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<a name="Character-Arrays"></a>
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<a name="Character-Arrays-1"></a>
<h3 class="section">5.2 Character Arrays</h3>
<p>The string representation used by Octave is an array of characters, so
internally the string <code>"dddddddddd"</code> is actually a row vector
of length 10 containing the value 100 in all places (100 is the ASCII code of
<code>"d"</code>). This lends itself to the obvious generalization to character
matrices. Using a matrix of characters, it is possible to represent a
collection of same-length strings in one variable. The convention used in
Octave is that each row in a character matrix is a separate string, but letting
each column represent a string is equally possible.
</p>
<p>The easiest way to create a character matrix is to put several strings
together into a matrix.
</p>
<div class="example">
<pre class="example">collection = [ "String #1"; "String #2" ];
</pre></div>
<p>This creates a 2-by-9 character matrix.
</p>
<p>The function <code>ischar</code> can be used to test if an object is a character
matrix.
</p>
<a name="XREFischar"></a><dl>
<dt><a name="index-ischar"></a><em></em> <strong>ischar</strong> <em>(<var>x</var>)</em></dt>
<dd><p>Return true if <var>x</var> is a character array.
</p>
<p><strong>See also:</strong> <a href="Predicates-for-Numeric-Objects.html#XREFisfloat">isfloat</a>, <a href="Integer-Data-Types.html#XREFisinteger">isinteger</a>, <a href="Predicates-for-Numeric-Objects.html#XREFislogical">islogical</a>, <a href="Predicates-for-Numeric-Objects.html#XREFisnumeric">isnumeric</a>, <a href="#XREFisstring">isstring</a>, <a href="Cell-Arrays-of-Strings.html#XREFiscellstr">iscellstr</a>, <a href="Built_002din-Data-Types.html#XREFisa">isa</a>.
</p></dd></dl>
<a name="XREFisstring"></a><dl>
<dt><a name="index-isstring"></a><em></em> <strong>isstring</strong> <em>(<var>s</var>)</em></dt>
<dd><p>Return true if <var>s</var> is a string array.
</p>
<p>A string array is a data type that stores strings (row vectors of
characters) at each element in the array. It is distinct from character
arrays which are N-dimensional arrays where each element is a single 1x1
character. It is also distinct from cell arrays of strings which store
strings at each element, but use cell indexing ‘<samp>{}</samp>’ to access
elements rather than string arrays which use ordinary array indexing
‘<samp>()</samp>’.
</p>
<p>Programming Note: Octave does not yet implement string arrays so this
function will always return false.
</p>
<p><strong>See also:</strong> <a href="#XREFischar">ischar</a>, <a href="Cell-Arrays-of-Strings.html#XREFiscellstr">iscellstr</a>, <a href="Predicates-for-Numeric-Objects.html#XREFisfloat">isfloat</a>, <a href="Integer-Data-Types.html#XREFisinteger">isinteger</a>, <a href="Predicates-for-Numeric-Objects.html#XREFislogical">islogical</a>, <a href="Predicates-for-Numeric-Objects.html#XREFisnumeric">isnumeric</a>, <a href="Built_002din-Data-Types.html#XREFisa">isa</a>.
</p></dd></dl>
<p>To test if an object is a string (i.e., a 1xN row vector of
characters and not a character matrix) you can use the <code>ischar</code> function
in combination with the <code>isrow</code> function as in the following example:
</p>
<div class="example">
<pre class="example">ischar (collection)
⇒ 1
ischar (collection) && isrow (collection)
⇒ 0
ischar ("my string") && isrow ("my string")
⇒ 1
</pre></div>
<p>One relevant question is, what happens when a character matrix is
created from strings of different length. The answer is that Octave
puts blank characters at the end of strings shorter than the longest
string. It is possible to use a different character than the
blank character using the <code>string_fill_char</code> function.
</p>
<a name="XREFstring_005ffill_005fchar"></a><dl>
<dt><a name="index-string_005ffill_005fchar"></a><em><var>val</var> =</em> <strong>string_fill_char</strong> <em>()</em></dt>
<dt><a name="index-string_005ffill_005fchar-1"></a><em><var>old_val</var> =</em> <strong>string_fill_char</strong> <em>(<var>new_val</var>)</em></dt>
<dt><a name="index-string_005ffill_005fchar-2"></a><em></em> <strong>string_fill_char</strong> <em>(<var>new_val</var>, "local")</em></dt>
<dd><p>Query or set the internal variable used to pad all rows of a character
matrix to the same length.
</p>
<p>The value must be a single character and the default is <code>" "</code> (a
single space). For example:
</p>
<div class="example">
<pre class="example">string_fill_char ("X");
[ "these"; "are"; "strings" ]
⇒ "theseXX"
"areXXXX"
"strings"
</pre></div>
<p>When called from inside a function with the <code>"local"</code> option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
</p></dd></dl>
<p>This shows a problem with character matrices. It simply isn’t possible to
represent strings of different lengths. The solution is to use a cell array of
strings, which is described in <a href="Cell-Arrays-of-Strings.html#Cell-Arrays-of-Strings">Cell Arrays of Strings</a>.
</p>
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