<s>
In	O
the	O
programming	O
language	O
C++	B-Language
,	O
unordered	B-Language
associative	I-Language
containers	I-Language
are	O
a	O
group	O
of	O
class	O
templates	B-Application
in	O
the	O
C++	B-Language
Standard	I-Language
Library	I-Language
that	O
implement	O
hash	B-Algorithm
table	I-Algorithm
variants	O
.	O
</s>
<s>
Being	O
templates	B-Application
,	O
they	O
can	O
be	O
used	O
to	O
store	O
arbitrary	O
elements	O
,	O
such	O
as	O
integers	O
or	O
custom	O
classes	O
.	O
</s>
<s>
The	O
following	O
containers	O
are	O
defined	O
in	O
the	O
current	O
revision	O
of	O
the	O
C++	B-Language
standard	O
:	O
unordered_set	O
,	O
unordered_map	O
,	O
unordered_multiset	O
,	O
unordered_multimap	O
.	O
</s>
<s>
The	O
unordered	B-Language
associative	I-Language
containers	I-Language
are	O
similar	O
to	O
the	O
associative	B-Application
containers	I-Application
in	O
the	O
C++	B-Language
Standard	I-Language
Library	I-Language
but	O
have	O
different	O
constraints	O
.	O
</s>
<s>
As	O
their	O
name	O
implies	O
,	O
the	O
elements	O
in	O
the	O
unordered	B-Language
associative	I-Language
containers	I-Language
are	O
not	O
ordered	O
.	O
</s>
<s>
The	O
containers	O
can	O
still	O
be	O
iterated	O
through	O
like	O
a	O
regular	O
associative	B-Application
container	I-Application
.	O
</s>
<s>
The	O
first	O
widely	O
used	O
implementation	O
of	O
hash	B-Algorithm
tables	I-Algorithm
in	O
the	O
C++	B-Language
language	I-Language
was	O
hash_map	O
,	O
hash_set	O
,	O
hash_multimap	O
,	O
hash_multiset	O
class	O
templates	B-Application
of	O
the	O
Silicon	O
Graphics	O
(	O
SGI	O
)	O
Standard	B-Application
Template	I-Application
Library	I-Application
(	O
STL	O
)	O
.	O
</s>
<s>
Due	O
to	O
their	O
usefulness	O
,	O
they	O
were	O
later	O
included	O
in	O
several	O
other	O
implementations	O
of	O
the	O
C++	B-Language
Standard	I-Language
Library	I-Language
(	O
e.g.	O
,	O
the	O
GNU	B-Application
Compiler	I-Application
Collection	I-Application
's	O
(	O
GCC	B-Application
)	O
libstdc++	B-Language
and	O
the	O
Visual	B-Application
C++	I-Application
(	O
MSVC	B-Application
)	O
standard	O
library	O
)	O
.	O
</s>
<s>
The	O
hash_*	O
class	O
templates	B-Application
were	O
proposed	O
into	O
C++	B-Language
Technical	I-Language
Report	I-Language
1	I-Language
(	O
C++	B-Language
TR1	I-Language
)	O
and	O
were	O
accepted	O
under	O
names	O
unordered_*	O
.	O
</s>
<s>
Later	O
,	O
they	O
were	O
incorporated	O
into	O
the	O
C++11	B-Language
revision	O
of	O
the	O
C++	B-Language
standard	O
.	O
</s>
<s>
An	O
implementation	O
is	O
also	O
available	O
in	O
the	O
Boost	B-Language
C++	I-Language
Libraries	I-Language
as	O
<boost/unordered_map.hpp>	O
.	O
</s>
<s>
All	O
containers	O
satisfy	O
the	O
requirements	O
of	O
the	O
concept	B-Application
,	O
which	O
means	O
they	O
have	O
begin( )	O
,	O
end( )	O
,	O
size( )	O
,	O
max_size( )	O
,	O
empty( )	O
,	O
and	O
swap( )	O
methods	O
.	O
</s>
<s>
unordered_set( C++11	O
)	O
unordered_map( C++11	O
)	O
unordered_multiset( C++11	O
)	O
unordered_multimap( C++11	O
)	O
Description	O
(	O
constructor	O
)	O
(	O
constructor	O
)	O
(	O
constructor	O
)	O
(	O
constructor	O
)	O
Constructs	O
the	O
container	O
from	O
variety	O
of	O
sources	O
(	O
destructor	O
)	O
(	O
destructor	O
)	O
(	O
destructor	O
)	O
(	O
destructor	O
)	O
Destructs	O
the	O
set	O
and	O
the	O
contained	O
elements	O
operator	O
=	O
operator	O
=	O
operator	O
=	O
operator	O
=	O
Assigns	O
values	O
to	O
the	O
container	O
get_allocator	O
get_allocator	O
get_allocator	O
get_allocator	O
Returns	O
the	O
allocator	O
used	O
to	O
allocate	O
memory	O
for	O
the	O
elements	O
Element	O
access	O
at	O
Accesses	O
specified	O
element	O
with	O
bounds	O
checking	O
.	O
</s>
<s>
emplace	O
emplace	O
emplace	O
emplace	O
Constructs	O
elements	O
in-place	O
(	O
C++11	B-Language
)	O
emplace_hint	O
emplace_hint	O
emplace_hint	O
emplace_hint	O
Constructs	O
elements	O
in-place	O
using	O
a	O
hint	O
(	O
C++11	B-Language
)	O
erase	O
erase	O
erase	O
erase	O
Erases	O
elements	O
.	O
</s>
