C - Array of Pointers

In this tutorial we will learn about array of pointers in C programming language.

We have so for learned about pointers and one dimensional arrays and pointers and two dimensional arrays. Feel free to checkout those tutorial.

Creating variables

For this tutorial we will create four integer variables.

// integer variables
int num = 10;
int score = 12;
int run = 123;
int goal = 3;

We can represent this in memory as follows.

We are assuming that an integer value takes 2 bytes so, each variable is taking 2 bytes space in memory.

Those memory spaces are filled with integer value which is not shown in the picture above.

Array of pointers

Since we have four integer pointers so, we can either create four separate integer pointer variables like ptr1, ptr2, ptr3 and ptr4.

Or, we can create one single integer array of pointers ptr variable that will point at the four variables.

In the following example we are creating an array of integer pointers ptr of size 4.

// array of integer pointers
int *ptr[4];

Assign address to array of pointers

This step is similar to any other pointer variable. We get the address of a variable using the address of & operator and then save that address in the array of pointers.

In the following example we are saving the address of the integer variables num, score, run and goal in the integer array of pointers variable ptr.

// assign address of variables to ptr
ptr[0] = #
ptr[1] = &score;
ptr[2] = &run;
ptr[3] = &goal;

Assuming that an integer address value takes 2 bytes so, each pointer element size is 2 bytes. So, the array of integer pointer ptr takes memory space from 8000 to 8007 i.e., total 8 bytes (2 bytes for each element).

The first element of the array of integer pointer ptr holds the address of the num variable.

Similarly, the second element of the array of integer pointer ptr holds the address of the score variable.

The third element of ptr holds the address of the run variable and the fourth element of ptr holds the address of the goal variable.

Access value of the variables via array of pointers

To access the value of the variables via array of pointers we have to use the value at the address of * operator.

// print value
printf("num: %d\n", *ptr[0]);
printf("score: %d\n", *ptr[1]);
printf("run: %d\n", *ptr[2]);
printf("goal: %d\n", *ptr[3]);

Complete code

#include <stdio.h>

int main(void) {
    
  // integer variables
  int num = 10;
  int score = 12;
  int run = 123;
  int goal = 3;
  
  // array of integer pointers
  int *ptr[4];
  
  // assign address of variables to ptr
  ptr[0] = #
  ptr[1] = &score;
  ptr[2] = &run;
  ptr[3] = &goal;
  
  // print value
  printf("num: %d\n", *ptr[0]);
  printf("score: %d\n", *ptr[1]);
  printf("run: %d\n", *ptr[2]);
  printf("goal: %d\n", *ptr[3]);
  
  return 0;
}

Output:

num: 10
score: 12
run: 123
goal: 3