Section 5.3 Dereferencing

Section 5.3 Dereferencing#

Adapted from: “Beej’s Guide to C Programming” by Brian (Beej Jorgensen) Hall: Beej’s Guide to C Programming: 5.3 Dereferencing

Brian (Beej Jorgensen) Hall Website

Program that Demonstrates Dereferencing a Pointer#

#include <stdio.h>

int main(void)
{
    int i;
    int *p;  // this is NOT a dereference--this is a type "int*"

    p = &i;  // p now points to i, p holds address of i

    i = 10;  // i is now 10
    *p = 20; // the thing p points to (namely i!) is now 20!!

    printf("i is %d\n", i);   // prints "20"
    printf("i is %d\n", *p);  // "20"! dereference-p is the same as i!
}

Explanation of the Above Code#

The program demonstrates the concept of dereferencing a pointer in C.

  • The variable i is declared as an integer.

  • The variable p is declared as a pointer to an integer (int *p).

  • The address of i is assigned to p using the address-of operator (&).

  • The value of i is set to 10.

  • The value pointed to by p is set to 20 using the dereference operator (*p).

  • Finally, the program prints the value of i and the value pointed to by p, both of which are 20.

  • The dereference operator (*) is used to access the value stored at the address pointed to by p.

  • The output of the program will be:

i is 20
i is 20

  • This shows that dereferencing p gives the same value as i, since p points to i.

Compile and Run Code#

Use Python to Change to Working Directory#

import os
root_dir = os.getcwd()

code_dir = root_dir + "/" + "C_Code"

os.chdir(code_dir)

build_command = os.system("gcc -o section_5_3_dereferencing section_5_3_dereferencing.c")

exec_status = os.system("./section_5_3_dereferencing")

i is 20
i is 20