[#boost-urls-grammar-alnum_chars]
= xref:boost.adoc[boost]::xref:boost/urls.adoc[urls]::xref:boost/urls/grammar.adoc[grammar]::alnum&lowbar;chars
:relfileprefix: ../../../
:mrdocs:


The set of letters and digits

== Synopsis


Declared in `&lt;https://www.github.com/boostorg/url/blob/develop/include/boost/url/grammar/alnum_chars.hpp#L118[boost&sol;url&sol;grammar&sol;alnum&lowbar;chars&period;hpp]&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
constexpr &sol;&ast; implementation-defined &ast;&sol;::xref:boost/urls/grammar/implementation_defined/alnum_chars_t.adoc[alnum&lowbar;chars&lowbar;t] alnum&lowbar;chars = &lcub;&rcub;;
----

== Description



=== Example

Character sets are used with rules and the    functions xref:boost/urls/grammar/find_if.adoc[find&lowbar;if] and xref:boost/urls/grammar/find_if_not.adoc[find&lowbar;if&lowbar;not]&period;

[,cpp]
----
system::result< core::string_view > = parse( "Johnny42", token_rule( alnumchars ) );
----

=== BNF

[,cpp]
----
ALNUM       = ALPHA / DIGIT

ALPHA       = %x41-5A / %x61-7A
            ; A-Z / a-z

DIGIT       = %x30-39
            ; 0-9
----

=== Specification

* link:https://datatracker.ietf.org/doc/html/rfc5234#appendix-B.1[B&period;1&period; Core Rules (rfc5234)]



== See Also


xref:boost/urls/grammar/find_if.adoc[find&lowbar;if],        xref:boost/urls/grammar/find_if_not.adoc[find&lowbar;if&lowbar;not],        xref:boost/urls/grammar/parse-02.adoc[parse],        xref:boost/urls/grammar/token_rule.adoc[token&lowbar;rule]&period;






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