MATLAB Programming

Accessing Files with Memory-Mapping
• If you specify a repeat value other than Inf, and that value would cause the
map to extend beyond the end of the file, then MATLAB generates an error.
Considering the last example, if the part of the file from m.Offset to the end
were 70 bytes (instead of the 72 bytes required to repeat m.Format three
times) and you used a Repeat value of Inf, then only two full repetitions of
the specified format would have been mapped. The end result would be as if
you had constructed the map with this command:
m = memmapfile('records.dat', ...
'Offset', 2048, ...
'Format', { ...
'int16' [2 2] 'model'; ...
'uint32' [1 1] 'serialno'; ...
'single' [1 3] 'expenses'}, ...
'Repeat', 2);
If Repeat were set to 3 and you had only 70 bytes to the end of the file, you
would get an error.
Note memmapfile does not expand or append to a mapped file. Use standard
file I/O functions like fopen and fwrite to do this.
Setting the Type of Access
You can map a file region to allow either read-only or read and write access
to its contents. Pass a Writable parameter and value in the memmapfile
constructor, or set m.Writable on an existing object to set the type of access
allowed:
objname = memmapfile(filename, 'Writable', trueorfalse)
The value passed can be either true (equal to logical(1)) orfalse (equal
to logical(0)). By default, it is false, meaning that the mapped region
is read only.
To map a read and write region of the file records.dat in memory, type
m = memmapfile('records.dat', 'Writable', true);
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