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In-depth look on the program reference concept

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• Reference: reference to a location in memory
  • You may or may have been exposed to the reference concept in CS170 and CS171.

    But in CS255, we will use a lot of references

    So I want to explain the (program) reference in greater detail before we move on.

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  • Program reference:

    A program reference (a.k.a. pointer ) is "something" that references (= points) to somewhere Examples: 3 pointers or references to different directions In Computer Science, a reference always references to a location in memory Examples: Pointer to memory location 1 Pointer to memory location 4

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  • The computer does not have "pointing fingers" that point to some location in memory

    The reference/pointer is represented in the computer by the value of the address (location) of the memory where the pointer is pointing at

    Examples:

    Reference to the memory location 1	Reference to the memory location 4
    Storing the value 1 in some register/memory cell will remember the memory location 1 The value 1 in the register/memory cell is effectively pointing to the memory location 1	Storing the value 4 in some register/memory cell will remember the memory location 4 The value 4 in the register/memory cell is effectively pointing to the memory location 4

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• Example of a program reference/pointer: the program counter (PC)

  • The program counter (PC) is in fact a reference/pointer

    Example:

    When the program counter (PC) contains the value 44: the program counter (PC) is in fact pointing to the memory location 44: