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


A query parameter

== Synopsis


Declared in `&lt;https://www.github.com/boostorg/url/blob/develop/include/boost/url/param.hpp#L75[boost&sol;url&sol;param&period;hpp]&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
struct param;
----

== Member Functions

[cols=2]
|===
| Name | Description 

| xref:boost/urls/param/operator_ptr.adoc[`operator&hyphen;&gt;`] 
| Arrow support

| xref:boost/urls/param/operator_assign.adoc[`operator&equals;`] 
| Assignment


| xref:boost/urls/param/2constructor.adoc[`param`]         [.small]#[constructor]#
| Aggregate construction

Constructor


|===
== Data Members

[cols=2]
|===
| Name | Description 

| xref:boost/urls/param/has_value.adoc[`has&lowbar;value`] 
| True if a value is present

| xref:boost/urls/param/key.adoc[`key`] 
| The key

| xref:boost/urls/param/value.adoc[`value`] 
| The value

|===



== Description


Objects of this type represent a single key    and value pair in a query string where a key    is always present and may be empty, while the    presence of a value is indicated by    xref:boost/urls/param/has_value.adoc[has&lowbar;value] equal to true&period;    An empty value is distinct from no value&period;

Depending on where the object was obtained,    the strings may or may not contain percent    escapes&period;

For most usages, key comparisons are    case&hyphen;sensitive and duplicate keys in    a query are possible&period; However, it is    the authority that has final control    over how the query is interpreted&period;


=== BNF

[,cpp]
----
query-params    = query-param *( "&" query-param )
query-param     = key [ "=" value ]
key             = *qpchar
value           = *( qpchar / "=" )
----

=== Specification

* link:https://en.wikipedia.org/wiki/Query_string[Query string (Wikipedia)]



== See Also


xref:boost/urls/param_view.adoc[param&lowbar;view],        xref:boost/urls/param_pct_view.adoc[param&lowbar;pct&lowbar;view]&period;






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