[#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#L290[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


|===
| 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.


|===



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