(octave.info)Binary I/O

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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

     "uint8" (default)
          8-bit unsigned integer.

     "int8"
     "integer*1"
          8-bit signed integer.

     "uint16"
     "ushort"
     "unsigned short"
          16-bit unsigned integer.

     "int16"
     "integer*2"
     "short"
          16-bit signed integer.

     "uint"
     "uint32"
     "unsigned int"
     "ulong"
     "unsigned long"
          32-bit unsigned integer.

     "int"
     "int32"
     "integer*4"
     "long"
          32-bit signed integer.

     "uint64"
          64-bit unsigned integer.

     "int64"
     "integer*8"
          64-bit signed integer.

     "single"
     "float"
     "float32"
     "real*4"
          32-bit floating point number.

     "double"
     "float64"
     "real*8"
          64-bit floating point number.

     "char"
     "char*1"
          8-bit single character.

     "uchar"
     "unsigned char"
          8-bit unsigned character.

     "schar"
     "signed char"
          8-bit signed character.

     The default precision is "uint8".

     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.

     See also: Note: fwrite, Note: fgets, Note:
     fgetl, Note: fscanf, Note: fopen.

 -- : 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.

     See also: Note: fread, Note: fputs, Note:
     fprintf, Note: fopen.