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Remember
that with data hiding and encapsulation, we
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force
clients to manipulate private data through public
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member
functions. By declaring friends, we allow non-
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member
functions or member functions of other classes
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access
to private data.
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A
class can declare another class to be a friend.
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When
we do this, the first class gives all member
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functions
of the second class permission to access all of its
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protected
and private information (not the other way
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around;
a class cannot declare itself a friend of another
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class).
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