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What does << mean in C++?

What does the following macro mean, especially the << sign:

#define hello(x) (( int64 ) floor( (double) x ) << 32)


Aug 8 '06
10 48360
On 8 Aug 2006 14:35:13 -0700, "peter koch"
<pe************ ***@gmail.comwr ote in comp.lang.c++:
Thierry Lam skrev:
What does the following macro mean, especially the << sign:

#define hello(x) (( int64 ) floor( (double) x ) << 32)


In C++, << is normally the stream-operator - used e.g. for outputting
variables. In low-level code it can also be used for bitshifting -
which previously was used sometimes for optimising
multiplication/division. Today, you gain nothing in speed and you
should avoid usage of the operator for stuff of this type.
In the example above, to the best of my knowledge the result of the
macro is undefined as shifts of an int64 is implementation-defined. (Of
course - so is int64).
Very misleading, bordering on incorrect. In the C++ language, the <<
operator is specifically defined as the bit-wise left shift operator
for integral types. It always has been, it always will be, and it
cannot be changed.

It is common practice to overload this operator for user-defined types
as a stream insertion operator when applied to a reference to a
stream. This overload is supplied by several stream classes included
in the standard C++ library. But it does not change the original
meaning of the operator.

Jack Klein
Home: http://JK-Technology.Com
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Aug 8 '06 #11

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