strncat() function in C Language

strncat( ) function in C language concatenates ( appends ) portion of one string at the end of another string.
Syntax for strncat( ) function is given below.

char * strncat ( char * destination, const char * source, size_t num );

Example :

strncat ( str2, str1, 3 ); – First 3 characters of str1 is concatenated at the end of str2.
strncat ( str1, str2, 3 ); - First 3 characters of str2 is concatenated at the end of str1.

As you know, each string in C is ended up with null character (‘\0′).
In strncat( ) operation, null character of destination string is overwritten by source string’s first character and null character is added at the end of new destination string which is created after strncat( ) operation.

Example program for strncat( ) function in C Language:

In this program, first 5 characters of the string “fresh2refresh” is concatenated at the end of the string ”C tutorial” using strncat( ) function and result is displayed as “C tutorial fres”.

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#include <stdio.h>

#include <string.h>

int main( )

{

   char source[ ] = " fresh2refresh" ;

   char target[ ]= "C tutorial" ;

   printf ( "\nSource string = %s", source ) ;

   printf ( "\nTarget string = %s", target ) ;

   strncat ( target, source, 5 ) ;

   printf ( "\nTarget string after strncat( ) = %s", target ) ;

}

Output:

Source string = fresh2refresh
Target string = C tutorial
Target string after strcat( ) = C tutorial fres

Other String functions in C Language:

String.h header file supports all the string functions in C language. All the string functions are given below.

S.no	String functions	Description
1	strcat ( )	Concatenates str2 at the end of str1.
2	strncat.(.)	appends a portion of string to another
3	strcpy ( )	Copies str2 into str1
4	strncpy ( )	copies given number of characters of one string to another
5	strlen ( )	gives the length of str1.
6	strcmp ( )	Returns 0 if str1 is same as str2. Returns <0 if strl < str2. Returns >0 if str1 > str2.
7	strcmpi ( )	Same as strcmp() function. But, this function negotiates case. “A” and “a” are treated as same.
8	strchr ( )	Returns pointer to first occurrence of char in str1.
9	strrchr ( )	last occurrence of given character in a string is found
10	strstr ( )	Returns pointer to first occurrence of str2 in str1.
11	strrstr ( )	Returns pointer to last occurrence of str2 in str1.
12	strdup ( )	duplicates the string
13	strlwr ( )	converts string to lowercase
14	strupr ( )	converts string to uppercase
15	strrev ( )	reverses the given string
16	strset ( )	sets all character in a string to given character
17	strnset ( )	It sets the portion of characters in a string to given character
18	strtok ( )	tokenizing given string using delimiter

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