How to invert the function typecast?

Hello,

I am using typecast to convert from double to uint8 and store some data in a file:

 fwrite(fid,typecast(double(data),'uint8'),'uint8');

Now, I want to read this data back, but if I use fread like this:

 data2 = fread(fid, length(data), 'double');

when it finds a value equivalent to a new line (10) or carriage return (13) - I am not sure which one of those actually is - it corrupts the data read after that value.

How can I avoid this problem? I need to write the data using uint8 because I need to read it from an ARM, process it, write it back, and read it in Matlab.

I do not know if there is a better way of doing all this.

Thanks!

[Dani Tormo]

I have just checked. The error comes when it finds a new line character (10). Even in the ARM, when the reading function finds a 10, all the data read after it becomes corrupted.

So, how can I prevent this to happen?

[James Tursa]

Please show all of your relevant code, including your fopen statements, what is the class and size of the variable data, all of your fwrite and fread statements, etc.

[Dani Tormo]

Writing the data into the SD card (data_array is a 10000x1 array in double-precision format):

 fid = fopen('asdf.txt','wt');
 fwrite(fid,typecast(data_array,'uint8'),'uint8');
 fclose(fid);

Reading back the data from the SD card:

 fid = fopen('asdf.txt','r');
 data_array2 = fread(fid, length(data_array), 'double');
 fclose(fid);

If I open the file asdf.txt with notepad, I can see when comes the first new line (at the position 190). I checked what value is occupying that position (taking into account the 8 bits of the double), and there is the 10 (ASCII equivalent to new line), in the sixth position of the 24th double-precision value. Exactly the first value which becomes corrupted when reading the data.

Answer 1

[James Tursa]

Don't open the file as a text file with 'wt'. Instead, open it as binary by leaving off the 't' part. E.g.,

 fid = fopen('asdf.txt','w');

(And, since it is a binary file you would probably use a different file extension other than .txt)

[Dani Tormo]

Like a charm.

Thanks!