Octave can read and write binary data using the functions
fwrite, which are patterned after the standard C functions
with the same names. They are able to automatically swap the byte order
of integer data and convert among the supported floating point formats
as the data are read.
Read binary data from the file specified by the file descriptor fid.
The optional argument size specifies the amount of data to read and may be one of
Read as much as possible, returning a column vector.
Read up to nr elements, returning a column vector.
Read as much as possible, returning a matrix with nr rows. If the number of elements read is not an exact multiple of nr, the last column is padded with zeros.
Read up to
nr * nc elements, returning a matrix with
nr rows. If the number of elements read is not an exact multiple
of nr, the last column is padded with zeros.
If size is omitted, a value of
Inf is assumed.
The optional argument precision is a string specifying the type of data to read and may be one of
8-bit unsigned integer.
8-bit signed integer.
16-bit unsigned integer.
16-bit signed integer.
32-bit unsigned integer.
32-bit signed integer.
64-bit unsigned integer.
64-bit signed integer.
32-bit floating point number.
64-bit floating point number.
8-bit single character.
8-bit unsigned character.
8-bit signed character.
The default precision is
The precision argument may also specify an optional repeat
count. For example, ‘32*single’ causes
fread to read
a block of 32 single precision floating point numbers. Reading in
blocks is useful in combination with the skip argument.
The precision argument may also specify a type conversion.
For example, ‘int16=>int32’ causes
fread to read 16-bit
integer values and return an array of 32-bit integer values. By
fread returns a double precision array. The special
form ‘*TYPE’ is shorthand for ‘TYPE=>TYPE’.
The conversion and repeat counts may be combined. For example, the
specification ‘32*single=>single’ causes
fread to read
blocks of single precision floating point values and return an array
of single precision values instead of the default array of double
The optional argument skip specifies the number of bytes to skip after each element (or block of elements) is read. If it is not specified, a value of 0 is assumed. If the final block read is not complete, the final skip is omitted. For example,
fread (f, 10, "3*single=>single", 8)
will omit the final 8-byte skip because the last read will not be a complete block of 3 values.
The optional argument arch is a string specifying the data format for the file. Valid values are
The format of the current machine.
IEEE big endian.
IEEE little endian.
If no arch is given the value used in the call to
created the file descriptor is used. Otherwise, the value specified with
fread overrides that of
fopen and determines the data format.
The output argument val contains the data read from the file.
The optional return value count contains the number of elements read.
Write data in binary form to the file specified by the file descriptor fid.
The argument data is a matrix of values that are to be written to the file. The values are extracted in column-major order.
The remaining arguments precision, skip, and arch are
optional, and are interpreted as described for
The output count is the number of data items successfully written.
Programming Note: The behavior of
fwrite is undefined if the values in
data are too large to fit in the specified precision.