strncat in C language

The C strncat function is one of the String Function, which is used to append n number of characters from user specified string to end of the existing string.

In this article we will show you, How to use strncat in C Programming language with example.

C strncat syntax

The basic syntax of the strncat in C Programming language is as shown below.

char *strncat(char *destination, char *source, size_t n);

or we can simply write it as:

strncat(str1, str2, string_size);

• source: A valid string that you want to append to the destination
• destination: This is where the function will appeand the charcaters from Source.
• n: The number of character that you want to append from Source.

TIP: You have to include the #include<string.h> header before using this strncat string function.

strncat in C language Example

The strncat function is used to append the user specified string to existing string. This program will help you to understand the strncat with multiple examples.

/* strncat in C Programming to concatenate strings */
 
#include <stdio.h> 
#include<string.h>

int main()
{
   	char str1[] = "Learn";
   	char str2[] = "Learn";
   
   	char str3[] = " C Programming Language";
   	char str4[] = " at tutorialgateway.org";
	
   	strncat(str1, str3, 40);		
   	printf("\n The Final String after the Concatenation = %s", str1);
   
   	strncat(str2, str3, 10);
   	printf("\n The Final String after the Concatenation = %s", str2);
 	
   	strncat(str3, str4, 19);
   	printf("\n The Final String after the Concatenation = %s", str3);
   	
	getch();
	return 0;
}

OUTPUT

ANALYSIS

This statement will appeand all the characters in str3 to str1 because, length of C Programming Language is less than the given size 40.

strncat(str1, str3, 40);

This C strncat function will append first 10 characters present in str3 to str1 because, we are restricting the size to 10.

strncat(str2, str3, 10);

strncat in C Example 2

This program allows the user to enter source and destination strings. Next, it is going to concat them using strncat function.

/* string strncat in C programming Example */
 
#include <stdio.h> 
#include<string.h>
 
int main()
{
	char str1[100], str2[100];
 
	printf("\n Please Enter First String  : ");
	gets(str1);	
	
	printf("\n Please Enter the String that you want to concat : ");
	gets(str2);	
	
	strncat(str1, str2, 8);
	
 	printf("\n The Final String after the Concatenation = %s", str1);
	
}

OUTPUT

Although, the given string is a valid one, C strncat function only appended up to Tutorial. This is because, we restricted the concatination function to first 8 characters.

Let me change the Size value, and see

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