Creating a memory mapped file

7 views (last 30 days)
Ken on 31 Aug 2016
Commented: Ken on 1 Sep 2016
I am trying to create a new memory-mapped 'big data' file by using sequential writes of structured binary data, where I write a vector of values for each variable separately. First, can I start with an empty file that I have opened for write? I cannot seem to write an array into mapped location unless data already exists at that location. See below
%%define the memory map for the output binary file
OutFile = 'testOutFile';
fid = fopen('test.lls','w');
mmLLS = memmapfile('test.lls',...
'Format',{ ...
'single' 1 'lat'; ...
'single' 1 'lon'},...
Lat = single(32.3);
Lon = single(-110.2); = Lat;
Error using memmapfile/subsasgn (line 732)
A subscripting operation on the Data field attempted to create a
comma-separated list. The memmapfile class does not support the use
of comma-separated lists when subscripting.
  1 Comment
per isakson
per isakson on 31 Aug 2016
Edited: per isakson on 31 Aug 2016
"First, can I start with an empty file that I have opened for write?" &nbsp The short answer is NO!
Doc says: "Memory-mapping is a mechanism that maps a portion of a [existing] file, or an entire [existing] file, on disk to a range of addresses within an application's address space."

Sign in to comment.

Accepted Answer

Walter Roberson
Walter Roberson on 1 Sep 2016
"memmapfile does not expand or append to a mapped file. Use instead standard file I/O functions like fopen and fwrite."
  1 Comment
Ken on 1 Sep 2016
Thank you for this clarification, although it is disappointing, when combined with the fact that Matlab cannot write sequences of binary complex structures.
It would be helpful if this fact were stated clearly/explicitly when describing the capability to write to a memory mapped file.

Sign in to comment.

More Answers (0)



Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!