strncpy() In C

Puropose Of strncpy()

strncpy() is one of the inbuilt string function in c programming which is used to replace a string with another string of required length.

How strncpy() Works

The following diagram clearly illustrate the working principle of strncpy() inbuilt string function in C.

In the above diagram strncpy() takes three parameters say str1, str2 and n. Here str1 and str2 are strings whereas n is of integer datatype. strncpy() simply replaces n characters of str1 with n characters of str2.

strncpy() Syntax

• strncpy() accepts three parameters.
• str1 and str2 is a strings which is of character datatype.
• n is a number which is of integer datatype.
• Here n describes, how many characters of str1 should be replaced with str2.
• To use strncpy() inbuilt string functions in C, we need to declare #include<string.h> header file.

strncpy(str1, str2, n);

C Program - strncpy()

Let us work through strncpy() function, In the following program we will replace n characters of str1 with n characters of str2 by using strncpy() inbuilt string function.

#include <stdio.h>
#include<string.h>
int main()
{
char str1[20] = "awesome strncpy", str2[10] = "This is ";
strncpy(str1, str2, 8);
printf("Str1 : %s ", str1);
return 0;
}

Str1 : This is strncpy

C Program - Without strncpy()

Let us replace n characters of str1 with n characters of str2 without using any inbuilt string functions.

#include <stdio.h>
#include<string.h>
int main()
{
char str1[30] = "awesome strncpy";
char str2[30] = "This is ";
int i, j, k, n = 8;
for(i=0; str1[i]!='\0';i++){
//making using of variable i
}
for(j=0; j<8; j++)
{
str1[j] = str2[j];
}
for(k=j; k!=i; k++)
{
str1[k]=str1[k];
}
printf("Str1 : %s ", str1);
return 0;
}

Original String : This is strcpy
Copied String : This is strcpy

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