strncpy in C language

The C strncpy function is a String Function, which is used to copy n number of characters from one string to another. The syntax of the C strncpy function is

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

Or we can simply write the arguments as (str1, str2, size);

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

strncpy in C Example

This function is used to copy the user-specified string. This program will help you to understand the C strncpy method with multiple examples.

TIP: You must include the #include<string.h> header before using this strncpy Function.

The first statement will copy all the characters in str3 to str1 because the length of C Programming Language is less than the given size of 40.

The second statement will copy the first 9 characters present in str3 to str1 because we are restricting the size to 9.

#include <stdio.h> 

int main()
   	char str1[50], str2[50], str4[50];
   	char str3[] = "C Programming Language ";
   	strncpy(str1, str3, 40);		
   	printf("\n The Final = %s", str1);
   	strncpy(str2, str3, 9);
   	printf("\n The Final  = %s", str2);
 	memset(str4, '\0', sizeof(str4));
   	strncpy(str4, "Tutorial Gateway", 16);
   	printf("\n The Final = %s", str4);
 The Final = C Programming Language 
 The Final = C Program
 The Final = Tutorial Gateway

strncpy in C Programming language Example 2

This program allows the user to enter his/her own character array. Next, it will use the strncpy function to copy the user-specified string.

#include <stdio.h> 
int main()
	char str1[100], str2[100];
	printf("\n Please Enter the String that you want to Copy : ");
	//memset(str1, '\0', sizeof(str1));
	strncpy(str1, str2, 7);
 	printf("\n The Final String after Copying = %s", str1);

Although the given string is valid, this function is only copied. This is because we restricted the copy function to the first 7 characters (including spaces).

 Please Enter the String that you want to Copy : Learn C Programming

 The Final String after Copying = Learn C

Let me change the Size value and see

strncpy in C Language 3

About Suresh

Suresh is the founder of TutorialGateway and a freelance software developer. He specialized in Designing and Developing Windows and Web applications. The experience he gained in Programming and BI integration, and reporting tools translates into this blog. You can find him on Facebook or Twitter.