MATLAB Programming

6 Data Import and Export
For example, say that you map a file that is 12K bytes in length. Data read
from this file could be treated as a sequence of 6,000 16-bit (2-byte) integers,
or as 1,500 8-byte double-precision floating-point numbers, to name just a
couple of possibilities. Or you could read this data in as a combination of
different types: for example, as 4,000 8-bit (1-byte) integers followed by 1,000
64-bit (8-byte) integers. You determine how MATLAB will interpret the
mapped data by setting the Format property of the memmapfile object when
you call its constructor.
Note MATLAB arrays are stored on disk in column-major order. (The
sequence of array elements is column 1, row1;column1,row2;column1,last
row; column 2, row 1, and so on.) You might need to transpose or rearrange
the order of array elements when reading or writing via a memory map.
Note The Sol64 platform supports aligned data access only. If you attempt to
use a memmapfile format on Sol64 that does not take the necessary alignment
considerations into account, MATLAB generates an error. (See “Aligned
Access on Sol64” on page 6-37).
Data types supported for the Format property are shown at the end of this
section. See “Supported Data Types for the Format Property” on page 6-51.
For more information on format options see
• “Mapping a Single Data Type” on page 6-46
• “Formatting the Mapped Data to an Array” on page 6-47
• “Mapping Multiple Data Types and Arrays” on page 6-49
Mapping a Single Data Type. If the file region being mapped contains data
of only one type, specify the Format value as a character string identifying
that type:
objname = memmapfile(filename, 'Format', datatype)
6-46