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<h4 class="subsection" id="Formatted-Input-1"><span>14.2.11 Formatted Input<a class="copiable-link" href="#Formatted-Input-1"> ¶</a></span></h4>
<p>Octave provides the <code class="code">scanf</code>, <code class="code">fscanf</code>, and <code class="code">sscanf</code>
functions to read formatted input. There are two forms of each of these
functions. One can be used to extract vectors of data from a file, and
the other is more ‘C-like’.
</p>
<a class="anchor" id="XREFfscanf"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-fscanf"><span><code class="def-type">[<var class="var">val</var>, <var class="var">count</var>, <var class="var">errmsg</var>] =</code> <strong class="def-name">fscanf</strong> <code class="def-code-arguments">(<var class="var">fid</var>, <var class="var">template</var>, <var class="var">size</var>)</code><a class="copiable-link" href="#index-fscanf"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-fscanf-1"><span><code class="def-type">[<var class="var">v1</var>, <var class="var">v2</var>, …, <var class="var">count</var>, <var class="var">errmsg</var>] =</code> <strong class="def-name">fscanf</strong> <code class="def-code-arguments">(<var class="var">fid</var>, <var class="var">template</var>, "C")</code><a class="copiable-link" href="#index-fscanf-1"> ¶</a></span></dt>
<dd><p>In the first form, read from <var class="var">fid</var> according to <var class="var">template</var>,
returning the result in the matrix <var class="var">val</var>.
</p>
<p>The optional argument <var class="var">size</var> specifies the amount of data to read
and may be one of
</p>
<dl class="table">
<dt><code class="code">Inf</code></dt>
<dd><p>Read as much as possible, returning a column vector.
</p>
</dd>
<dt><code class="code"><var class="var">nr</var></code></dt>
<dd><p>Read up to <var class="var">nr</var> elements, returning a column vector.
</p>
</dd>
<dt><code class="code">[<var class="var">nr</var>, Inf]</code></dt>
<dd><p>Read as much as possible, returning a matrix with <var class="var">nr</var> rows. If the
number of elements read is not an exact multiple of <var class="var">nr</var>, the last
column is padded with zeros.
</p>
</dd>
<dt><code class="code">[<var class="var">nr</var>, <var class="var">nc</var>]</code></dt>
<dd><p>Read up to <code class="code"><var class="var">nr</var> * <var class="var">nc</var></code> elements, returning a matrix with
<var class="var">nr</var> rows. If the number of elements read is not an exact multiple
of <var class="var">nr</var>, the last column is padded with zeros.
</p></dd>
</dl>
<p>If <var class="var">size</var> is omitted, a value of <code class="code">Inf</code> is assumed.
</p>
<p>A string is returned if <var class="var">template</var> specifies only character conversions.
</p>
<p>The number of items successfully read is returned in <var class="var">count</var>.
</p>
<p>If an error occurs, <var class="var">errmsg</var> contains a system-dependent error message.
</p>
<p>In the second form, read from <var class="var">fid</var> according to <var class="var">template</var>,
with each conversion specifier in <var class="var">template</var> corresponding to a
single scalar return value. This form is more “C-like”, and also
compatible with previous versions of Octave. The number of successful
conversions is returned in <var class="var">count</var>
</p>
<p>See the Formatted Input section of the GNU Octave manual for a
complete description of the syntax of the template string.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="Line_002dOriented-Input.html#XREFfgets">fgets</a>, <a class="ref" href="Line_002dOriented-Input.html#XREFfgetl">fgetl</a>, <a class="ref" href="Binary-I_002fO.html#XREFfread">fread</a>, <a class="ref" href="#XREFscanf">scanf</a>, <a class="ref" href="#XREFsscanf">sscanf</a>, <a class="ref" href="Opening-and-Closing-Files.html#XREFfopen">fopen</a>.
