<s>
In	O
the	O
C	B-Language
programming	I-Language
language	I-Language
,	O
register	B-General_Concept
is	O
a	O
reserved	O
word	O
(	O
or	O
keyword	O
)	O
,	O
type	O
modifier	O
,	O
storage	O
class	O
,	O
and	O
hint	O
.	O
</s>
<s>
The	O
register	B-General_Concept
keyword	O
was	O
deprecated	O
in	O
C++	B-Language
,	O
until	O
it	O
became	O
reserved	O
and	O
unused	O
in	O
C++17	B-Language
.	O
</s>
<s>
It	O
suggests	O
that	O
the	O
compiler	B-Language
stores	O
a	O
declared	O
variable	O
in	O
a	O
CPU	B-General_Concept
register	I-General_Concept
(	O
or	O
some	O
other	O
faster	O
location	O
)	O
instead	O
of	O
in	O
random-access	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
If	O
possible	O
depending	O
on	O
the	O
type	O
of	O
CPU	B-Device
and	O
complexity	O
of	O
the	O
program	O
code	O
,	O
it	O
will	O
optimize	O
access	O
to	O
that	O
variable	O
and	O
hence	O
improve	O
the	O
execution	O
time	O
of	O
a	O
program	O
.	O
</s>
<s>
In	O
C	B-Language
(	O
but	O
not	O
C++	B-Language
where	O
the	O
keyword	O
is	O
essentially	O
ignored	O
)	O
the	O
location	O
of	O
a	O
variable	O
declared	O
with	O
register	B-General_Concept
cannot	O
be	O
accessed	O
,	O
but	O
the	O
sizeof	B-Language
operator	O
can	O
be	O
applied	O
.	O
</s>
<s>
Aside	O
from	O
this	O
limitation	O
,	O
register	B-General_Concept
is	O
essentially	O
meaningless	O
in	O
modern	O
compilers	B-Language
due	O
to	O
optimization	O
which	O
will	O
place	O
variables	O
in	O
a	O
register	B-General_Concept
if	O
appropriate	O
regardless	O
of	O
whether	O
the	O
hint	O
is	O
given	O
.	O
</s>
<s>
For	O
programming	O
of	O
embedded	O
systems	O
register	B-General_Concept
may	O
still	O
be	O
significant	O
;	O
for	O
example	O
the	O
Microchip	O
MPLAB	O
XC32	O
compiler	B-Language
allows	O
the	O
programmer	O
to	O
specify	O
a	O
particular	O
register	B-General_Concept
with	O
the	O
keyword	O
;	O
however	O
,	O
this	O
is	O
discouraged	O
in	O
favor	O
of	O
the	O
compiler	B-Language
's	O
optimizations	O
.	O
</s>
<s>
When	O
used	O
,	O
register	B-General_Concept
is	O
typically	O
for	O
loop	O
counters	O
,	O
or	O
possibly	O
for	O
other	O
very	O
frequently	O
used	O
variables	O
in	O
the	O
code	O
.	O
</s>
