How to specify the output type of an fread(fid...) ?

fread(...) lets you specify the data type of the data to be read, but appears to always return the results in a matrix of doubles.

d = fread(fid, nc, 'int16');

K>> whos d

Name Size Bytes Class Attributes

d 46080x1 368640 double

That's not a problem for small data amounts, but I need to read files with 2-4 GB files with int16 data and work with it. Reading the a 4 GB file of int16's (2 billion elements) results in a 16 GB array of doubles, which I then need to convert back to int16's, so effectively temporarily uses 18 GB of memory.

Q: is there any way to specify the output data type, or tell fread to return the data in the same data type that it read from the file?

My current work-around is to preallocate an array of int16's, and read the the file in smaller chunks, converting each chunk from doubles back to int16's.

Anybody got a better solution?

Answer 1

[per isakson]

Try this little experiment (based on the first example in the doc)

%%
fid = fopen('nine.bin','w');
fwrite(fid,[1:9]);
fclose(fid);
%%
fid = fopen('nine.bin','r');
num = fread( fid, [1,9], 'uint8=>uint8' );
fclose(fid);

and

>> whos num
  Name      Size            Bytes  Class    Attributes
  num       1x9                 9  uint8 

[Ian]

Excellent. Thanks. I missed that in the documentation, but indeed it's there if one squints hard enough...