The snprintf function is identical to the sprintf function with
    the addition of the n argument, which specifies the size of the
    buffer referred to by str.

    On successful completion, snprintf returns the number of bytes
    (excluding the terminating null byte) that would be written to
    str if n is sufficiently large.

    If n is 0, nothing is written, the number of bytes (excluding the
    terminating null) that would be written if n were sufficiently
    large are returned, and str might be a NULL pointer. Otherwise,
    output bytes beyond the n - 1st are discarded instead of being
    written to the array, and a null byte is written at the end of
    the bytes actually written into the array.

    If an output error is encountered, a negative value is returned.