[#boost-urls-url-set_host-03]
= xref:boost.adoc[boost]::xref:boost/urls.adoc[urls]::xref:boost/urls/url.adoc[url]::set&lowbar;host
:relfileprefix: ../../../
:mrdocs:


Set the host

== Synopsis


Declared in `&lt;https://www.github.com/boostorg/url/blob/develop/include/boost/url/url.hpp#L439[boost&sol;url&sol;url&period;hpp]&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
xref:boost/urls/url.adoc[url]&
set&lowbar;host(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        enclosed in square brackets, 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        address enclosed in square brackets, 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( "127.0.0.1" ).buffer() == "http://127.0.0.1" );
----

=== Postconditions

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

=== Complexity

Linear in `this&hyphen;&gt;size() &plus; s&period;size()`&period;


=== Exception Safety

Strong guarantee&period;        Calls to allocate may throw&period;


=== BNF

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

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

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&period;2&period;2&period; Host (rfc3986)]



== Parameters


|===
| 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_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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