmp2 = hex2dec([majorByte2 majorByte1]);
fprintf(1,'File Major: %d ? = %d\nFile Major: %d ? = %d\n',1000,tmp1,1000,tmp2);
For output I get:
myfile0
File Major: 1000 ? = 3715
File Major: 1000 ? = 1000
So, for me, I'll need to byte swap the data, maybe you do too? :-)
EDIT
To do this using fread, from the Matlab docs:
A = fread(fileID, sizeA, precision, skip, machineformat) reads data
with the specified machineformat.
For your case:
A = fread(fid,2,'uint16',0,'b');
I'm assuming you're on a little endian machine, to swap it to little endian, just use a l instead of a b.

Answer 2

number of digit of dec2hex conversion should be given (0x0A0C != 0xAC):
majorByte1 = dec2hex(A(9), 2);
majorByte2 = dec2hex(A(10), 2);
% see if it needs byte swapped
tmp1 = hex2dec([majorByte1 majorByte2]);
tmp2 = hex2dec([majorByte2 majorByte1]);