:relfileprefix: ../../../
[#boost-urls-grammar-hexdig_chars]

== xref:boost.adoc[pass:[boost]]::xref:boost/urls.adoc[pass:[urls]]::xref:boost/urls/grammar.adoc[pass:[grammar]]::hexdig_chars


The set of hexadecimal digits


=== Synopsis

Declared in header `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/grammar/hexdig_chars.hpp#L136[boost/url/grammar/hexdig_chars.hpp,window=blank_]>`

[source,cpp,subs="verbatim,macros,-callouts"]
----
constexpr
pass:q[_implementation-defined_] hexdig_chars = {};
----

=== Description


=== Character sets are used with rules and the

functions
xref:boost/urls/grammar/find_if.adoc[find_if]
and
xref:boost/urls/grammar/find_if_not.adoc[find_if_not]
.
[,cpp]
----
system::result< core::string_view > rv = parse( "8086FC19", token_rule( hexdig_chars ) );
----
[,cpp]
----
HEXDIG      = DIGIT
            / "A" / "B" / "C" / "D" / "E" / "F"
            / "a" / "b" / "c" / "d" / "e" / "f"
----
[NOTE]

The RFCs are inconsistent on the case
sensitivity of hexadecimal digits. Existing
uses suggest case-insensitivity is a de-facto
standard.

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

* link:https://datatracker.ietf.org/doc/html/rfc7230#section-1.2[1.2. Syntax Notation (rfc7230)]

* link:https://datatracker.ietf.org/doc/html/rfc5952#section-2.3[2.3. Uppercase or Lowercase (rfc5952)]

* link:https://datatracker.ietf.org/doc/html/rfc5952#section-4.3[4.3. Lowercase (rfc5952)]



=== See Also


xref:boost/urls/grammar/find_if.adoc[find_if]
,
xref:boost/urls/grammar/find_if_not.adoc[find_if_not]
,
xref:boost/urls/grammar/hexdig_value.adoc[hexdig_value]
,
xref:boost/urls/grammar/parse-02.adoc[parse]
,
xref:boost/urls/grammar/token_rule.adoc[token_rule]
.