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

Set the scheme

== Synopsis

Declared in `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/url_base.hpp#L281[boost/url/url_base.hpp]>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
xref:boost/urls/url_base.adoc[url_base]&
set_scheme_id(xref:boost/urls/scheme.adoc[urls::scheme] id);
----

== Description

This function sets the scheme to the specified known xref:boost/urls/scheme.adoc[`urls::scheme`] id, which may not be xref:boost/urls/scheme.adoc[`scheme::unknown`] or else an exception is thrown. If the id is xref:boost/urls/scheme.adoc[`scheme::none`], this function behaves as if xref:boost/urls/url_base/remove_scheme.adoc[`remove_scheme`] were called.

== Example
[,cpp]
----
assert( url( "http://example.com/echo.cgi" ).set_scheme_id( scheme::wss ).buffer() == "wss://example.com/echo.cgi" );
----
== Complexity
Linear in `this‐>size()`.

== Exception Safety
Strong guarantee. Calls to allocate may throw. Exceptions thrown on invalid input.

== Specification
* https://datatracker.ietf.org/doc/html/rfc3986#section-3.1[]

== Exceptions

[cols=2]
|===
| Name
| Thrown on
| `system_error`
| The scheme is invalid.
|===

== Return Value

`*this`

== Parameters

[cols=2]
|===
| Name
| Description
| *id*
| The scheme to set.
|===


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