Review of Pointer in C

In this short article we will review pointers in C programming language, if you are new to this kind of topic please read the tutorial of pointers for beginners first, try this tutorial for example.

Defining Pointer

There are several ways to define a pointer in C.

int* p;
int x = 5;

p = &x; // p pointer to address x

we can assign the address right away like so

int x = 5;
int* p = &x;

Dereferencing Pointer

Use * to dereference a pointer, this will return the value that the address of pointer is pointing at holds.

int x = 7;
int* p = &x;

int y = *p + 5; // 7 + 5 = 12

Updating the Address of Pointer

Assign the pointer to different address to make it points to different address.

int x = 5;
int y = 7;
int* p = &x;

printf("%d\n", *p); // 5

p = &y;

printf("%d\n", *p); // 7

Updating the Value of the Address the Pointer Pointed at

Use the dereference operator to update the value of address that pointer is pointing at.

int x = 5;
int* p = &x;

printf("%d\n", *p); // 5
printf("%d\n", x); // 5

*p = 8;

printf("%d\n", *p); // 8
printf("%d\n", x); // 8

Double Pointer

Use pointer to modify the value that the pointer is pointing at, use double pointer to modify the address that the pointer is pointing at.

Double pointer is commonly used as function parameters and two dimensional array.

char** s = (char**) malloc(2 * sizeof(char*));
s[0] = "hello";
s[1] = "there";
printf("%s\n", s[0]);
printf("%s\n", s[1]);

Afterword

Pointer in C programming language is one of the most feared aspect from its feature, however it is also the easiest way to learn about memory management.

Anyway, I’ll see you on another one.

Stay safe!