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Predicate uri_query_components/2
Availability::- use_module(library(uri)).(can be autoloaded)
Source[det]uri_query_components(+String, -Query)
[det]uri_query_components(-String, +Query)
Perform encoding and decoding of an URI query string. Query is a list of fully decoded (Unicode) Name=Value pairs. In mode (-,+), query elements of the forms Name(Value) and Name-Value are also accepted to enhance interoperability with the option and pairs libraries. E.g. 
?- uri_query_components(QS, [a=b, c('d+w'), n-'VU Amsterdam']).
QS = 'a=b&c=d%2Bw&n=VU%20Amsterdam'.

?- uri_query_components('a=b&c=d%2Bw&n=VU%20Amsterdam', Q).
Q = [a=b, c='d+w', n='VU Amsterdam'].
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Wouter Beek said (2017-10-28T19:46:56):0 upvotes 0 0 downvotes
Picture of user Wouter Beek.

Be careful when combining this predicate with uri_components/2: if an URI has no query/search component, the following throws an instantiation exception:

uri_components(Uri, uri_components(_, _, _, Query, _),
uri_query_components(String, Query),