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Document argument swapping in [s]printf format string

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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@45073 c90b9560-bf6c-de11-be94-00142212c4b1
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Rasmus Lerdorf 2001-04-09 16:00:17 +00:00
parent 11c0f75b36
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functions/strings.xml
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@ -1915,6 +1915,48 @@ soundex ("Lukasiewicz") == soundex ("Lissajous") == 'L222';
</listitem>
</orderedlist>
</para>
<para>
As of PHP version 4.0.6 the format string supports argument
numbering/swapping. Here is an example:
<example>
<title>Argument swapping</title>
<programlisting role="php">
$format = "There are %d monkeys in the %s";
printf($format,$num,$location);
</programlisting>
</example>
This might output, "There are 5 monkeys in the tree". But imagine we are
creating a format string in a separate file, commonly because we would like to
internationalize it and we rewrite it as:
<example>
<title>Argument swapping</title>
<programlisting role="php">
$format = "The %s contains %d monkeys";
printf($format,$num,$location);
</programlisting>
</example>
We now have a problem. The order of the placeholders in the format string
does not match the order of the arguments in the code. We would like to
leave the code as is and simply indicate in the format string which arguments
the placeholders refer to. We would write the format string like this
instead:
<example>
<title>Argument swapping</title>
<programlisting role="php">
$format = "The %2\$s contains %1\$d monkeys";
printf($format,$num,$location);
</programlisting>
</example>
An added benefit here is that you can repeat the placeholders without
adding more arguments in the code. For example:
<example>
<title>Argument swapping</title>
<programlisting role="php">
$format = "The %2\$s contains %1\$d monkeys. That's a nice %2\$s full of %1\$d monkeys.";
printf($format,$num,$location);
</programlisting>
</example>
</para>
<simpara>
See also: <function>printf</function>, <function>sscanf</function>,
<function>fscanf</function>, and <function>number_format</function>.