Null character in C

Introduction

The Null character in the C programming language is used to terminate the character strings. In other words, the Null character is used to represent the end of the string or end of an array or other concepts in C. The end of the character string or the NULL byte is represented by ‘0’ or ‘\0’ or simply NULL. The NULL character doesn’t have any designated symbol associated with it and also it is not required consequently. That’s the major reason it is used as a string terminator.

Note: The memory space for each character stored by NULL is 1 byte.

Null Character in C

Not only strings or arrays, there are various concepts in the C programming language which are terminated by a NULL byte. In concepts like Arrays, string literals, character strings a NULL byte is used to indicate the end of the string. This can be well illustrated using an example of an array.

Example: 

Suppose there is an array of size 10 and we need to store a string “computer” inside it. This can be simply done using the following piece of code;

char a[10] = "computer";

When this piece of code is executed, an array of size 10 is created with string “computer” inside it which looks something like this;

Here, the ‘\0’ is used to indicate the end of a string.

Note: The NULL character must not be overwritten with something else because it may lead to a condition where the end of the string cannot be determined.

Example:

In the above array, the a[8] represents the NULL byte and if it is overwritten, suppose

a[8] = “$” ; 

The array will now look like;

This is an issue because if we overwrite the ‘\0’ to ‘$”, there is no way to tell the end of the string.

Code correction:

In the above code, we are assigning the size of the array beforehand which may lead to problems sometimes, the good practice is to declare the array in the following manner;

char a[ ] = “computer”;

Here, the size of the string can be used to determine the size of the array since it happens at compile time, hence it is statistically typed and not dynamically typed. Now, the array will look like this;

Null Character in C vs Null pointer in C

Program: Print the value of ‘0’ and ‘\0’

#include<stdio.h>
 #include <string.h>  //header files
 int main()
 {


 printf ("The value of \\0 is %d \n", '\0');  // prints the value of \0
 printf("and the value of 0 is %d \n", '0'); // prints the value of 0
 return 0;


 } 

Output of the program:

The value of \0 is 0

and the value of 0 is 48

Advantages of using the Null Character in C

• By using the NULL character or NULL byte, we can quickly check whether a value is null or not.

• Generally, in C, we can use any other type of variable instead of NULL, but using such might require an explicit or external comparison for a specific value.

Every time we come across a comparison where the result of the comparison is ‘0’ or zero, then there is a change in the status register. A flag is automatically set in the status register. This can be used in conditional instructions (used for comparisons), such as conditional jump.

• Also, another advantage of using NULL is that it represents invalid value pointers.