Concatenates a string of a specified length after another string.
char *strncat (char *s1, const char *s2, size_t n);
s1 Pointer to the string after which another string is appended
s2 Pointer to the string to be appended after the other string
n Number of characters to concatenate
The strncat function concatenates up to n characters from the beginning of the string specified by s2 at the end of another string specified by s1. The null character at the end of the s1 string is replaced by the first character of the s2 string. A null character is appended to the end of the concatenated string.