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<a name="Binary-I_002fO"></a>
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Next: <a href="Temporary-Files.html#Temporary-Files" accesskey="n" rel="next">Temporary Files</a>, Previous: <a href="String-Input-Conversions.html#String-Input-Conversions" accesskey="p" rel="prev">String Input Conversions</a>, Up: <a href="C_002dStyle-I_002fO-Functions.html#C_002dStyle-I_002fO-Functions" accesskey="u" rel="up">C-Style I/O Functions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Binary-I_002fO-1"></a>
<h4 class="subsection">14.2.16 Binary I/O</h4>
<p>Octave can read and write binary data using the functions <code>fread</code>
and <code>fwrite</code>, 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.
</p>
<a name="XREFfread"></a><dl>
<dt><a name="index-fread"></a><em><var>val</var> =</em> <strong>fread</strong> <em>(<var>fid</var>)</em></dt>
<dt><a name="index-fread-1"></a><em><var>val</var> =</em> <strong>fread</strong> <em>(<var>fid</var>, <var>size</var>)</em></dt>
<dt><a name="index-fread-2"></a><em><var>val</var> =</em> <strong>fread</strong> <em>(<var>fid</var>, <var>size</var>, <var>precision</var>)</em></dt>
<dt><a name="index-fread-3"></a><em><var>val</var> =</em> <strong>fread</strong> <em>(<var>fid</var>, <var>size</var>, <var>precision</var>, <var>skip</var>)</em></dt>
<dt><a name="index-fread-4"></a><em><var>val</var> =</em> <strong>fread</strong> <em>(<var>fid</var>, <var>size</var>, <var>precision</var>, <var>skip</var>, <var>arch</var>)</em></dt>
<dt><a name="index-fread-5"></a><em>[<var>val</var>, <var>count</var>] =</em> <strong>fread</strong> <em>(…)</em></dt>
<dd><p>Read binary data from the file specified by the file descriptor <var>fid</var>.
</p>
<p>The optional argument <var>size</var> specifies the amount of data to read
and may be one of
</p>
<dl compact="compact">
<dt><code>Inf</code></dt>
<dd><p>Read as much as possible, returning a column vector.
</p>
</dd>
<dt><code><var>nr</var></code></dt>
<dd><p>Read up to <var>nr</var> elements, returning a column vector.
</p>
</dd>
<dt><code>[<var>nr</var>, Inf]</code></dt>
<dd><p>Read as much as possible, returning a matrix with <var>nr</var> rows. If the
number of elements read is not an exact multiple of <var>nr</var>, the last
column is padded with zeros.
</p>
</dd>
<dt><code>[<var>nr</var>, <var>nc</var>]</code></dt>
<dd><p>Read up to <code><var>nr</var> * <var>nc</var></code> elements, returning a matrix with
<var>nr</var> rows. If the number of elements read is not an exact multiple
of <var>nr</var>, the last column is padded with zeros.
</p></dd>
</dl>
<p>If <var>size</var> is omitted, a value of <code>Inf</code> is assumed.
</p>
<p>The optional argument <var>precision</var> is a string specifying the type of
data to read and may be one of
</p>
<dl compact="compact">
<dt><code>"uint8"</code> (default)</dt>
<dd><p>8-bit unsigned integer.
</p>
</dd>
<dt><code>"int8"</code></dt>
<dt><code>"integer*1"</code></dt>
<dd><p>8-bit signed integer.
</p>
</dd>
<dt><code>"uint16"</code></dt>
<dt><code>"ushort"</code></dt>
<dt><code>"unsigned short"</code></dt>
<dd><p>16-bit unsigned integer.
</p>
</dd>
<dt><code>"int16"</code></dt>
<dt><code>"integer*2"</code></dt>
<dt><code>"short"</code></dt>
<dd><p>16-bit signed integer.
</p>
</dd>
<dt><code>"uint"</code></dt>
<dt><code>"uint32"</code></dt>
<dt><code>"unsigned int"</code></dt>
<dt><code>"ulong"</code></dt>
<dt><code>"unsigned long"</code></dt>
<dd><p>32-bit unsigned integer.
</p>
</dd>
<dt><code>"int"</code></dt>
<dt><code>"int32"</code></dt>
<dt><code>"integer*4"</code></dt>
<dt><code>"long"</code></dt>
<dd><p>32-bit signed integer.
</p>
</dd>
<dt><code>"uint64"</code></dt>
<dd><p>64-bit unsigned integer.
</p>
</dd>
<dt><code>"int64"</code></dt>
<dt><code>"integer*8"</code></dt>
<dd><p>64-bit signed integer.
</p>
</dd>
<dt><code>"single"</code></dt>
<dt><code>"float"</code></dt>
<dt><code>"float32"</code></dt>
<dt><code>"real*4"</code></dt>
<dd><p>32-bit floating point number.
