[#boost-urls-unreserved_chars]
= xref:boost.adoc[boost]::xref:boost/urls.adoc[urls]::unreserved&lowbar;chars
:relfileprefix: ../../
:mrdocs:


The unreserved character set

== Synopsis


Declared in `&lt;https://www.github.com/boostorg/url/blob/develop/include/boost/url/rfc/unreserved_chars.hpp#L44[boost&sol;url&sol;rfc&sol;unreserved&lowbar;chars&period;hpp]&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
constexpr xref:boost/urls/grammar.adoc[grammar]::xref:boost/urls/grammar/lut_chars.adoc[lut&lowbar;chars] unreserved&lowbar;chars = &quot;ABCDEFGHIJKLMNOPQRSTUVWXYZ&quot;
    &quot;abcdefghijklmnopqrstuvwxyz&quot;
    &quot;0123456789&quot;
    &quot;&hyphen;&period;&lowbar;&#126;&quot;;
----

== Description



=== Example

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

[,cpp]
----
system::result< decode_view > rv = grammar::parse( "Program%20Files", pct_encoded_rule( unreserved_chars ) );
----

=== BNF

[,cpp]
----
unreserved    = ALPHA / DIGIT / "-" / "." / "_" / "~"
----

=== Specification

* link:https://datatracker.ietf.org/doc/html/rfc3986#section-2.3[2&period;3&period; Unreserved Characters (rfc3986)]



== See Also


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






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