[#boost-urls-url_base-set_host_address]
= xref:boost.adoc[boost]::xref:boost/urls.adoc[urls]::xref:boost/urls/url_base.adoc[url&lowbar;base]::set&lowbar;host&lowbar;address
:relfileprefix: ../../../
:mrdocs:

Set the host to an address

== Synopsis

Declared in `&lt;https://www.github.com/boostorg/url/blob/develop/include/boost/url/url_base.hpp#L1127[boost&sol;url&sol;url&lowbar;base&period;hpp]&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
xref:boost/urls/url_base.adoc[url&lowbar;base]&
set&lowbar;host&lowbar;address(core::string&lowbar;view s);
----

== Description

Depending on the contents of the passed string, this function sets the host&colon;

* If the string is a valid IPv4 address, then the host is set to the address&period; The host type is `host&lowbar;type&colon;&colon;ipv4`&period;
* If the string is a valid IPv6 address, then the host is set to that address&period; The host type is `host&lowbar;type&colon;&colon;ipv6`&period;
* If the string is a valid IPvFuture, then the host is set to that address&period; The host type is `host&lowbar;type&colon;&colon;ipvfuture`&period;
* Otherwise, the host name is set to the string, which may be empty&period; Reserved characters in the string are percent&hyphen;escaped in the result&period; The host type is `host&lowbar;type&colon;&colon;name`&period;

In all cases, when this function returns, the URL contains an authority&period;

== 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&period;size()`&period;

== Exception Safety
Strong guarantee&period; Calls to allocate may throw&period;

== 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
* https://en.wikipedia.org/wiki/IPv4[]
* https://datatracker.ietf.org/doc/html/rfc4291[]
* https://datatracker.ietf.org/doc/html/rfc3986#section-3.2.2[]

== Return Value

`&ast;this`

== Parameters

[cols=2]
|===
| Name
| Description
| *s*
| The string to set&period;
|===

== See Also

xref:boost/urls/url_base/set_encoded_host.adoc[`set&lowbar;encoded&lowbar;host`], xref:boost/urls/url_base/set_encoded_host_address.adoc[`set&lowbar;encoded&lowbar;host&lowbar;address`], xref:boost/urls/url_base/set_encoded_host_name.adoc[`set&lowbar;encoded&lowbar;host&lowbar;name`], xref:boost/urls/url_base/set_host.adoc[`set&lowbar;host`], xref:boost/urls/url_base/set_host_address.adoc[`set&lowbar;host&lowbar;address`], xref:boost/urls/url_base/set_host_ipv4.adoc[`set&lowbar;host&lowbar;ipv4`], xref:boost/urls/url_base/set_host_ipv6.adoc[`set&lowbar;host&lowbar;ipv6`], xref:boost/urls/url_base/set_host_ipvfuture.adoc[`set&lowbar;host&lowbar;ipvfuture`], xref:boost/urls/url_base/set_host_name.adoc[`set&lowbar;host&lowbar;name`]&period;


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