Write a function that concatenates two strings.Prototype: char *string_nconcat(char *s1, char *s2, unsigned int n);The returned pointer shall point to a newly allocated space in memory, which contains s1, followed by the first n bytes of s2, and null terminatedIf the function fails, it should return NULLIf n is greater or equal to the length of s2 then use the entire string s2if NULL is passed, treat it as an empty string

Here is a function in C that fulfills your requirements:

#include <stdlib.h>
#include <string.h>

char *string_nconcat(char *s1, char *s2, unsigned int n)
{
    char *concat_str;
    unsigned int len_s1 = 0, len_s2 = 0, i;

    if (s1 == NULL)
        s1 = "";
    if (s2 == NULL)
        s2 = "";

    while (s1[len_s1])
        len_s1++;
    while (s2[len_s2])
        len_s2++;

    if (n >= len_s2)
        n = len_s2;

    concat_str = malloc(sizeof(char) * (len_s1 + n + 1));
    if (concat_str == NULL)
        return NULL;

    for (i = 0; i < len_s1; i++)
        concat_str[i] = s1[i];
    for (i = 0; i < n; i++)
        concat_str[i + len_s1] = s2[i];
    concat_str[len_s1 + n] = '\0';

    return concat_str;
}

This function first checks if either of the input strings are NULL, and if so, treats them as empty strings. It then calculates the lengths of both strings. If n is greater than or equal to the length of s2, it sets n to be the length of s2.

It then allocates memory for the new string, which will be the size of s1 plus n plus 1 (for the null terminator). If memory allocation fails, it returns NULL.

The function then copies the characters from s1 and the first n characters from s2 into the new string. Finally, it adds a null terminator to the end of the new string and returns it.