MATLAB Programming

Accessing Files with Memory-Mapping
ans =
500 500 500 500 500 500 500 500
500 500 500 500 500 500 500 500
500 500 500 500 500 500 500 500
Selecting Appropriate Data Types
All of the usual MATLAB indexing and data type rules apply when assigning
values to data via a memory map. The data type that you assign to must be
big enough to hold the value being assigned. For example,
m = memmapfile('records.dat', 'Format', 'uint8', ...
'Writable', true);
d = m.Data;
d(5) = 300;
saturates the x variable because x is defined as an 8-bit integer:
d(5)
ans =
255
Working with Copies of the Mapped Data
In the following code, the data in variable block2 is a copy ofthefiledata
mapped by m.Data(2). Because it is a copy, modifying array data in block2
does not modify the data contained in the file:
First, destroy the memmapfile object and restore the test file records.dat,
since it has been modified by running the previous examples:
clear m
gendatafile('records.dat',50000);
Map the file as a series of uint16 and double matrices and make a copy of
m.Data(2) in block2:
m = memmapfile('records.dat', ...
'Format', { ...
'uint16' [5 8] 'x'; ...
'double' [4 5] 'y' });
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