</p></dd></dl>
<a class="anchor" id="XREFscanf"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-scanf"><span><code class="def-type">[<var class="var">val</var>, <var class="var">count</var>, <var class="var">errmsg</var>] =</code> <strong class="def-name">scanf</strong> <code class="def-code-arguments">(<var class="var">template</var>, <var class="var">size</var>)</code><a class="copiable-link" href="#index-scanf"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-scanf-1"><span><code class="def-type">[<var class="var">v1</var>, <var class="var">v2</var>, …, <var class="var">count</var>, <var class="var">errmsg</var>] =</code> <strong class="def-name">scanf</strong> <code class="def-code-arguments">(<var class="var">template</var>, "C")</code><a class="copiable-link" href="#index-scanf-1"> ¶</a></span></dt>
<dd><p>This is equivalent to calling <code class="code">fscanf</code> with <var class="var">fid</var> = <code class="code">stdin</code>.
</p>
<p>It is currently not useful to call <code class="code">scanf</code> in interactive programs.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="#XREFfscanf">fscanf</a>, <a class="ref" href="#XREFsscanf">sscanf</a>, <a class="ref" href="Formatted-Output.html#XREFprintf">printf</a>.
</p></dd></dl>
<a class="anchor" id="XREFsscanf"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-sscanf"><span><code class="def-type">[<var class="var">val</var>, <var class="var">count</var>, <var class="var">errmsg</var>, <var class="var">pos</var>] =</code> <strong class="def-name">sscanf</strong> <code class="def-code-arguments">(<var class="var">string</var>, <var class="var">template</var>, <var class="var">size</var>)</code><a class="copiable-link" href="#index-sscanf"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-sscanf-1"><span><code class="def-type">[<var class="var">v1</var>, <var class="var">v2</var>, …, <var class="var">count</var>, <var class="var">errmsg</var>] =</code> <strong class="def-name">sscanf</strong> <code class="def-code-arguments">(<var class="var">string</var>, <var class="var">template</var>, "C")</code><a class="copiable-link" href="#index-sscanf-1"> ¶</a></span></dt>
<dd><p>This is like <code class="code">fscanf</code>, except that the characters are taken from the
string <var class="var">string</var> instead of from a stream.
</p>
<p>Reaching the end of the string is treated as an end-of-file condition. In
addition to the values returned by <code class="code">fscanf</code>, the index of the next
character to be read is returned in <var class="var">pos</var>.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="#XREFfscanf">fscanf</a>, <a class="ref" href="#XREFscanf">scanf</a>, <a class="ref" href="Formatted-Output.html#XREFsprintf">sprintf</a>.
</p></dd></dl>
<p>Calls to <code class="code">scanf</code> are superficially similar to calls to
<code class="code">printf</code> in that arbitrary arguments are read under the control of
a template string. While the syntax of the conversion specifications in
the template is very similar to that for <code class="code">printf</code>, the
interpretation of the template is oriented more towards free-format
input and simple pattern matching, rather than fixed-field formatting.
For example, most <code class="code">scanf</code> conversions skip over any amount of
“white space” (including spaces, tabs, and newlines) in the input
file, and there is no concept of precision for the numeric input
conversions as there is for the corresponding output conversions.
Ordinarily, non-whitespace characters in the template are expected to
match characters in the input stream exactly. For example, note that
<code class="code">sscanf</code> parses the string and whitespace differently when using
mixed numeric and string output types:
<a class="index-entry-id" id="index-conversion-specifications-_0028scanf_0029"></a>
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">teststr = "1 is a lonely number";
sscanf (teststr, "%s is a %s")
⇒ 1lonelynumber
sscanf (teststr, "%g is a %s")
⇒
1
108
111
110
101
108
121
[a, b, c] = sscanf ("1 is a lonely number", "%g is a %s %s", "C")
⇒ a = 1
⇒ b = lonely
⇒ c = number
</pre></div></div>
<p>When a <em class="dfn">matching failure</em> occurs, <code class="code">scanf</code> returns immediately,
leaving the first non-matching character as the next character to be
read from the stream, and <code class="code">scanf</code> returns all the items that were
successfully converted.
<a class="index-entry-id" id="index-matching-failure_002c-in-scanf"></a>
</p>
<p>The formatted input functions are not used as frequently as the
formatted output functions. Partly, this is because it takes some care
to use them properly. Another reason is that it is difficult to recover
from a matching error.
</p>
<p>The specific flags and modifiers that are permitted in the template string
and their interpretation are all described in more detail in the following
sections.
</p>
</div>
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