[#boost-urls-params_encoded_base-contains]
= xref:boost.adoc[boost]::xref:boost/urls.adoc[urls]::xref:boost/urls/params_encoded_base.adoc[params_encoded_base]::contains
:relfileprefix: ../../../
:mrdocs:

Return true if a matching key exists

== Synopsis

Declared in `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/params_encoded_base.hpp#L305[boost/url/params_encoded_base.hpp]>`

[source,cpp,subs="verbatim,replacements,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‐>buffer().size()`.

== Exception Safety
Exceptions thrown on invalid input.

== Exceptions

[cols=2]
|===
| Name
| Thrown on
| `system_error`
| `key` contains an invalid percent‐encoding.
|===

== Return Value

`true` if a matching key exists.

== Parameters

[cols=2]
|===
| 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.
|===


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