MATLAB Programming

Accessing Files with Memory-Mapping
d(2).x
ans =
52995 7353 47792 25316 35687 65535 65535 25262
65535 65535 25290 65285 13436 7773 25296 65535
27623 25307 65535 65535 65535 25313 39561 42855
25175 6534 65535 65535 25287 57641 24101 49977
65535 65535 65535 25292 28323 59736 65535 25304
This section covers the following topics:
• “Dimensions of the Data Field” on page 6-61
• “Writing Matrices to a Mapped File” on page 6-62
• “Selecting Appropriate Data Types” on page 6-65
• “Working with Copies of the Mapped Data” on page 6-65
• “Invalid Syntax for Writing to Mapped Memory” on page 6-66
Dimensions of the Data Field
The dimensions of a memmapfile object’s Data fieldaresetatthetimeyou
construct the object and cannot be changed. This differs from other MATLAB
arrays that have dimensions you can modify using subscripted assignment.
For example, you can add a new column to the field of a MATLAB structure:
A.s = ones(4,5);
A.s(:,6) = [1 2 3 4];
size(A.s)
ans =
4 6
% Add new column to A.s
But not to a similar field of a structure that represents data mapped from a
file. The following assignment to m.Data(60).y does not expand the size
of y, but instead generates an error:
m.Data(60)
ans =
x: [5x8 uint16]
y: [4x5 double]
6-61