:relfileprefix: ../../../
[#7113C6D67A485E67D80B42BE0BE89DC4EA88734E]

= Function url_view_base::persist

pass:v,q[Return a shared, persistent copy of the url]


== Synopsis

Declared in header `</boost/url/url_view_base.hpp#L297[boost/url/url_view_base.hpp,window=blank_]>`

[source,cpp,subs="verbatim,macros,-callouts"]
----
shared_ptr<const xref:boost/urls/url_view.adoc[url_view]>
persist() const;
----

== Description

pass:v,q[This function returns a read-only copy of] pass:v,q[the url, with shared lifetime. The returned]
pass:v,q[value owns (persists) the underlying string.]
pass:v,q[The algorithm used to create the value]
pass:v,q[minimizes the number of individual memory]
pass:v,q[allocations, making it more efficient than]
pass:v,q[when using direct standard library functions.]

=== Example
[,cpp]
----
std::shared_ptr< url_view const > sp;
{
    std::string s( "http://example.com" );
    url_view u( s );                        // u references characters in s

    assert( u.data() == s.data() );         // same buffer

    sp = u.persist();

    assert( sp->data() != s.data() );       // different buffer
    assert( sp->buffer() == s);             // same contents

    // s is destroyed and thus u
    // becomes invalid, but sp remains valid.
}
----

=== Complexity
pass:v,q[Linear in `this->size()`.]

=== Exception Safety
pass:v,q[Calls to allocate may throw.]



== Return Value

* `shared_ptr`