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


Rule for query

== Synopsis


Declared in `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/rfc/query_rule.hpp#L110[boost/url/rfc/query_rule.hpp]>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
constexpr /* implementation-defined */::xref:boost/urls/implementation_defined/query_rule_t.adoc[query_rule_t] query_rule = {};
----

== Description



=== Value Type

[,cpp]
----
using value_type = params_encoded_view;
----

=== Example

Rules are used with the function xref:boost/urls/grammar/parse-02.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

* link:https://datatracker.ietf.org/doc/html/rfc3986#section-3.4[3&period;4&period; Query (rfc3986)]



== See Also


xref:boost/urls/grammar/parse-02.adoc[grammar&colon;&colon;parse],        xref:boost/urls/params_encoded_view.adoc[params&lowbar;encoded&lowbar;view]&period;






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