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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');
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2 Answers 2

Reset to default
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.

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5 Comments

But when you don't specify the data type, doesn't MATLAB read it wrong? And if I specified them all as chars, which they are not, it would definitely read them wrong I thought..
@MarissaSileo, updated the answer, if you read them all as chars, or bytes, and assemble them later, it's ok.
Okay when I put it in MATLAB I get the same output as you. Forgive me for not knowing much about this, but I'm still a little lost. I've been trying to read up on the byte swapping as you mentioned but I was under the impression that MATLAB would pick up on whether the data was big or little endian and would then convert it accordingly. Am I wrong in assuming that? Maybe that is why I am getting random values like 2778916 when my data system manual says it should be a number between 0 and 3...
@MarissaSileo, np! Matlab doesn't have a way that I am aware of, to automagically figure out the endian of the file. Sounds like you've got your culprit here, sounds like you need to swap bytes.
Don't byte swap like that. Instead do A(9:10) * [256; 1]. Numeric manipulation is much faster than string work, and avoid the string problems Maurice points out with padding / leading zeros.
0

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]);
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1 Comment

Just A(9:10) * [256; 1] seems so much better than converting to strings in between. The other byte order is easy to get as well: A(9:10) * [1; 256]

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