Pointers And Memory - Contents
A D V E R T I S E M E N T
Make A Drawing
Memory drawings are the key to thinking about pointer code. When you are looking at
code, thinking about how it will use memory at run time....make a quick drawing to work
out your ideas. This article certainly uses drawings to show how pointers work. That's the
way to do it.
Sharing
Two pointers which both refer to a single pointee are said to be "sharing". That two or
more entities can cooperatively share a single memory structure is a key advantage of
pointers in all computer languages. Pointer manipulation is just technique — sharing is
often the real goal. In Section 3 we will see how sharing can be used to provide efficient
communication between parts of a program.
Shallow and Deep Copying
In particular, sharing can enable communication between two functions. One function
passes a pointer to the value of interest to another function. Both functions can access the
value of interest, but the value of interest itself is not copied. This communication is
called "shallow" since instead of making and sending a (large) copy of the value of
interest, a (small) pointer is sent and the value of interest is shared. The recipient needs to
understand that they have a shallow copy, so they know not to change or delete it since it
is shared. The alternative where a complete copy is made and sent is known as a "deep"
copy. Deep copies are simpler in a way, since each function can change their copy
without interfering with the other copy, but deep copies run slower because of all the
copying.
The drawing below shows shallow and deep copying between two functions, A() and B().
In the shallow case, the smiley face is shared by passing a pointer between the two. In the
deep case, the smiley face is copied, and each function gets their own...
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