:relfileprefix: ../../../
[#boost-urls-url_base-set_host_address]

= xref:boost.adoc[pass:[boost]]::xref:boost/urls.adoc[pass:[urls]]::xref:boost/urls/url_base.adoc[pass:[url_base]]::set_host_address


Set the host to an address


== Synopsis

Declared in header `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/url_base.hpp#L1105[boost/url/url_base.hpp,window=blank_]>`

[source,cpp,subs="verbatim,macros,-callouts"]
----
xref:boost/urls/url_base.adoc[url_base]&
set_host_address(core::string_view s);
----

== Description


Depending on the contents of the passed
string, this function sets the host:

* If the string is a valid IPv4 address,
then the host is set to the address.
The host type is
xref:boost/urls/host_type/ipv4.adoc[host_type::ipv4]
.

* If the string is a valid IPv6 address,
then the host is set to that address.
The host type is
xref:boost/urls/host_type/ipv6.adoc[host_type::ipv6]
.

* If the string is a valid IPvFuture,
then the host is set to that address.
The host type is
xref:boost/urls/host_type/ipvfuture.adoc[host_type::ipvfuture]
.

* Otherwise, the host name is set to
the string, which may be empty.
Reserved characters in the string are
percent-escaped in the result.
The host type is
xref:boost/urls/host_type/name.adoc[host_type::name]
.

In all cases, when this function returns,
the URL contains an authority.

=== Example
[,cpp]
----
assert( url( "http://www.example.com" ).set_host_address( "127.0.0.1" ).buffer() == "http://127.0.0.1" );
----

=== Postconditions
[,cpp]
----
this->has_authority() == true
----

=== Complexity

Linear in `s.size()`.

=== Exception Safety

Strong guarantee.
Calls to allocate may throw.

=== BNF
[,cpp]
----
IPv4address = dec-octet "." dec-octet "." dec-octet "." dec-octet

dec-octet   = DIGIT                 ; 0-9
            / %x31-39 DIGIT         ; 10-99
            / "1" 2DIGIT            ; 100-199
            / "2" %x30-34 DIGIT     ; 200-249
            / "25" %x30-35          ; 250-255

IPv6address =                            6( h16 ":" ) ls32
            /                       "::" 5( h16 ":" ) ls32
            / [               h16 ] "::" 4( h16 ":" ) ls32
            / [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
            / [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
            / [ *3( h16 ":" ) h16 ] "::"    h16 ":"   ls32
            / [ *4( h16 ":" ) h16 ] "::"              ls32
            / [ *5( h16 ":" ) h16 ] "::"              h16
            / [ *6( h16 ":" ) h16 ] "::"

ls32        = ( h16 ":" h16 ) / IPv4address
            ; least-significant 32 bits of address

h16         = 1*4HEXDIG
            ; 16 bits of address represented in hexadecimal

IPvFuture     = "v" 1*HEXDIG "." 1*( unreserved / sub-delims / ":" )

reg-name    = *( unreserved / pct-encoded / "-" / ".")
----

=== Specification

* link:https://en.wikipedia.org/wiki/IPv4[IPv4 (Wikipedia)]

* link:https://datatracker.ietf.org/doc/html/rfc4291[IP Version 6 Addressing Architecture (rfc4291)]

* link:https://datatracker.ietf.org/doc/html/rfc3986#section-3.2.2[            3.2.2. Host (rfc3986)]





== Parameters

|===
| Name | Description 

| *s*
| 
The string to set.

|===




== See Also


xref:boost/urls/url_base/set_encoded_host.adoc[set_encoded_host]
,
xref:boost/urls/url_base/set_encoded_host_address.adoc[set_encoded_host_address]
,
xref:boost/urls/url_base/set_encoded_host_name.adoc[set_encoded_host_name]
,
xref:boost/urls/url_base/set_host.adoc[set_host]
,
xref:boost/urls/url_base/set_host_address.adoc[set_host_address]
,
xref:boost/urls/url_base/set_host_ipv4.adoc[set_host_ipv4]
,
xref:boost/urls/url_base/set_host_ipv6.adoc[set_host_ipv6]
,
xref:boost/urls/url_base/set_host_ipvfuture.adoc[set_host_ipvfuture]
,
xref:boost/urls/url_base/set_host_name.adoc[set_host_name]
.