[#boost-urls-query_rule]
= xref:boost/urls/query_rule.adoc[boost::urls::query_rule]
:relfileprefix: ../../
:mrdocs:

Rule for a query string

== Synopsis

Declared in `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/rfc/query_rule.hpp#L70[boost/url/rfc/query_rule.hpp]>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
constexpr /* implementation-defined */ query_rule = {};
----

== Description

== Value Type
[,cpp]
----
using value_type = params_encoded_view;
----
== Example
Rules are used with the function xref:boost/urls/grammar/parse-09.adoc[`grammar::parse`].

[,cpp]
----
system::result< params_encoded_view > rv = grammar::parse( "format=web&id=42&compact", query_rule );
----
== BNF
[,cpp]
----
query           = *( pchar / "/" / "?" )

query-params    = [ query-param ] *( "&" query-param )
query-param     = key [ "=" value ]
key             = *qpchar
value           = *( qpchar / "=" )
qpchar          = unreserved
                / pct-encoded
                / "!" / "$" / "'" / "(" / ")"
                / "*" / "+" / "," / ";"
                / ":" / "@" / "/" / "?"
----
== Specification
* https://datatracker.ietf.org/doc/html/rfc3986#section-3.4[]

== See Also

xref:boost/urls/grammar/parse-09.adoc[`grammar&colon;&colon;parse`], xref:boost/urls/params_encoded_view.adoc[`params&lowbar;encoded&lowbar;view`]&period;


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