MATLAB Programming

Accessing Files with Memory-Mapping
• “Mapping of the Example File” on page 6-50
• “Repeating a Format Scheme” on page 6-52
• “Setting the Type of Access” on page 6-53
All the examples in this section use a file named records.dat that contains
a 5000-by-1 matrix of double-precision floating point numbers. Use the
following code to generate this file before going on to the next sections of this
documentation.
First, save this function in your current working directory:
function gendatafile(filename, count)
dmax32 = double(intmax('uint32'));
rand('state', 0)
fid = fopen(filename,'w');
fwrite(fid, rand(count,1)*dmax32, 'double');
fclose(fid);
Now execute the gendatafile function to generate the records.dat file
that is referenced in this section. You can use this function at any time to
regenerate the file:
gendatafile('records.dat', 5000);
Constructing the Object with Default Property Values
The simplest and most general way to call the constructor is with one input
argument that specifies the name of the file you want to map. All other
properties are optional and are given their default values. Use the syntax
shown here:
objname = memmapfile(filename)
To construct a map for the file records.dat that resides in your current
working directory, type the following:
m = memmapfile('records.dat')
m =
Filename: 'd:\matlab\mfiles\records.dat'
6-41