:relfileprefix: ../../../
[#ACDEA9F7F68B0112FD4BD827D3693E33E8F6D6AF]

= Function url_view_base::zone_id

pass:v,q[Return the IPv6 Zone ID]


== Synopsis

Declared in header `</boost/url/url_view_base.hpp#L1406[boost/url/url_view_base.hpp,window=blank_]>`

[source,cpp,subs="verbatim,macros,-callouts"]
----
template<class StringToken = xref:boost/urls/string_token.adoc[string_token]::xref:boost/urls/string_token/return_string.adoc[return_string]>
StringToken::result_type
zone_id(StringToken&& token) const;
----

== Description

pass:v,q[If the host type is] xref:boost/urls/host_type/ipv6.adoc[host_type::ipv6,]
pass:v,q[this function returns the Zone ID as]
pass:v,q[a string. Otherwise an empty string is returned.]
pass:v,q[Any percent-escapes in the string are]
pass:v,q[decoded first.]

=== Example
[,cpp]
----
assert( url_view( "http://[fe80::1%25eth0]/" ).zone_id() == "eth0" );
----

=== Complexity
pass:v,q[Linear in `this->encoded_zone_id().size()`.]

=== Exception Safety
pass:v,q[Calls to allocate may throw.]

=== BNF
[,cpp]
----
host        = IP-literal / IPv4address / reg-name

IP-literal = "[" ( IPv6address / IPv6addrz / IPvFuture  ) "]"

ZoneID = 1*( unreserved / pct-encoded )

IPv6addrz = IPv6address "%25" ZoneID
----

=== Specification

* link:https://datatracker.ietf.org/doc/html/rfc6874[Representing IPv6 Zone Identifiers in Address Literals and Uniform Resource Identifiers]



== Return Value

* `result_type` 


== Parameters

|===
| Name | Type 

| *token*
| ``

|===