:relfileprefix: ../../../
[#boost-urls-params_encoded_base-contains]

= xref:boost.adoc[pass:[boost]]::xref:boost/urls.adoc[pass:[urls]]::xref:boost/urls/params_encoded_base.adoc[pass:[params_encoded_base]]::contains


Return true if a matching key exists


== Synopsis

Declared in header `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/params_encoded_base.hpp#L267[boost/url/params_encoded_base.hpp,window=blank_]>`

[source,cpp,subs="verbatim,macros,-callouts"]
----
bool
contains(
    xref:boost/urls/pct_string_view.adoc[pct_string_view] key,
    xref:boost/urls/ignore_case_param.adoc[ignore_case_param] ic = = {}) const noexcept;
----

== Description


This function examines the parameters
in the container to find a match for
the specified key,
which may contain percent escapes.
The comparison is performed as if all
escaped characters were decoded first.

=== Example
[,cpp]
----
assert( url_view( "?first=John&last=Doe" ).encoded_params().contains( "first" ) );
----

=== Complexity

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

=== Exception Safety

Exceptions thrown on invalid input.



== Exceptions

|===
| Name | Thrown on

| `system_error`
| 
`key` contains an invalid percent-encoding.

|===



== Parameters

|===
| Name | Description 

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

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

|===