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Storing the result of reference (&) operator in reference data typed variables

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• Assigning a reference value to a reference variable
  • Recall that:

    The reference operator & "computes" (returns) the address of a variable: int a = 7; &a returns: the address of the variable a Note: Because the variable a is of the type int, the address &a is an address of an int typed variable !!! We have just learned how to define a variable where you can store an address of an int typed variable: int *p ;

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  • So now it should obvious that you can assign a reference value to a reference typed variables:

    int a = 7; // an int typed variable // &a = the address of a int typed variable int *p; // p can hold an address of an int typed variable // Therefore: p can store &a !!! p = &a; // Store the address of the int type variable a in p

    The result of the assignment statement p = &a is graphically depicted in the following diagram (assuming the the variable a is stored at address 4000 in memory):

    In other words:

    The statement p = &a will make the reference variable p point to the int typed variable a

    We will learn to use a reference variable in the next webpage

    Before we do this, I need to show you an important fact about reference variables first - see below.

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• Important: reference variable must point to the same type of variables as themselves
  • Very important fact:

    int *p; // p can only point to an int typed variable float *q; // q can only point to a float typed variable etc !

    Example: this assignment will cause an compile error:

    #include <stdio.h> int main(int argc, char *argv[]) { int x = 4; float y = 88; int *p; float *q; p = &x; // int ref p points to int variable x - OK q = &y; // float ref q points to float variable y - OK p = &y; // int ref p points to float variable y - Error q = &x; // float ref q points to int variable x - Error }

    Compiler messages:

    cs255-1@aruba (5555)> gcc ref-var3.c ref-var3.c:15:7: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types] p = &y; // int ref p points to float variable y - Error ^ ref-var3.c:16:7: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types] q = &x; // float ref q points to int variable x - Error ^

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  • Example Program: (Demo above code)                                                
    • Prog file: /home/cs255001/demo/C/set2/ref-var3.c

    How to run the program:

    To compile:   gcc ref-var3.c          Check error messages