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Pointers And Memory - Contents


How Are Pointers Implemented In The Machine?

A D V E R T I S E M E N T

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    The short explanation is that every area of memory in the machine has a numeric address like 1000 or 20452. A pointer to an area of memory is really just an integer which is storing the address of that area of memory. The dereference operation looks at the address, and goes to that area of memory to retrieve the pointee stored there. Pointer assignment just copies the numeric address from one pointer to another. The NULL value is generally just the numeric address 0 the computer just never allocates a pointee at 0 so that address can be used to represent NULL. A bad pointer is really just a pointer which contains a random address just like an uninitialized int variable which starts out with a random int value. The pointer has not yet been assigned the specific address of a valid pointee. This is why dereference operations with bad pointers are so unpredictable. They operate on whatever random area of memory they happen to have the address of.

    The Term "Reference"The word "reference" means almost the same thing as the word "pointer". The difference is that "reference" tends to be used in a discussion of pointer issues which is not specific to any particular language or implementation. The word "pointer" connotes the common C/C++ implementation of pointers as addresses. The word "reference" is also used in the phrase "reference parameter" which is a technique which uses pointer parameters for twoway communication between functions this technique is the subject of Section 3.


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