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

Non‐owning decoded query parameter view

== Synopsis

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

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
class params_view
    : public xref:boost/urls/params_base.adoc[params_base]
----

== Description

This read‐only range interprets the query string of a URL as bidirectional key/value pairs with percent‐decoding applied on access. It merely references the original character buffer; callers must keep that buffer alive while the view is used.

== Example

[,cpp]
----
url_view u( "?first=John&last=Doe" );

params_view p = u.params();
----
Strings retrieved from the iterators are automatically percent‐decoded.

== Iterator Invalidation

Changes to the underlying character buffer can invalidate iterators which reference it.

== Base Classes

[cols="1,4"]
|===
|Name|Description

| `xref:boost/urls/params_base.adoc[params_base]`
| Decoded query parameter helper base
|===

== Types

[cols="1,4"]
|===
| Name| Description
| xref:boost/urls/params_view/iterator.adoc[`iterator`] 
| A Bidirectional iterator to a query parameter
| xref:boost/urls/params_base/const_iterator.adoc[`const_iterator`] 
| A Bidirectional iterator to a query parameter
| xref:boost/urls/params_base/const_reference.adoc[`const_reference`] 
| The reference type
| xref:boost/urls/params_base/difference_type.adoc[`difference_type`] 
| A signed integer type used to represent differences.
| xref:boost/urls/params_base/reference.adoc[`reference`] 
| The reference type
| xref:boost/urls/params_base/size_type.adoc[`size_type`] 
| An unsigned integer type to represent sizes.
| xref:boost/urls/params_base/value_type.adoc[`value_type`] 
| The value type
|===

== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:boost/urls/params_view/2constructor-06.adoc[`params_view`]         [.small]#[constructor]#
| Constructor
| xref:boost/urls/params_view/operator_assign.adoc[`operator=`] 
| Assignment
| xref:boost/urls/params_base/begin.adoc[`begin`] 
| Return an iterator to the beginning
| xref:boost/urls/params_base/buffer.adoc[`buffer`] 
| Return the referenced character buffer.
| xref:boost/urls/params_base/contains.adoc[`contains`] 
| Return true if a matching key exists
| xref:boost/urls/params_base/count.adoc[`count`] 
| Return the number of matching keys
| xref:boost/urls/params_base/empty.adoc[`empty`] 
| Return true if there are no params
| xref:boost/urls/params_base/end.adoc[`end`] 
| Return an iterator to the end
| xref:boost/urls/params_base/find-0f.adoc[`find`] 
| Find a matching key
| xref:boost/urls/params_base/find_last-04b.adoc[`find_last`] 
| Find a matching key
| xref:boost/urls/params_base/get_or.adoc[`get_or`] 
| Return the value for a key or a fallback
| xref:boost/urls/params_base/size.adoc[`size`] 
| Return the number of params
|===

== Static Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:boost/urls/params_base/max_size.adoc[`max_size`] 
| Return the maximum number of characters possible
|===

== Friends

[cols="1,4"]
|===
|Name|Description

| `xref:boost/urls/params_ref.adoc[boost::urls::params_ref]`
| Mutable decoded query parameter proxy
| `xref:boost/urls/params_encoded_view.adoc[boost::urls::params_encoded_view]`
| Non‐owning encoded query parameter view
| `xref:boost/urls/url_view_base.adoc[boost::urls::url_view_base]`
| Common functionality for containers
|===


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