:relfileprefix: ../../../
[#boost-urls-params_ref-set-01]

= xref:boost.adoc[pass:[boost]]::xref:boost/urls.adoc[pass:[urls]]::xref:boost/urls/params_ref.adoc[pass:[params_ref]]::set


Set a value


== Synopsis

Declared in header `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/params_ref.hpp#L910[boost/url/params_ref.hpp,window=blank_]>`

[source,cpp,subs="verbatim,macros,-callouts"]
----
xref:boost/urls/params_base/iterator.adoc[iterator]
set(
    core::string_view key,
    core::string_view value,
    xref:boost/urls/ignore_case_param.adoc[ignore_case_param] ic = = {});
----

== Description


This function performs one of two
actions depending on the value of
`this-&gt;contains( key, ic )`.

* If key is contained in the view
then one of the matching elements has
its value changed to the specified value.
The remaining elements with a matching
key are erased. Otherwise,

* If `key` is not contained in the
view, then the function apppends the
param `{ key, value }`.



All iterators are invalidated.

=== Example
[,cpp]
----
url u( "?id=42&id=69" );

u.params().set( "id", "none" );

assert( u.params().count( "id" ) == 1 );
----

=== Postconditions
[,cpp]
----
this->count( key, ic ) == 1 && this->find( key, ic )->value == value
----

=== Complexity

Linear in `this-&gt;url().encoded_query().size()`.

=== Exception Safety

Strong guarantee.
Calls to allocate may throw.




== Return Value


An iterator to the appended
or modified element.



== Parameters

|===
| Name | Description 

| *key*
| 
The key to match.
By default, a case-sensitive
comparison is used.

| *value*
| 
The value to assign. The
empty string still counts as a value.
That is, `has_value` for the element
is true.

| *ic*
| 
An optional parameter. If
the value
xref:boost/urls/ignore_case.adoc[ignore_case]
is passed
here, the comparison is
case-insensitive.

|===