[#boost-urls-url_view_base-scheme_id]
= xref:boost/urls/url_view_base/scheme_id.adoc[boost::urls::url_view_base::scheme_id]
:relfileprefix: ../../../
:mrdocs:

Return the scheme

== Synopsis

Declared in `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/url_view_base.hpp#L454[boost/url/url_view_base.hpp]>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
xref:boost/urls/scheme.adoc[urls::scheme]
scheme_id() const noexcept;
----

== Description

This function returns a value which depends on the scheme in the url:

* If the scheme is a well‐known scheme, corresponding value from the enumeration `urls::scheme` is returned.
* If a scheme is present but is not a well‐known scheme, the value returned is `urls::scheme::unknown`.
* Otherwise, if the scheme is absent the value returned is `urls::scheme::none`.

== Example
[,cpp]
----
assert( url_view( "wss://www.example.com/crypto.cgi" ).scheme_id() == scheme::wss );
----
== Complexity
Constant.

== Exception Safety
Throws nothing.

== BNF
[,cpp]
----
URI             = scheme ":" hier-part [ "?" query ] [ "#" fragment ]

absolute-URI    = scheme ":" hier-part [ "?" query ]

scheme          = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
----
== Specification
* https://datatracker.ietf.org/doc/html/rfc3986#section-3.1[]

== Return Value

The scheme as an enumeration value.

== See Also

xref:boost/urls/url_view_base/has_scheme.adoc[`has_scheme`], xref:boost/urls/url_view_base/scheme.adoc[`scheme`].


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