Fragment

Notation

The fragment identifier in a URL provides further refinement of the specification of the resource, including additional identifying information. It provides directions to a secondary resource related to such main resource, such as the section in an article or a time-point in a video.

As usual, its semantics vary depending on the scheme, authority, path, and media type of the resource. In HTML, fragments are used as internal page references. This usage is called a "named anchor," referring to a section within a web page.

The URL below contains the fragment "section2":

https://www.example.com/index.html#section2
\____/\_______________/\_________/\_______/
scheme    authority       path     fragment

A fragment appearing in a URL is always preceded by the number sign ('#'). A This makes a URL with a fragment of zero length distinguishable from a URL with no fragment.

The fragment grammar is defined as follows:

Table 1.25. Fragment BNF

fragment        = *( pchar / "/" / "?" )

relative-ref    = relative-part [ "?" query ] [ "#" fragment ]

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

URI-reference   = URI / relative-ref

Member Functions

The functions for inspecting the fragment in a url_view are as follows:

Table 1.26. Fragment Observers

Function	Description
`has_fragment`	Return true if a fragment is present
`encoded_fragment`	Return the fragment as a percent-encoded string.
`fragment`	Return the fragment as a string with percent-decoding applied.

Observers

Analogous to other components, the functions encoded_fragment and fragment can be used to obtain the fragment from a url_view:

Code	Output
urls::string_view s = "https://www.example.com/index.html#section%202"; urls::url_view u = urls::parse_uri(s).value(); std::cout << u << "\n" "has fragment: " << u.has_fragment() << "\n" "encoded fragment: " << u.encoded_fragment() << "\n" "fragment: " << u.fragment() << "\n";	https://www.example.com/index.html#section%202 has fragment: 1 encoded fragment: section%202 fragment: section 2

Code

Output

urls::string_view s = "https://www.example.com/index.html#section%202";
urls::url_view u = urls::parse_uri(s).value();
std::cout << u << "\n"
          "has fragment:     " << u.has_fragment()     << "\n"
          "encoded fragment: " << u.encoded_fragment() << "\n"
          "fragment:         " << u.fragment()         << "\n";

https://www.example.com/index.html#section%202
has fragment:     1
encoded fragment: section%202
fragment:         section 2

These functions do not throw. If the URL has no fragment, encoded_fragment returns an empty string. The function has_fragment can be used to determine whether this empty string means there is no fragment or an empty fragment string in the URL.

Code	Output
urls::string_view s = "https://www.example.com/index.html#"; urls::url_view u = urls::parse_uri(s).value(); std::cout << u << "\n" "has fragment: " << u.has_fragment() << "\n" "encoded fragment: " << u.encoded_fragment() << "\n" "fragment: " << u.fragment() << "\n";	https://www.example.com/index.html# has fragment: 1 encoded fragment: fragment:
urls::string_view s = "https://www.example.com/index.html"; urls::url_view u = urls::parse_uri(s).value(); std::cout << u << "\n" "has fragment: " << u.has_fragment() << "\n" "encoded fragment: " << u.encoded_fragment() << "\n" "fragment: " << u.fragment() << "\n";	https://www.example.com/index.html has fragment: 0 encoded fragment: fragment:

Code

Output

urls::string_view s = "https://www.example.com/index.html#";
urls::url_view u = urls::parse_uri(s).value();
std::cout << u << "\n"
          "has fragment:     " << u.has_fragment()     << "\n"
          "encoded fragment: " << u.encoded_fragment() << "\n"
          "fragment:         " << u.fragment()         << "\n";

https://www.example.com/index.html#
has fragment:     1
encoded fragment:
fragment:

urls::string_view s = "https://www.example.com/index.html";
urls::url_view u = urls::parse_uri(s).value();
std::cout << u << "\n"
          "has fragment:     " << u.has_fragment()     << "\n"
          "encoded fragment: " << u.encoded_fragment() << "\n"
          "fragment:         " << u.fragment()         << "\n";

https://www.example.com/index.html
has fragment:     0
encoded fragment:
fragment:

Use Cases

URL fragments are usually interpreted as a single string.

Component	Value
URL	`https://www.example.com/index.html#section%202`
Has Fragment	Yes
Encoded Fragment	`section%202`
Fragment	`section 2`

The URL fragment might also be empty or absent.

Component	Value
URL	`https://www.example.com/index.html#`
Has Fragment	Yes
Encoded Fragment	(empty)
Fragment	(empty)

Component	Value
URL	`https://www.example.com/index.html`
Has Fragment	No
Encoded Fragment	(No fragment)
Fragment	(No fragment)

The URL reserved characters :, @, ?, and / may appear unencoded with URL fragments, as they are not ambiguous with other URL components.

Component	Value
URL	`https://www.example.com/index.html#code%20:a@b?c/d`
Has Fragment	Yes
Encoded Fragment	`code%20:a@b?c/d`
Fragment	`code :a@b?c/d`