</p>
</dd>
<dt><code>"double"</code></dt>
<dt><code>"float64"</code></dt>
<dt><code>"real*8"</code></dt>
<dd><p>64-bit floating point number.
</p>
</dd>
<dt><code>"char"</code></dt>
<dt><code>"char*1"</code></dt>
<dd><p>8-bit single character.
</p>
</dd>
<dt><code>"uchar"</code></dt>
<dt><code>"unsigned char"</code></dt>
<dd><p>8-bit unsigned character.
</p>
</dd>
<dt><code>"schar"</code></dt>
<dt><code>"signed char"</code></dt>
<dd><p>8-bit signed character.
</p>
</dd>
</dl>
<p>The default precision is <code>"uint8"</code>.
</p>
<p>The <var>precision</var> argument may also specify an optional repeat
count. For example, ‘<samp>32*single</samp>’ causes <code>fread</code> to read
a block of 32 single precision floating point numbers. Reading in
blocks is useful in combination with the <var>skip</var> argument.
</p>
<p>The <var>precision</var> argument may also specify a type conversion.
For example, ‘<samp>int16=>int32</samp>’ causes <code>fread</code> to read 16-bit
integer values and return an array of 32-bit integer values. By
default, <code>fread</code> returns a double precision array. The special
form ‘<samp>*TYPE</samp>’ is shorthand for ‘<samp>TYPE=>TYPE</samp>’.
</p>
<p>The conversion and repeat counts may be combined. For example, the
specification ‘<samp>32*single=>single</samp>’ causes <code>fread</code> 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.
</p>
<p>The optional argument <var>skip</var> 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,
</p>
<div class="example">
<pre class="example">fread (f, 10, "3*single=>single", 8)
</pre></div>
<p>will omit the final 8-byte skip because the last read will not be
a complete block of 3 values.
</p>
<p>The optional argument <var>arch</var> is a string specifying the data format
for the file. Valid values are
</p>
<dl compact="compact">
<dt><code>"native"</code> or <code>"n"</code></dt>
<dd><p>The format of the current machine.
</p>
</dd>
<dt><code>"ieee-be"</code> or <code>"b"</code></dt>
<dd><p>IEEE big endian.
</p>
</dd>
<dt><code>"ieee-le"</code> or <code>"l"</code></dt>
<dd><p>IEEE little endian.
</p></dd>
</dl>
<p>If no <var>arch</var> is given the value used in the call to <code>fopen</code> which
created the file descriptor is used. Otherwise, the value specified with
<code>fread</code> overrides that of <code>fopen</code> and determines the data format.
</p>
<p>The output argument <var>val</var> contains the data read from the file.
</p>
<p>The optional return value <var>count</var> contains the number of elements read.
</p>
<p><strong>See also:</strong> <a href="#XREFfwrite">fwrite</a>, <a href="Line_002dOriented-Input.html#XREFfgets">fgets</a>, <a href="Line_002dOriented-Input.html#XREFfgetl">fgetl</a>, <a href="Formatted-Input.html#XREFfscanf">fscanf</a>, <a href="Opening-and-Closing-Files.html#XREFfopen">fopen</a>.
</p></dd></dl>
<a name="XREFfwrite"></a><dl>
<dt><a name="index-fwrite"></a><em></em> <strong>fwrite</strong> <em>(<var>fid</var>, <var>data</var>)</em></dt>
<dt><a name="index-fwrite-1"></a><em></em> <strong>fwrite</strong> <em>(<var>fid</var>, <var>data</var>, <var>precision</var>)</em></dt>
<dt><a name="index-fwrite-2"></a><em></em> <strong>fwrite</strong> <em>(<var>fid</var>, <var>data</var>, <var>precision</var>, <var>skip</var>)</em></dt>
<dt><a name="index-fwrite-3"></a><em></em> <strong>fwrite</strong> <em>(<var>fid</var>, <var>data</var>, <var>precision</var>, <var>skip</var>, <var>arch</var>)</em></dt>
<dt><a name="index-fwrite-4"></a><em><var>count</var> =</em> <strong>fwrite</strong> <em>(…)</em></dt>
<dd><p>Write data in binary form to the file specified by the file descriptor
<var>fid</var>, returning the number of values <var>count</var> successfully written
to the file.
</p>
<p>The argument <var>data</var> is a matrix of values that are to be written to
the file. The values are extracted in column-major order.
</p>
<p>The remaining arguments <var>precision</var>, <var>skip</var>, and <var>arch</var> are
optional, and are interpreted as described for <code>fread</code>.
</p>
<p>The behavior of <code>fwrite</code> is undefined if the values in <var>data</var>
are too large to fit in the specified precision.
</p>
<p><strong>See also:</strong> <a href="#XREFfread">fread</a>, <a href="Simple-Output.html#XREFfputs">fputs</a>, <a href="Formatted-Output.html#XREFfprintf">fprintf</a>, <a href="Opening-and-Closing-Files.html#XREFfopen">fopen</a>.
</p></dd></dl>
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