Appends not more than maxchar characters from str_2 to the end of
    str_1.

    Format

      #include  <string.h>

      char *strncat  (char *str_1, const char *str_2, size_t
                     maxchar);

1 - Function Variants

    The strncat function has variants named _strncat32 and _strncat64
    for use with 32-bit and 64-bit pointer sizes, respectively.

2 - Arguments

 str_1, str_2

    Pointers to null-terminated character strings.

 maxchar

    The number of characters to concatenate from str_2, unless
    strncat first encounters a null terminator in str_2. If maxchar
    is 0, no characters are copied from str_2.

3 - Description

    A null character is always appended to the result of the strncat
    function. If strncat reaches the specified maximum, it sets the
    next byte in str_1 to the null character.

4 - Return Value

    x                  The address of the first argument, str_1,
                       which is assumed to be large enough to hold
                       the concatenated result.