octave: Binary I/O
14.2.16 Binary I/O
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Octave can read and write binary data using the functions ‘fread’ and
‘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.
-- : VAL = fread (FID)
-- : VAL = fread (FID, SIZE)
-- : VAL = fread (FID, SIZE, PRECISION)
-- : VAL = fread (FID, SIZE, PRECISION, SKIP)
-- : VAL = fread (FID, SIZE, PRECISION, SKIP, ARCH)
-- : [VAL, COUNT] = fread (...)
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
‘Inf’
Read as much as possible, returning a column vector.
‘NR’
Read up to NR elements, returning a column vector.
‘[NR, Inf]’
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.
‘[NR, NC]’
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
"schar"
"signed char"
Signed character.
"uchar"
"unsigned char"
Unsigned character.
"int8"
"integer*1"
8-bit signed integer.
"int16"
"integer*2"
16-bit signed integer.
"int32"
"integer*4"
32-bit signed integer.
"int64"
"integer*8"
64-bit signed integer.
"uint8"
8-bit unsigned integer.
"uint16"
16-bit unsigned integer.
"uint32"
32-bit unsigned integer.
"uint64"
64-bit unsigned integer.
"single"
"float32"
"real*4"
32-bit floating point number.
"double"
"float64"
"real*8"
64-bit floating point number.
"char"
"char*1"
Single character.
"short"
Short integer (size is platform dependent).
"int"
Integer (size is platform dependent).
"long"
Long integer (size is platform dependent).
"ushort"
"unsigned short"
Unsigned short integer (size is platform dependent).
"uint"
"unsigned int"
Unsigned integer (size is platform dependent).
"ulong"
"unsigned long"
Unsigned long integer (size is platform dependent).
"float"
Single precision floating point number (size is platform
dependent).
The default precision is "uchar".
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 default,
‘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
precision values.
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
"native" or "n"
The format of the current machine.
"ieee-be" or "b"
IEEE big endian.
"ieee-le" or "l"
IEEE little endian.
If no ARCH is given the value used in the call to ‘fopen’ which
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.
DONTPRINTYET See also: 
fwrite XREFfwrite, fgets XREFfgets, *noteDONTPRINTYET See also: fwrite XREFfwrite, fgets XREFfgets,
fgetl XREFfgetl, fscanf XREFfscanf, fopen XREFfopen.
-- : fwrite (FID, DATA)
-- : fwrite (FID, DATA, PRECISION)
-- : fwrite (FID, DATA, PRECISION, SKIP)
-- : fwrite (FID, DATA, PRECISION, SKIP, ARCH)
-- : COUNT = fwrite (...)
Write data in binary form to the file specified by the file
descriptor FID, returning the number of values COUNT successfully
written to the file.
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 ‘fread’.
The behavior of ‘fwrite’ is undefined if the values in DATA are too
large to fit in the specified precision.
DONTPRINTYET See also: fread XREFfread, fputs XREFfputs, *noteDONTPRINTYET See also: fread XREFfread, fputs XREFfputs,
fprintf XREFfprintf, fopen XREFfopen.
Info Catalog
octave: String Input Conversions
octave: C-Style I/O Functions
octave: Temporary Files