String Functions in C

Introduction to C String Functions

We're often required to modify the strings and perform several operations on them according to our needs. If we want to get the length of the string, we could run a loop and calculate its length, but it is not the best way in case of complex problems. Hence, string functions are used to make our code efficient and straightforward as they are pre-written so we can use them directly.

The string handling functions are defined in the header file string.h. This header file must be included in the C program to use the string handling functions.

String Declaration

There are two ways to declare strings in C:

1. The following example will create a string as "Scaler" where the last character must always be a null character. The size mentioned within the brackets is the maximum number of characters a string could hold, and it is mandatory to give the size of a string if we are not initializing it at the time of declaration.

2. In this method, we do not need to put the null character at the end of the string constant. The compiler automatically inserts the null character at the end of the string.

String Functions

The following are the string functions in C:

Examples of String Functions in C

Let's look at an example to understand how string functions work in C.

strlen()

Syntax

size_t represents long unsigned int.

It takes a string (character array or character pointer) as input and writes the length of that string without including the end character '\0'.

Program Code

Output

strnlen()

Syntax

size_t represents long unsigned int.

strnlen() take a string and a positive integer maxlen as input and return the length of the string if maxlen is greater than the size of the string otherwise, always return maxlen which means it only counts the characters till str[maxlen -1].

Program Code

Output

strcmp()

Syntax

strcmp() takes two strings as input, then compares them, and returns an integer based on the following condition:

Program Code

Output

strncmp()

Syntax

size_t is for long unsigned int.

It compares only the first n characters of both the strings and returns an integer value accordingly:

Output

strcat()

Syntax

It takes two strings as input and concatenates the second string to the first string, which means it will attach the second string to the end of the first string and save the concatenated string to the first string. The size of the first string should be large enough to save the result.

Program Code

Output

strncat()

Syntax

It takes two strings as input and attaches only the first n characters of the second string to the end of the first string.

Program Code

Output

strcpy()

Syntax

It takes two strings as input and overwrites the data of the second string into the first string, i.e., it copies the data of the second string to the first string.

Program Code

Output

strncpy()

Syntax

size_t is long unsigned int and n is an integer.

It takes two strings as input and overwrites the data of the first string by the second string based on specific conditions:

If the length of string2 is greater than n, it copies only the first n characters of string2 to string1; otherwise, it copies the entire string2 to string1.

Program Code

Output

strchr()

Syntax

It takes a string and a character as input and finds out the first occurrence of the given character in that string. It will return the pointer to the first occurrence of that character; if found otherwise, return Null.

Program Code 1

• When the character is present in the given string

Output

Program code 2

• When the character is not present in the given string Notice the character 'z' is not present in the provided string. In such a case, it returns a null value.

Output

strrchr()

Syntax

It takes a string and a character as input and finds out the last occurrence of a given character in that string. It will return the pointer to the last occurrence of that character if found otherwise, return Null.

Program Code 1

Output

Program Code 2

• When the character is not present in the given string Notice the character 'z' is not present in the provided string. In such a case, it returns a null value.

Output

strstr()

Syntax

It takes two strings as input and finds out the first occurrence of the second string in the first string. It will return a pointer that points to the start of the first occurrence of the second string in the first string and a Null if the second string is not present in the first string.

Program Code

Output

strcasecmp()

Syntax

It takes two strings as input and compares them irrespective of their case sensitivity.

Program Code

Output

strncasecmp()

Syntax

It takes two strings as input and compares them till n characters irrespective of their case sensitivity. Program Code

Output