MATLAB Programming

Accessing Files with Memory-Mapping
• “Example 4 — Modifying Map Parameters” on page 6-58
Improving Performance
MATLAB accesses data in structures more efficiently than it does data
contained in objects. The main reason is that structures do not require the
extra overhead of a subsref routine. Instead of reading directly from the
memmapfile object, as shown here
for k = 1 : N
y(k) = m.Data(k);
end
you will get better performance when you assign the Data field to a variable
and then read or write the mapped file through this variable, as shown in
this second example:
dataRef = m.Data;
for k = 1 : N
y(k) = dataRef(k);
end
Example 1 — Reading a Single Data Type
This example maps a file of 100 double-precision floating-point numbers to
memory. The map begins 1024 bytes from the start of the file, and ends 800
bytes (8 bytes per double times a Repeat value of 100) from that point.
If you haven’t done so already, generate a test data file for use in the following
examples by executing the gendatafile function defined under “Constructing
a memmapfile Object” on page 6-40:
gendatafile('records.dat', 5000);
Now, construct the memmapfile object m, and show the format of its Data
property:
m = memmapfile('records.dat', 'Format', 'double', ...
'Offset', 1024, 'Repeat', 100);
6-55